Have questions about C4 Corvette suspensions for your Tri5? Ask them here!

[chevynut]

I have been doing C4 conversions on Tri5 cars for over 10 years now. I am a mechanical engineer by profession, and have gained a lot of experience with both early ('84-87) and late ('88-96) C4 Corvette suspensions. My own '56 Nomad has the first conversion I designed and built.

If you have any questions about these awesome suspension conversions, what they entail, how they benefit you, any issues involved, or to help you make a choice between the early or late suspensions, or Dana 44 or 36 rears, please post them here. I'll answer them the best I can.

[Tabasco]

Yesterday there was a guy on Chevytalk that was asking about how to put a c4 Corvette rear end in a trifive wagon. Someone suggested he send you a PM. I replied that I wasn't sure you were still a member of the site, and I gave him your e-mail address. His screen name was c-towndave. Maybe he will contact you if he is serious.

[chevynut]

Hi Tobasco, thanks for the note and the referral. I appreciate it. Haven't heard from him yet ;) I do sell kits to install rearends, and have several rearends for sale.

[WagonCrazy]

Check the CT tri 5 customs forum Laszlo. There's a guy asking about where to get a 55 frame built. Several of us have referred him to you now. You might go on there and PM him...

[chevynut]

Paul, Tony won't let me on the site anymore. After I posted a link to Trifivechevys.com in a post about my Nomad update a year or more ago, he sent me a PM with the heading "GO TO HELL!" and banned me from the site. So f* him. I hardly ever visit the site anymore.

I appreciate you guys sending him my way. You could always tell him I'm over here and send him to this site, or to my classicedgedesigns.com website where he can send me an e-mail...or just give him my e-mail address. ;)

Thanks a bunch!

[chevynut]

I found the post...in the Nomad forum. I was alerted to it a couple of days ago by another member here. I really gotta get my website updated with more information. Got a lot of guys asking about frames.

BTW Paul we are on #41 now. ;)

[neill.jerry]

chevynut I talked to you about a boost bracket the other day . Thanks for all the help and info. Do you ever need corvette susp. parts I seen some on austin craigslist?

[chevynut]

Hi neill.jerry, I have several suspensions in stock, but I'm always looking for a deal. Turns out you got my LAST smooth bracket. Thanks!

[neill.jerry]

Thanks on the bracket. The corvette stuff is 1993 front and rear dana 36 and looks complete. Also what different hydo-boost fit your bracket.

[chevynut]

I'm pretty sure all the hydroboosters have the same mounting feature on the back. It's a threaded body and a big nut. The bracket is keyed to mount it with the accumulator away from the engine.

[hddm]

Hi, I have a 57 truck and I already have the 84 corvette. I want to do front and back suspention. What all do I need to install this in my truck? Thanks mike

[chevynut]

Mike, I don't offer a kit to modify truck frames for a C4 suspension. You might check with Flatout Engineering or Progressive Automotive, as I think at least one of them has a kit to do the job.

If you want to do it yourself, set the frame where you want it off the ground, set the suspensions up at the proper ride height, and figure out how to mate the two together. Good luck.

[Custer55]

I'm working on a C4 conversion on my 55 2 door sedan. I am close to the point of building the motor mounts and trying to figure out engine position. It looks like the engine will have to moved back from stock with firewall mods needed, or moved up and slightly forward for the balancer an pulleys to clear the C4 steering rack. This is for a small block chevy. I have a 4 speed with the stock bellhousing . Does this sound right, or am I missing something.
Thanks,

[chevynut]

We usually put a SBC 3/4" forward from stock. The damper has to sit over the top of the steering rack to avoid firewall modification. That's pretty much the case with any engine.

So the questions is, are you wanting a stock unmodified firewall or are you willing to modify it? If you try to use the stock C4 mounts, your engine will be back several inches into the firewall and offset to the passenger side. We cut them off.

Got any pics?

[Custer55]

That's what I figured based on the measurements. I guess I'll wait till I have the body back on the frame to decide what way to go. I'd rather have the engine back and lower down for better weight distribution and center of gravity, but lots more work to recess the fire wall, which affects a bunch of stuff under the dash too. Attached a few pics. The last one is what I want final ride height to be.
Thanks, for the input, Your frames look great.4065406640674068

[oceangoer]

Chevynut.

I sent you a PM earlier today , prior to finding this post.

I'm in need of C4 front IRS dimensions..

Michael..

[oceangoer]

Chevnut,

Thanks for the feedback.

I've decided to have the frame rails bent at AME, their located in Fife Wa, not that much of a drive from my place to pickup the rails and some other parts. And I favor a one piece frame rails. I'm just not wanting to fabricate complete frame rails yet again, and the price quote was significant less than I had expected.. We'll complete the frame rails drawings on Solid works. This is s soon as I finalize on the rear upper control arm angle, based on the IC etc.

Have you deviated from the "10 deg OEM" rear upper control arm angle in your builds ?

I decided rather than purchase a Dana 44 diffy and Bat wing plus the expensive rebuild to go with Dutchman's Aluminum 9 inch inch IRS. In the end the $$ spend is nearly the same and the 9 inch is significantly stronger and many more options. Mounting is a little easier and Dutchman's offer a cross member for the diffy case, which certainly make my life easier.

We will be fabricating the front suspension new cross member two inches narrower then (1988 and up) C4 OEM width. We've got the Rack selected and this member will mate to the new fame rails. appreciate your feed back !!

But, This project will be put on hold for about a month. I'm going in for my first knee replacement at the local V.A. Hospital next week, and I'm so very anxious to get this done. I'm sure to be stir crazy for a few weeks. But it's a one day event and I'll be walking in a few hours after the surgery.

I'll send you photos as we progress re the C4 suspension. Thanks again.

Michael....

[chevynut]

Have you deviated from the "10 deg OEM" rear upper control arm angle in your builds ?

Sorry, I don't understand your question. What rear upper control arm are you talking about? I use the stock C4 suspension geometry front and rear with the exception of the dropped rear toe adjuster which relocates the pivot points lower. I'm not sure how that affects the toe change, but Newman has used it on hundreds of builds, as have others, so it doesn't concern me.


I decided rather than purchase a Dana 44 diffy and Bat wing plus the expensive rebuild to go with Dutchman's Aluminum 9 inch inch IRS. In the end the $$ spend is nearly the same and the 9 inch is significantly stronger and many more options.

I rebuilt my Dana 44 and it wasn't that expensive even with the new 4.10 Viper (Dana) gears. I may have had $600 or so in it including the new gears (bought on eBay) and paying the local shop to set the ring and pinion up for me. They can be had for $1000 or so for the differential/batwing alone, and the Dutchman costs $1250 for just the housing...then you have to get the carrier, gears, mounts, and all the other parts needed. I'm betting you're into it for $3000 when it's all said and done. Then you'll need custom halfshafts, strut rods, etc. How do you plan to deal with the toe adjuster? Lots of custom fab work to implement that. Why not go with the Newman Dana 44 case or one from Street Shop? As far as strength, I have read that the Dana Super 44 or Dana 44 HD as it's often called is as strong as a 12 bolt GM rearend. And it's reported that the 12 bolt is as strong as a 9" Ford rear but I don't know for sure. Do you know the torque rating on a 9" differential?


We will be fabricating the front suspension new cross member two inches narrower then (1988 and up) C4 OEM width.

You should be at about 60" with a 2" narrower wheel mounting surface. Curious why you didn't go to 59" which is closer to stock tri5 width after going thru all that work. Have you checked into the kits that Flat Out Engineering offers for trucks? Maybe one of those would work and save you some fab time.

[WagonCrazy]

Have you checked into the kits that Flat Out Engineering offers for trucks?

I don't know if he did, but I just did and for about $3K I can get their front and rear C4 kit for my 59 Apache. All I have to come up with is the usual C4 bolt on parts. I'm now getting the idea that the truck needs to get Corvette suspension to go along with my Nomad's corvette setup. :cool:

[NickP]

sweet

[oceangoer]

Sorry, I don't understand your question. What rear upper control arm are you talking about? I use the stock C4 suspension geometry front and rear with the exception of the dropped rear toe adjuster which relocates the pivot points lower. I'm not sure how that affects the toe change, but Newman has used it on hundreds of builds, as have others, so it doesn't concern me.

I'm referring to the rear upper control arm (not the lower) "Dog Bone" that sits at 10 degrees relative to horizontal plane. The recommendations that I get are to lower to 8 degrees.

I'll be flipping the toe rods upside down a well, and cutting the spring perches of the rear spindles.

How are you handling the Ackerman with the longer WB, and does it remain a Positive ??



I rebuilt my Dana 44 and it wasn't that expensive even with the new 4.10 Viper (Dana) gears. I may have had $600 or so in it including the new gears (bought on eBay) and paying the local shop to set the ring and pinion up for me. They can be had for $1000 or so for the differential/batwing alone, and the Dutchman costs $1250 for just the housing...then you have to get the carrier, gears, mounts, and all the other parts needed. I'm betting you're into it for $3000 when it's all said and done. Then you'll need custom halfshafts, strut rods, etc. How do you plan to deal with the toe adjuster? Lots of custom fab work to implement that. Why not go with the Newman Dana 44 case or one from Street Shop? As far as strength, I have read that the Dana Super 44 or Dana 44 HD as it's often called is as strong as a 12 bolt GM rearend. And it's reported that the 12 bolt is as strong as a 9" Ford rear but I don't know for sure. Do you know the torque rating on a 9" differential?

I haven't found any Dana 44 complete for that low of a price. Narrowing the half shafts depends on wheel offset or typically each half shaft will require slightly over and inch cut, I don't have that number handle , My adjustable camber rods will remain original length, but a lower cradle wilt need to be fabricated. dana 44 with bat wing,,Locally their $1800.

I spoke with Newman a month or so ago, nice long conversation. He is retired and company is closed. He did tell me that he still had a few cases and other parts at that time ,. But he did not return my email and his web site seems to be shut down.



You should be at about 60" with a 2" narrower wheel mounting surface. Curious why you didn't go to 59" which is closer to stock tri5 width after going thru all that work. Have you checked into the kits that Flat Out Engineering offers for trucks? Maybe one of those would work and save you some fab time.

Yes, I know Don well, he's a great resource. I recently sent Don my excess collection of C4 suspensions parts that I don't need. I' getting quite a few small parts from Don. @ inch cut works for y wheel selection and the Mustang II rach is exactly 2 inches narrower and the pivot points.

[chevynut]

I'm referring to the rear upper control arm (not the lower) "Dog Bone" that sits at 10 degrees relative to horizontal plane. The recommendations that I get are to lower to 8 degrees.

I set the upper dogbone at about level at ride height, which is about as high as I can go the way I do it. If you try to put it any higher in front it's above the frame. I looked at what others have done there and Newman's was about the same as mine as far as I can tell. I don't know where guys are getting 8-10 degrees or how they're doing it.


I'll be flipping the toe rods upside down a well, and cutting the spring perches of the rear spindles.

Have you figured out how to handle the taper in the knuckles? I'm leaving the spring mounts on just in case for whatever reason I end up wanting to go back to a stock spring.


How are you handling the Ackerman with the longer WB, and does it remain a Positive ??

I'm not worrying about it. There are hundreds of C4 tri5s on the road and I've heard no complaints about Ackerman. Narrowing the front suspension makes it even worse.

The only way I know of to handle it is to shorten the wheelbase :eek: or change the steering arm angle. I know on their C5/6 front ends Morrison cuts off the steering arms and installs new ones. Part of that is to lower the rack, and I assume they also correct the Ackerman but not sure about that. I can't imagine they have different steering arms for every wheelbase.

Post some pics when you can.



Yes, I know Don well, he's a great resource. I recently sent Don my excess collection of C4 suspensions parts that I don't need. I' getting quite a few small parts from Don. @ inch cut works for y wheel selection and the Mustang II rach is exactly 2 inches narrower and the pivot points.

[55 Rescue Dog]

I'm still trying to wrap my head around the "Ackermann principal" There is a ton of info out on the subject. But generally I would think a short wheelbase needs much more Ackermann than something long like a bus. So, whether it's better or worse, moving a C4 suspension to a longer wheelbase, would tend to have more inner wheel steering angle than is needs? At least it will turn tighter corners that way in a parking lot. Or is it the other way around? Not that I would attemp to change it, just wondered what the effect might be on handling overall.

[oceangoer]

Chevynut,

I thought you know that This frame and suspension isn't going n my '56 210. I've decided to leave Her, Betty, alone and quit the every Winter "$$$ improvements" cycle that I've been doing for a decade. It's time to replace the headers , the plating is failing and headers are now available for the Rack & Pinion steering. But no hurry.

Rear control arms, " Dog Bones"

I typed that incorrectly. The OEM spec that I have is the "Lower Control Arm" is set at 10 degrees. Measuring my C4 Convert, there's a ~8 degrees difference, placing the upper a 2 degrees. But that's an estimate because both control arms are OEM and still have the rough casting parting edges making measuring them actually difficult.

You are correct in that the upper control arm will be close to level. Someday I might get deeper into this, but as long as I have resonable anti-squat I'll be happy. I'm still stumbling "Mentally" over the IC (instant center) at 34.7 horz and 17 vert, if that really needs to be lowered. Prob not.... The control arm mounting plate will be mounted on the frame Kick-Up and removable, I will be able to raise, lower or insert spacer plates if there's ever an issue. Simple enough to do this now than latter after.

Rear Spindle Toe in mounting hole Taper,

Yes, Don @ Flat Out has a great Toe Flip Kit and He includes tapers just for this issue. Take a look at the attached photo, I have more photos and can take a few more when my parts arrive, just let me know. I might be cramped for space, height, so We may drill the taper and insert a sleeve. I'll send you photos once I'm up and able to get back in my mini shop, Total Knee replacement next week at the V.A.. I hope to receive these components and front cross member next week. I still need to order the rear cross member from Dutchman's.


Ackerman

Yes, agree. I've seen so many custom and modified frames that if we all followed Ackerman, they wouldn't be close to derivable. I'm mostly concerned retaining Positive Ackerman resulting in positive toe-in when driving through a corner. We have some of the old Wheel Plates with a degree wheel, there crude but time will tell. I've heard and read about mod's on the C5/6 steering arms, but I don't recall seeing any on C4's. But, this isn't a endurance race car, I just need a safe and responsive driver.

Newman and others keep telling me Ackerman isn't an issue with C4's and longer a wheelbase. But you know since your also an Engineer, It's just something that I need to know.

I've been so busy finished my new home and small shop that I haven't watched your Nomad progress. Hope that going well! My '56 is a great driver, but she's just a stock body, I don't have the time nor patience to complete the workmanship and detail like yours.

I'll keep you up to date when we get started, photos too. Steve (lifelong friend a M.E. like you) is extremely detailed and will be doing the CAD design of my frame rails on our Solid Works. He's designed many a frame, and it's so nice to have him keeping me to such a high standard.

Thanks,

Michael..






6438

[chevynut]

Oceangoer, I'd be interested to see that toe adjuster flip kit...they don't show it on their site. Newman was still selling them but his site is completely shut down now. I need a source for them for my customers or else I'll have to put a kit together myself, which I really don't want to do. The picture you posted looks just like Newman's kit. When you get your toe flip kit could you send a pic of the kit contents to my email Lnobi53@yahoo.com?

This is the flip kit they show, and it looks like the bushing has no taper. I'm not sure what the other piece is for either.

http://www.flatout-engineering.com/assets/rear_toe_bar_flip_kit.gif

Looks like he's also figured out how to make new lines for the rack but the pics aren't very clear. I'm working on re-plumbing mine now and can't find anyone to make a good double flare at the cylinder end so I'm trying to figure out what to do. The valve end has a weird 0-ring flare that nobody can do either, so I'm using an AN adapter there.

Thanks!

[NickP]

Oceangoer, I'd be interested to see that toe adjuster flip kit...they don't show it on their site. Newman was still selling them but his site is completely shut down now. I need a source for them for my customers or else I'll have to put a kit together myself, which I really don't want to do. The picture you posted looks just like Newman's kit. When you get your toe flip kit could you send a pic of the kit contents to my email Lnobi53@yahoo.com?

This is the flip kit they show, and it looks like the bushing has no taper. I'm not sure what the other piece is for either.

http://www.flatout-engineering.com/assets/rear_toe_bar_flip_kit.gif

Looks like he's also figured out how to make new lines for the rack but the pics aren't very clear. I'm working on re-plumbing mine now and can't find anyone to make a good double flare at the cylinder end so I'm trying to figure out what to do. The valve end has a weird 0-ring flare that nobody can do either, so I'm using an AN adapter there.

Thanks!

Laszlo, I thought I sent you all of the images and dimensions from Newman's stuff.

[chevynut]

Nick, you might have but I don't recall. What kind of file was it? I have seen several of Newman's rear steer kits and I have a few tapered bushings that Gene from CT made me years ago but they're for me. :)

I don't understand what that is in the FOE picture. It looks like a sleeve you'd put in the knuckle to invert the taper, not eliminate it. But if you don't move the rods down at the inboard end as well it screws things up, I think.

How did you do yours, or did you use Newman's too? Also, how did you deal with the rack lines?

[oceangoer]

Here's what I have now,

Michael...

64396440[ATTACH]64416442

[NickP]

Nick, you might have but I don't recall. What kind of file was it? I have seen several of Newman's rear steer kits and I have a few tapered bushings that Gene from CT made me years ago but they're for me. :)

I don't understand what that is in the FOE picture. It looks like a sleeve you'd put in the knuckle to invert the taper, not eliminate it. But if you don't move the rods down at the inboard end as well it screws things up, I think.

How did you do yours, or did you use Newman's too? Also, how did you deal with the rack lines?

pdf and jpg I imagine - will look on shop computer. R&P Lines were inside the space between back of balancer and block - very close fit. I don't quite follow that image either. The walls don't look tapered.

http://pic20.picturetrail.com/VOL1600/2283636/23877721/410659060.jpg http://pic20.picturetrail.com/VOL1600/2283636/23877721/410659071.jpg

[chevynut]

Thanks for the pics guys. Michael, your chassis looks great! Your rear toe bar setup looks almost identical to Newman's kit, even the design of the aluminum center mount, with the exception that it's machined instead of cast aluminum. Is that the kit FOE is selling? I don't see anything like that on their product page, just the pic I posted. Here's Newman's:

6443

Nick, yours looks awesome too! Did Calvin use a BBC in that chassis? My SBC and LS engine dampers sit right smack over the top of that fitting and line. I thought Newman rotated the rack cylinder but I got to looking at his stuff recently and I noticed that one of the fittings is on top and the other was somehow moved to the bottom. I wonder how he did that.:confused:

6444

BTW, I designed a rear toe bracket almost identical to yours and I don't remember seeing it before I designed it...great minds think alike, huh? http://www.trifivechevys.com/images/smilies/biggrin-new.png I got one prototype from my laser guy to test.

Did you build the rear steer assembly from scratch? Mine will have to be narrowed so I can't really buy a kit. I'll have to get or make some shorter rods.

[oceangoer]

Cheynut,

Thanks but that's Don's @ FOE Diffy setup down in Orange CA. He's behind on the website updates, I've already teased him too much about it.

Since we're on the rear suspension, there's a nagging item that's bugged me for many years, re the rear Toe-in assembly. And before I get into this, I did recently look over some other rear IRS toe in setups, and their definitely shorter rods

My question is

Why aren't the inner Toe-in Pivots in line with the inner camber Pivots ??


Guess I'll need to check the Toe-in change when the rear spindles are moved from min to max....

Michael...

[oceangoer]

chevynut,

Forgot,

re the rotated Vette Rack, Turn One has the hyd lines all made up and will install on rebuilds, I thing they sell them OTC

turnone-steering.com

Michael...

[chevynut]

My question is Why aren't the inner Toe-in Pivots in line with the inner camber Pivots ??

I can't answer that because I haven't studied the rear suspension that thoroughly. I'm sure it has to do with getting the right amount of toe change, or NO toe change with suspension travel. The halfshafts, camber rods, and toe rods all work together.

I do know that the camber arm brackets for the late suspensions are different than on the early suspensions. In '88 they moved the inner pivots down to change the suspension geometry (lowers the roll center and decreases negative camber gain), and the late brackets could be used on an early suspension to make that same change.

[NickP]

Nick, yours looks awesome too! Did Calvin use a BBC in that chassis? My SBC and LS engine dampers sit right smack over the top of that fitting and line. I thought Newman rotated the rack cylinder but I got to looking at his stuff recently and I noticed that one of the fittings is on top and the other was somehow moved to the bottom. I wonder how he did that.:confused:

BTW, I designed a rear toe bracket almost identical to yours and I don't remember seeing it before I designed it...great minds think alike, huh? :-D I got one prototype from my laser guy to test.

Did you build the rear steer assembly from scratch? Mine will have to be narrowed so I can't really buy a kit. I'll have to get or make some shorter rods.

I had a Newman unit that I found on Ebay some time back. I drew it all up and made a dozen bracket pieces. It uses 1" DOM tube TIG welded together. I still have his casting piece. Calvin's 57 Nomad uses the stock cradle and the unit pictured is in a 57 2 door HT. Both are LS.

[55 Rescue Dog]

Just observing the stock set-up where the toe rods are very near the same plane as the axels, it would seem as you move them lower towards the camber rods you would see a bigger toe change through travel. Even more pronounced if the rear is narrowed. Modifying the frame, or raising the rear ride height would make it a non-issue, unless toe change is a good thing.

[chevynut]

it would seem as you move them lower towards the camber rods you would see a bigger toe change through travel. Even more pronounced if the rear is narrowed.

Keep in mind that the outboard end is also lowered as the inboard end is lowered. I'm not sure if there's a difference in the amount the inboard and outboard ends are moved on Newman's chassis. I think you'd have to lay it all out on paper or in CAD to see exactly what it does. Newman built hundreds of them and I've never read about any toe issues with his or other designs. Why don't you explain what the toe does with the stock setup? I don't see how you can simply say that narrowing a rearend makes it more pronounced without doing the analysis. It may actually make the geometry "better". Street Shop narrows the C4 rears up to 6".


Modifying the frame, or raising the rear ride height would make it a non-issue, unless toe change is a good thing.

Making c-notches in the frame to clear the toe rods weakens a frame that's already weak in the rear behind the humps. I built one frame where we extended the hump to allow the use of the stock toe rods, but he has to cut the trunk out to accommodate the modification. Raising the ride height negates much of the benefit of the C4 conversion by raising the CG, gives the car too much rake imo, and most guys looking for a performance chassis want the rear of the car as low as they can get it with at least 2-3" drop. A dropped toe adjuster, if properly designed, addresses all the issues.

[chevynut]

Here's an early C4 rearend drawing. Notice that the toe rod is horizontal and virtually parallel with the halfshaft, and above the halfshaft centerline. If the toe rod is lowered below the knuckle arm and the lower bolts are used as the inner pivot as Newman's kit does, it still sits essentially parallel with the halfshaft but sits on virtually the same centerline instead of above it. The inboard and outboard pivots are essentially just lowered and the angle doesn't change.

Also notice that the halfshaft is almost level, just barely lower at the outboard end. The strut rod points down and is about the same length as the halfshaft. As the suspension is compressed, it gains negative camber and the knuckle pivots around the outer u-joint. I'm not sure what the toe does, but since the stock toe rod is attached above the knuckle arm and longer than the halfshaft, I would think it would cause a slight toe in as the suspension compresses.

With the toe rod lowered along the halfshaft centerline, it looks to me like there would be little or no toe change as the suspension is compressed. I don't see how shortening the halfshaft and toe rod affects any of that.

What narrowing of the rearend does is steepen the angle of the lower strut rod, thereby shortening the distance to the instant center of the halfshaft and the strut rod. To correct that, all one would have to do is lower the inboard pivot point of the strut rod slightly as was done with the 88 and later suspensions. A narrowed late suspension probably still has the instant center further out than an early suspension, but I'd have to lay it out to confirm it. I already had some custom inner strut rod brackets cut. ;)

http://mobile.corvettestory.com/images/corvette-images-mobile/1984-Corvette-rear-view-outline-2_a.jpg

[chevynut]

Here's an early C4 rear...note the inner strut rod brackets:

http://tech.corvettecentral.com/wp-content/uploads/2013/11/Suspension-Lead-Shot-1.jpg


And here's a late C4 rear...the inner strut rod pivot is noticeably lower:

https://i.ytimg.com/vi/SqmXtmTL-j8/maxresdefault.jpg

[rockytopper R.I.P 5-13-2017]

What size wheels and or tires and what wheel offset works with the C4 setup in a trifive?

[chevynut]

What size wheels and or tires and what wheel offset works with the C4 setup in a trifive?

Front or rear? Early or late C4?

[rockytopper R.I.P 5-13-2017]

Front or rear? Early or late C4?
either and both front and back.

[Custer55]

What size wheels and or tires and what wheel offset works with the C4 setup in a trifive?
I have been running the stock 90 Corvette wheels and tires on mine for a while now with no clearance issues at all. I have the late C4 set up. Fronts are 9.5 x 17 wheels with 56mm offset, Rears are 17 x 9.5 wheels with 56mm offset plus a 3/16" spacer which makes it a 51mm offset with the spacer. Tires all the way around are 275/40/17 (stock size for the 90 Vette) I think a 285 tire would be fine in back. In the front I will probably eventually go to a 255 tire just to lower the front of the car a bit. Not sure if this would work on any C4 conversion but it is working on mine.
Brian :cool:

[chevynut]

I have the late C4 set up. Fronts are 9.5 x 17 wheels with 56mm offset, Rears are 17 x 9.5 wheels with 56mm offset plus a 3/16" spacer which makes it a 51mm offset with the spacer. Tires all the way around are 275/40/17:

Custer per my calculations your front tires are 68.4" across and I'm surprised they don't rub. Most guys start having problems at around or a little over 68" but that's with stock suspension geometry and steering. The c4 setup turns differently and not as far. Yours is a 55 so you have more room too. Have you turned sharply with the suspension compressed like driving into a steep driveway? How much did you drop the front from stock?

Maybe 68" to 68.5" works fine with the c4 setup since yours seems to work. How close are you tires to the frame at full lock?

[chevynut]

What size wheels and or tires and what wheel offset works with the C4 setup in a trifive?

In the rear a 275 tire works without mini tubs with the limiter being the tubs at 46.5" wide. You actually have about 12.5" to work with in the wheel well. You might squeeze a 285 in there but it would be pretty tight. Once you minitub it the dog bones become the limiter and you can go 295 or possibly 305 depending on how tight you want the clearances. You can go really close to the dogbone. To go any bigger you'd have to narrow the rearend which you can't do much without narrowing the frame. I think you can get away on the big end with a 55 nomad with the big wheel openings.

[Custer55]

Custer per my calculations your front tires are 68.4" across and I'm surprised they don't rub. Most guys start having problems at around or a little over 68" but that's with stock suspension geometry and steering. The c4 setup turns differently and not as far. Yours is a 55 so you have more room too. Have you turned sharply with the suspension compressed like driving into a steep driveway? How much did you drop the front from stock?

Maybe 68" to 68.5" works fine with the c4 setup since yours seems to work. How close are you tires to the frame at full lock?


My suspension drop is about 3" The frame is 4" off the ground at the kick up at the firewall. I try not to go to fast in and out of drive ways and angle through them if there steep. At full lock there isn't much clearance to the tire at the fender or the frame, maybe 1/4" to 1/2", but like I said I have not had anything rubbing to this point. The C4 suspension design may be the reason it works as I had rubbing issues with the stock suspension with McGaughys 2" drop spindles at the top of the fender opening with 235 tires on the front on sharp turns at 15 to 20 mph.
Brian

[rockytopper R.I.P 5-13-2017]

OK thanks. Cluster pretty much answered my question. I ask this because every trifive C4 conversion I've found pictures of are running corvette wheels. The 2 inch back spacing required explains why. The C4 conversion pretty much forces a pro-touring look there aren't any old school wheels of any width that would work giving the front spacing is more or less 3.25 inches if cluster is close to the max envelope.

Rocky

[NickP]

Who's Cluster? LOL

[chevynut]

I ask this because every trifive C4 conversion I've found pictures of are running corvette wheels. The 2 inch back spacing required explains why.

All you really needed to see that is the suspension widths. The early ones are 61" front 62" rear. The late ones are 1" wider. And you don't have to use Corvette wheels. Any wheel with the right offset works. Wade's nomad pictured on my website has a late front end and Boyd's wheels.




The C4 conversion pretty much forces a pro-touring look there aren't any old school wheels of any width that would work

Why would anyone want "old school " wheels on a C4 conversion?😳 Again, ANY wheel with the right offset will work. An early C4 setup can handle about 1/2" less offset.

[rockytopper R.I.P 5-13-2017]

[QUOTE=chevynut;35155]All you really needed to see that is the suspension widths. The early ones are 61" front 62" rear. The late ones are 1" wider. And you don't have to use Corvette wheels. Any wheel with the right offset works. Wade's nomad pictured on my website has a late front end and Boyd's wheels.

I'm not implying 15 inch lol, I stand corrected the earlier version does give room to not have a flat faced wheel that's all I mean. The 57 on your site is a prime example.

[chevynut]

Wade's blue nomad has the wider late front end with an early rear. I think the wheels look great.

A lot of guys have the misconception that you have to use corvette wheels.

We built a frame earlier this year that's planned to use stock 15" steel wheels and white walls.

My nomad has a stock tri5 width (60") narrowed late C4 rear.

[NickP]

Nick, you might have but I don't recall. What kind of file was it? I have seen several of Newman's rear steer kits and I have a few tapered bushings that Gene from CT made me years ago but they're for me. :)


http://pic20.picturetrail.com/VOL1600/2283636/23877721/412867464.jpg

[55 Rescue Dog]

As touchy as IRS rear suspensions can be, I'm afraid to move anything from stock. Even GM has struggled since 1960 with it, but finally seems to have it sorted out, with no "jacking effect", that even the C4's can have when you mess with it. Surely the toe rod makes no difference on the geometry from what I've read. Still trying to get an idea as to what the changes in wheelbase, and mass between the C4, and the tri-five have? 2 totally different cars it seems in some ways. No free lunch.
Would love to hear how narrowing the C4 suspension would be a benefit for handling, to get a bigger tire under it? My un-informed thought is widening the rear track width would help. On my C5, and BMW M Roadster the rear is wider than the front for some reason.

[chevynut]

As touchy as IRS rear suspensions can be, I'm afraid to move anything from stock.

What's "touchy" about an IRS? The same suspension geometry principles apply to an IRS as they do to an IFS. Think about the rear toe adjuster the same as the front steering rods. When going forward, they just keep the tires centered. If the pivot points are wrong on the steering rods, you'll get bump steer. Same in the rear. If the rear toe rods are parallel to the halfshafts and the same length, they won't affect toe as the suspension moves. In reality, the toe rods are slightly longer than the halfshafts but they pivot at points further inboard on both ends. I think any toe change over the 2" or so of up/down suspension travel is minimal because the components are so long....longer than the front a-arms and rods.

As usual, you over-complicate things and think that GM got everything "perfect". If you don't understand what's changing, you probably shouldn't move anything unless it's proven. I think Newman and others have proven that the dropped toe adjuster works just fine. There are probably a couple thousand examples driving around.

I have no issue with moving the toe rods down so they clear the frame because I think any effect is minimal, and if I thought it was a problem I'd do more analysis. Of course, if you want to leave the rear of the car at around stock height you can leave them in the stock location.



Even GM has struggled since 1960 with it, but finally seems to have it sorted out, with no "jacking effect", that even the C4's can have when you mess with it.

The Corvette didn't have an IRS until 1963. GM didn't "struggle", they just kept improving it over the years. That's how designs evolve. The C3s used a solidtrailing arm setup with no toe adjuster in the rear of the differential. That caused suspension geometry issues and wasn't as "independent" as it could have been. Camber changes twisted the trailing arms. The C4 improved upon that by using dual trailing arms, improving anti-squat performance and camber gain and overall flexibility of the suspension. The C5/6/7 rear design is an improvement on the C4 with the unequal length a-arms like an IFS. That allows the rear to have a constant anti-squat since the a-arm angles don't change. It took a while for some reason, but GM finally got to where Porsche, Ferrari, and other exotics have been for a long time.

What do you mean "mess with it"? If you understand what's changing you can "mess with it". Lots of chassis manufacturers "mess with" the pivot points on an IFS and rack location. Maybe you shouldn't http://www.trifivechevys.com/images/smilies/tongue-new.png. C4 suspension components are commonly used with narrowed k-members and custom front crossmembers that are narrower than stock. What are you calling a "jacking effect"?


Surely the toe rod makes no difference on the geometry from what I've read.

It makes no difference on anything but toe in or out during suspension travel. A solid rear has no toe movement with suspension travel. Is that ideal, or should you have some toe in/out going into turns? Which way is "best"?


Still trying to get an idea as to what the changes in wheelbase, and mass between the C4, and the tri-five have? 2 totally different cars it seems in some ways. No free lunch.

The wheelbase goes from 96.2" for the C4 Corvette to 115" for the tri5. That's pretty significant change but it affects nothing that I know of but the Ackerman and steering radius. What's the "ideal" Ackerman? Again, there are a few thousand tri5 cars running around with C4 suspensions so the Ackerman is probably not a big issue. Nobody has complained about any negative Ackerman effects that I'm aware of. The weight of the cars is comparable...both around 3200-3400 pounds and a couple hundred more isn't going to change much imo. Both are just cars and behave similarly with the same suspension geometry. Does this keep you up at night? http://www.trifivechevys.com/images/smilies/biggrin-new.png


Would love to hear how narrowing the C4 suspension would be a benefit for handling, to get a bigger tire under it? My un-informed thought is widening the rear track width would help. On my C5, and BMW M Roadster the rear is wider than the front for some reason.

Most cars have a wider rear track width than the front, even a stock tri5 is a little wider in the rear than the front. And "track" doesn't refer to the wheel mounting surface width, it's the center of the tires when installed on the car. An 88-91 C4 Corvette has an actual rear track width of 60.4" and a front track width of 59.6", almost identical to a stock tri5 with zero offset wheels. A 92 and later is 59.1" rear and 57.7 front according to my C4 specs book.

Narrowing a C4 rear allows the use of a wider tire, because it moves the dogbones inboard. The outboard limiter is the quarter panel and the inboard limiter is the dogbones. You can't move the quarter panel, but you can move the dogbones if you narrow the frame. I can put 345 rear tires under my Nomad and keep them comfortably inside the quarter panels. It's also an aesthetic thing, since some guys like a deeper dish wheel, and it makes the wheels easier to remove. You don't need to narrow the rear to get a 295 or 305 tire under a tri5 with a C4 suspension, but any more than that and you have to. We've built 3 frames with narrowed rails for bigger rear tires but it takes a lot of work. My Nomad rear is the same width as a stock tri5 so I can use the the same wheel frontspacing if I want. I don't believe handling is negatively affected by narrowing the rear 1.5" per side since my roll center is lower than an early C4 and I could move it even lower with a simple inboard strut rod bracket re-design.

If you think something is detrimentally affected by narrowing the C4 IRS, what is it? Of course as usual you want to confuse and complicate everything more than it needs to be and question everything I have done. Besides, you have a stock width rear (at close to stock height) and it can't be narrowed without serious frame surgery, so why do you care?:confused:

[55 Rescue Dog]

Okay, so you can do whatever you want to an IRS I guess. I would love to see a narrowed one autocross, and prove it won't jack like a swing axel Corvair, unless it has a roll center underground. I would think a 345 tire's centerline would move it inboard a lot from a stock tri-five regardless of the outboard width. A straight axel might have zero toe change, but the roll steer can be a big factor in making the car turn.

[chevynut]

Okay, so you can do whatever you want to an IRS I guess.

Lots of guys narrow the C4 IRS as I said, and they also narrow the C4 IFS. According to you that's a no-no. Lots of guys use dropped toe adjusters but you seem to have some sort of concerns about it that you can't articulate or prove. Some guys use adjustable dogbones and I'm guessing you have some kind of an issue with that too. You have an issue with poly suspension bushings, with coilovers, and with just about everything GM didn't do but many others have.

Guys use different offset wheels on a C4 suspension, depending on the vehicle the suspension is going into. There's nothing "magic" about an IRS. Yes, you can do just about anything you want with it if you understand how it works. You probably shouldn't mess with yours.:eek:


I would love to see a narrowed one autocross, and prove it won't jack like a swing axel Corvair, unless it has a roll center underground.

Yours might "jack" since it's at almost stock tri5 height :p. If mine "jacks" so does yours. I don't think you know what causes what you call "jacking" and the C4 rear is nothing like a Corvair or VW rear suspension. Why would a narrowed rear cause "jacking" anyhow? Can you explain it? You apparently don't even understand what changes when you narrow the IRS and keep the track width the same. All you have to do is change the wheel offset to make things fit. Mine is narrowed 1.5" per side...hardly enough to make much difference in geometry. That's less than 10% of the length of the halfshafts. Why don't you calculate what that did to the roll center? And as I said, the roll center now falls somewhere between an early and late C4, and closer to the late one. Do you understand what moving those inboard strut rod brackets does?

I would love to see you have a debate and actually quote facts and figures, instead of your unfounded opinions and beliefs.


I would think a 345 tire's centerline would move it inboard a lot from a stock tri-five regardless of the outboard width.

Well you only have so much room outboard until you hit the quarter panel, so if you want a bigger tire you have to go inboard or put fender flares on the car. This stuff seems to confuse you a lot for some reason :D. If I put a 345 tire on my car with 1/2" clearance at the quarter panel lip, the track width would be about 57.25". The center of the stock wheelwell with relocated springs is 59.125". That's a difference in track width of 1 7/8". Each 345 tire centerline is 15/16" inboard of the center of the stock wheelwell. The center of a minitubbed wheelwell with springs relocated is about 57.125" which would make it slightly narrower than mine if a tire was centered in it. In fact, the stock tri5 rear track width is 58.9". The differences aren't that big, and if you tried doing a little math once in a while to try to prove this to yourself you wouldn't have to bring stuff like this up.:geek:

I can put a 345 tire on my car and the CG is lower than yours is. You max out at a 295 tire with a stock C4 rear IF you have minitubs, and about a 275 without them. Big tires and a low CG help on the skidpad and slalom..that's why exotics and super cars run such big tires. Sure, you could drop yours to lower the CG but then the suspension geometry will be all screwed up. The ride height needs to be built into the frame design.

You're better off leaving everything as GM made it, so you don't fret about it so much. But don't attack what others do to theirs unless you first try to understand what you're talking about. :D

[NickP]

As an aside to this, relative to width at the hubs, an email I have from Bob Shetrone, AKA Progressive Automotive states, "1988-96 can be narrowed to 58.5” hub width & 1984-87 can be narrowed to 57.5” hub width"


They have a slew of them out there and seem to be fully functional.

[chevynut]

Nick, I think that refers to the front suspension, but I know Progressive also narrows rear suspensions. Front suspensions have to be narrowed a specific amount to fit the narrower racks they use. You can narrow a late rear suspension to about 60" before you run into clearance issues between the batwing and the knuckle. I actually clearanced the knuckles on my suspension to give better clearance for the batwing, since I didn't narrow the batwing. If you narrow the IRS much more than 60" you have to narrow the batwing. Maybe that's where they get the 58.5/57.5" in the rear because that's pushing it.

[NickP]

I had inquired as to the cost of narrowing the rear batwing and the half shafts.

Nick,
Narrow Rear Cover with new urethane rear cover bushing installed
Narrow toe-in (tie bar) adjuster
Narrow Half shafts with new half shaft u-joints installed
Custom built camber bars
$1,650.00

1988-96 can be narrowed to 58.5” hub width
1984-87 can be narrowed to 57.5” hub width

Best Regards,
Bob Shetrone, Pres.
Progressive Automotive, Inc.
125 West Rome St.
Baltimore, OH. 43105
Phone: 740 862-4696
8:00 AM -4:00 PM, Monday-Friday ET
ProgressiveAutomotive.com
file:///C:/Users/Prime/AppData/Local/Temp/msohtmlclip1/01/clip_image001.jpg

[chevynut]

Interesting Nick. I wonder why it's limited to 58.5"/57.5" if they narrow the batwing too. Maybe it's the width of their frame rails or something like that. At 58.5" at the mounting surfaces (with discs) a late C4 suspension is narrowed almost 5" which is pretty significant. Tray Walden at The Street Shop told me he's narrowed them as much as 6" for early Corvettes. Do you think they're just "jacking" around? :D :p

[NickP]

Interesting Nick. Do you think they're just "jacking" around? :D :p

LOL. I understand the term and it's quite common with "SWING AXLE" vehicles - BTW, they might be an IRS version but yards different in reaction - that's the whole reason VW went to a true IRS.

[Rick_L]

Ditto what Nick said. The VW and early Corvair suspensions have a swing axle, which only has a u-joint at the inboard end of the axle. Camber changes with suspension movement. "Jacking" occurs when the car is driven hard.

Late VWs, Corvairs and C2/3/4 Corvettes have 2 u-joints on each axle. "Jacking" does not occur.

[55 Rescue Dog]

The C4 can still gain positive camber in droop, and that is bad, which can cause jacking. That was the swing axels problem. Positive camber gain on rebound. It just should be a consideration when making any changes to width, etc. Might never be an issue until you find out after you hit a dip in the road at max corner speed. My first car was a 1964 Corvair Spyder, and it handled great, not knowing, or wondering why back then. Drove the crap out of that car. 1964 was the one and only year they "fixed the car" with a traverse leaf spring! Still haven't figured out how that worked so well on that car.

[Rick_L]

64 Corvair still had the swing axle. 65-69 had the double u-joint axles. The 65-69 suspension was very similar to the C2/C3 Corvette setup except it had the transaxle and rear mount engine. Not sure what was fixed on a 64 if anything.

Nader wrote his book "Unsafe At Any Speed" about the early Corvair (60-64). It was an ill handling car. However the late Corvair (65 up) was a great handling car. I learned a bit about those cars when I was in college, as 3 graduate assistants had late Corvairs, two of them modified with a 4 bbl carb and extra boost on the turbo, the other was the N/A 4 carb option. That and GM had donated a bunch of Corvair parts to the school.

[55 Rescue Dog]

FRNADER, was the most favorite license plate I've seen. The YENKO Stinger Corvairs were SCCA national champs many times. Personally saw one blow everything away in Salina in 1984. Very fast. Charlie Clark out of New Jersey I believe.

[55 Rescue Dog]

Has anyone ever heard of a "Z bar" they used back in the day on the swing axel race cars? I don't remember at the moment, but weren't the 356 Porsche's swing axels?

[chevynut]

The C4 can still gain positive camber in droop, and that is bad, which can cause jacking. That was the swing axels problem. Positive camber gain on rebound. It just should be a consideration when making any changes to width, etc.

Changing the width of the C4 rearend doesn't change the geometry significantly. I already explained what happens when a C4 rearend is narrowed. The halfshafts are still essentially level, and the strut rods are at a slightly steeper angle toward the differential. It moves the instant center closer to the center of the car, which raises the rear roll center a tad. It does little to affect the camber curve within the range of normal suspension movement. And if one thought it was a problem he could adjust the inboard strut rod brackets to compensate. As I said, the early C4 strut rods already point up steeper than the late ones and they perform fine.

How much positive camber gain does a C4 rearend allegedly have in 2-3" of droop? The strut rods are longer than the halfshafts and you start at -1/2 degree so where does it end up? Come up with numbers and you'll be more credible.

Did you give up on your insistence that a wider tire and narrower track width somehow adversely affects handling? I wonder why so many fast autocross cars use tubs that allow the bigger tires to fit under the car, narrowing the track width. :D

[NickP]

How much positive camber gain does a C4 rearend allegedly have in 2-3" of droop? The strut rods are longer than the halfshafts and you start at -1/2 degree so where does it end up? Come up with numbers and you'll be more credible.

If I had some dimensions, I'd do a drawing and settle it.

[NickP]

Has anyone ever heard of a "Z bar" they used back in the day on the swing axel race cars? I don't remember at the moment, but weren't the 356 Porsche's swing axels? Yes, however, a C4 is not a swing axle IRS.

6462

[chevynut]

Yes, however, a C4 is not a swing axle IRS.

Yeah, so maybe we can stay on topic now. :)

[NickP]

Yeah, so maybe we can stay on topic now. :)

6463

[chevynut]

If I had some dimensions, I'd do a drawing and settle it.

Since RD doesn't ever seem to want to be bothered with measurements, numbers, and facts, I figured I might as well measure the C4 rear dimensions myself. :D

The stock halfshafts are 18.125" long and the lower strut rods are 18.375" long. The distance between the two inner u-joints is 14.75" and the distance between the two inner strut rod pivots is 13.188". That makes the strut rod pivot .781" inboard of the u-joint center. The vertical distance between the strut rod inner pivot and the center of the inner u-joint is 5" (this was a LATE suspension). The vertical distance between the strut rod outer pivot and the center of the outer u-joint is 6".

All dimensions for an early suspension are the same except for the vertical height of the strut rod inner pivot.

The distance between the inner toe adjuster rod pivots is 3" (as close as I can tell) and the rods are 21" long. The inboard pivots are vertically 6.5" above the inboard strut rod pivots. I'd just assume the rods are parallel to the halfshafts, which is close. I think you have the location of the dropped toe rod inner pivots.

My rear suspension is narrowed 1.5" per side, so halfshafts are 16.625" long.

That should give you enough info to lay it out and see how camber changes from a static -.5 degrees from -3 to +3" suspension travel. The toe rods don't do anything to camber but I put the measurements here for further analysis.

[NickP]

Since RD doesn't ever seem to want to be bothered with measurements, numbers, and facts, I figured I might as well measure the C4 rear dimensions myself. :D

The stock halfshafts are 18.125" long and the lower strut rods are 18.375" long. The distance between the two inner u-joints is 14.75" and the distance between the two inner strut rod pivots is 13.188". That makes the strut rod pivot .781" inboard of the u-joint center. The vertical distance between the strut rod inner pivot and the center of the inner u-joint is 5" (this was a LATE suspension). The vertical distance between the strut rod outer pivot and the center of the outer u-joint is 6".

All dimensions for an early suspension are the same except for the vertical height of the strut rod inner pivot.

The distance between the inner toe adjuster rod pivots is 3" (as close as I can tell) and the rods are 21" long. The inboard pivots are vertically 6.5" above the inboard strut rod pivots. I'd just assume the rods are parallel to the halfshafts, which is close. I think you have the location of the dropped toe rod inner pivots.

My rear suspension is narrowed 1.5" per side, so halfshafts are 16.625" long.

That should give you enough info to lay it out and see how camber changes from a static -.5 degrees from -3 to +3" suspension travel. The toe rods don't do anything to camber but I put the measurements here for further analysis.

For accuracy's sake, batwing eye to eye = ? Yoke to yoke on center section=14.75? hub to hub (including hat)? Upper and lower dogbone? Distance from rear knuckle centerline to center of dogbones? I used to have a file of all of the dims but lost most of it in HardDrive crash.

[NickP]

Also, distance from centerline of inner yokes to centerline of lower strut? The 13.188 dim, isn't that the adjustable unit? Distance of knuckle center to lower strut?

[55 Rescue Dog]

Of course I wish now I would have paid more attention in geometry class, and knew CAD, but just eyeballing the stock rear, the outer toe rod joint appears to be perfectly in line with the centerline of the outer u-joint so it should follow the arc of the half shaft which is like the upper ball joint. Wouldn't moving the outer toe pivot closer the lower link magnify toe changes since it moves in and out more than the centerline of the axel? And even more so if narrowed?

[chevynut]

I did a quick layout using the dimensions I posted above for a late C4 suspension and my lower strut rod angle only changes by 0.28 degrees (steeper) with a 3" narrowed late C4 rear. :) It's pointing up at 3.12 degrees with the stock suspension and halfshafts level, and up at 3.40 degrees with 1.5" shorter halfshafts. The angle change moves the IC from 85.1" on the opposite side of the chassis centerline to 77.6". That moves the roll center up by a whole 0.138". Should I be worried? :D

Going to the early C4 camber brackets moves the roll center up more since the inboard strut rod pivot is higher. Both suspensions work great and I'm not sure which performs better. Theoretically having a roll center closer to the CG decreases the roll moment arm length, which should decrease the tendency to roll.

Haven't looked at camber yet, but I'm sure the change with a narrowed rearend is just as insignificant.

[NickP]

here is what I see. Not much movement.http://pic20.picturetrail.com/VOL1600/2283636/5293467/412882040.jpg

[NickP]

http://pic20.picturetrail.com/VOL1600/2283636/5293467/412883326.jpg

[chevynut]

here is what I see. Not much movement.

Thanks Nick, that looks right. If I understand your numbers correctly, the upper pivot point moves inboard .062" while the lower one moves inboard .020" with 3" of compression. The lower one first moves outboard over the first 1" of compression, then moves inboard. That's a change of .042" over 6" which is a camber angle change of -.40 degrees at 3" compression.

The early suspension would actually give slightly more negative camber gain since the inner strut rod pivot is a little higher.

What numbers do you get if you shorten the halfshaft and strut rod by moving both outer pivots inboard 1.5" horizontally? Again, I think the change is minimal but I probably gained just a little more negative camber.

[NickP]

Thanks Nick, that looks right. If I understand your numbers correctly, the upper pivot point moves inboard .062" while the lower one moves inboard .020" with 3" of compression. The lower one first moves outboard over the first 1" of compression, then moves inboard. That's a change of .042" over 6" which is a camber angle change of -.40 degrees at 3" compression.

The early suspension would actually give slightly more negative camber gain since the inner strut rod pivot is a little higher.

What numbers do you get if you shorten the halfshaft and strut rod by moving both outer pivots inboard 1.5" horizontally? Again, I think the change is minimal but I probably gained just a little more negative camber.

http://pic20.picturetrail.com/VOL1600/2283636/5293467/412883857.jpg

[chevynut]

Thanks again Nick for the drawing for the narrowed suspension. However, I just noticed that you're showing a total travel of 3", 1.5" up and 1.5" down. I was looking for a total travel of 6", 3" up and 3" down in each case.

[NickP]

Thanks again Nick for the drawing for the narrowed suspension. However, I just noticed that you're showing a total travel of 3", 1.5" up and 1.5" down. I was looking for a total travel of 6", 3" up and 3" down in each case.

6"! Every woman's dream. Big pot holes? Not an issue............................................. ................................................

[chevynut]

For accuracy's sake, batwing eye to eye = ?

37 3/8"


Yoke to yoke on center section=14.75?

Yes. Actually u-joint center to u-joint center.


hub to hub (including hat)?

I get 63 1/4" measured for a late suspension, 62 1/4" measured for an early one.


Upper and lower dogbone?

Front spacing of dogbones is different early vs late. The late suspension is 4.156" and the early one is closer, but I don't have the measurement handy. I have several early and late brackets though.

[chevynut]

just eyeballing the stock rear, the outer toe rod joint appears to be perfectly in line with the centerline of the outer u-joint so it should follow the arc of the half shaft which is like the upper ball joint.

No, the outer toe rod pivot is 3" inboard of the outer u-joint centerline. Also, the toe rod is 21" which is longer than the halfshaft at 18.125". The toe rod swings in a larger arc than the halfshaft.


Wouldn't moving the outer toe pivot closer the lower link magnify toe changes since it moves in and out more than the centerline of the axel? And even more so if narrowed?

Again, the entire toe rod is dropped, not just the outboard or inboard end. So the arc traveled is the same. With a narrowed rear the arc would be smaller but it's only a 7% change in rod length. And since the travel is only 2-3" at the end, it's not significant. I could probably change the outboard spacer height to make it toe exactly like a stock rear on a given compression.

[NickP]

http://pic20.picturetrail.com/VOL1600/2283636/23877721/412884084.jpg
http://pic20.picturetrail.com/VOL1600/2283636/23877721/412884086.jpg

[NickP]

No, the outer toe rod pivot is 3" inboard of the outer u-joint centerline. Also, the toe rod is 21" which is longer than the halfshaft at 18.125". The toe rod swings in a larger arc than the halfshaft.



Again, the entire toe rod is dropped, not just the outboard or inboard end. So the arc traveled is the same. With a narrowed rear the arc would be smaller but it's only a 7% change in rod length. And since the travel is only 2-3" at the end, it's not significant. I could probably change the outboard spacer height to make it toe exactly like a stock rear on a given compression.

Where are the three triangle pattern bolt holes relative to axle centerline? I can add that too. Stock

[chevynut]

Thanks Nick, I went ahead and laid it out and got the same numbers you did. Here's the camber change calculations for 3" up and down with a late C4 suspension....

For the stock width case, the camber in compression (bump) changes -1.60 degrees and in extension (droop) it changes +1.56 degrees.

For the 3" narrowed case, the camber in compression (bump) changes -1.76 degrees and in extension (droop) it changes +1.70 degrees

So the narrowed suspension actually has a little more negative camber gain in compression. It still not as much as an early suspension, I'll bet. ;) I wonder why GM decided to decrease the camber gain in 1988 or if it was a consequence of a lowered roll center.

[chevynut]

Where are the three triangle pattern bolt holes relative to axle centerline? I can add that too. Stock

I gave you the center of the inner pivots and the bottom holes are 1 7/8" below that.

[NickP]

So, I took the GM drawing and got it to the correct scale and lookin at it, I noticed the half shafts appear to be down a pinch. I assume, this drawing represents and actual loaded car, drive and fuel.

http://pic20.picturetrail.com/VOL1600/2283636/23877721/412885314.jpg

[55 Rescue Dog]

I am still trying to figure out how positive camber gain can be a good thing in rebound on the outboard wheel coming off a bump in a corner. Isn't that what can contribute to a hard to recover "snap over steer", or jacking condition? Just autocrossed my C5 last Sunday, and had to recover an over steer from going too fast a couple times, but was able to catch it, and bring it back in line. It is really a pretty forgiving car when pushed too hard. I just wonder how the C4 would react under the same conditions, and that was not from a bump in the road, which is a whole different scenario.

[chevynut]

I am still trying to figure out how positive camber gain can be a good thing in rebound on the outboard wheel coming off a bump in a corner.

Well, you can't have your cake and eat it too. You have to think about what ALL the tires are doing. To improve traction on the INBOARD tire you want positive camber, even though it's partially unloaded. The consequence of that is that if your outboard wheel goes much below ride height, you lose your negative camber. But how often does that really happen in a hard turn? Also, remember that you start out with about .5 degrees of negative camber at ride height so you have to go below ride height just to get zero camber.

[55 Rescue Dog]

I don't think the C4 IRS is exactly light years ahead of the Corvair, C2, or C3. Since the axel is still the upper locating link, it still move in an arc, just like the Corvair, just a lot less. It seems to be just a double jointed swing axel, which is one reason why GM had to lower the rear roll center, and static negative camber. And, if you narrow the rear it makes all the arcs move even more you said. If anything the rear should be wider. Toe angles changes are critical for stability too.
Here's an interesting read on Chevys first attempt at an IRS
http://ateupwithmotor.com/model-histories/chevrolet-corvair-history/3/

This is interesting too.
http://www.rqriley.com/suspensn.htm

[NickP]

I don't think the C4 IRS is exactly light years ahead of the Corvair, C2, or C3. Since the axel is still the upper locating link, it still move in an arc, just like the Corvair, just a lot less. It seems to be just a double jointed swing axel, which is one reason why GM had to lower the rear roll center, and static negative camber. And, if you narrow the rear it makes all the arcs move even more you said. If anything the rear should be wider. Toe angles changes are critical for stability too.
Here's an interesting read on Chevys first attempt at an IRS
http://ateupwithmotor.com/model-histories/chevrolet-corvair-history/3/

This is interesting too.
http://www.rqriley.com/suspensn.htm

Here's what I fail to understand. You, continue to bash, distrust and argue any good that any C4 equipped chassis provides and yet, you have one....................................... Odd, don't you think? So, it's apparent that you just argue for the sake of arguing. http://www.trifivechevys.com/showthread.php/4594-Picked-up-my-new-C4-chassis!

[chevynut]

I don't think the C4 IRS is exactly light years ahead of the Corvair, C2, or C3. Since the axel is still the upper locating link, it still move in an arc, just like the Corvair, just a lot less. It seems to be just a double jointed swing axel, which is one reason why GM had to lower the rear roll center, and static negative camber.

On any suspension the tire rotates around the IC of the suspension links. The Corvair has very short swing arms and the camber changes dramatically as a result. Any suspension that has the IC on the opposite side of the car will behave as a "swing arm" but with a much longer arm, the length of which is determined by the angle between the links. The consequence is that in bump you get negative camber gain, and in droop/rebound you get positive camber gain. The further out the IC is, the less camber change you get. Static camber has little to do with it.

The wheel/tire rotate around the IC in any case as if it was a solid swing arm, whether it's a front or rear suspension, Corvair, C2, C3, C4, C5, C6 or C7 Corvette. The a-arms at the rear of the C5/6 behave just like the halfshaft and strut rod in a C4 rear. The front A-arms on any IFS behave the same. Is that what you just can't understand? You don't seem to understand how any of this actually works.


And, if you narrow the rear it makes all the arcs move even more you said.

We showed that narrowing a C4 rear by 3" has minimal impact on suspension geometry and I can easily modify the location of the IC with a strut rod bracket hole relocation. If I move the hole down I could move the IC back out to where it was stock...it would take a very small change and the suspension would behave the same as stock. I could put the IC wherever I want. But even as it is, the IC further out than the early C4. Some people say the early C4 geometry is actually better than the late C4.


If anything the rear should be wider.

Sure, cut out the quarter panels and you can make the rear as wide as you want. Isn't that what you said you were going to do? :D :p To put a wider tire on you have to narrow the rearend or let them stick out of the quarter which would look stupid. Wider tires are good, aren't they? So are you planning to leave a 3" gap between the top of your tire and the bottom of the opening to account for suspension movement? LOL! :D I don't care what hacks you make on your own project, but my quarters aren't getting cut.

I explained why I narrowed the rearend...it was to enable fitting larger tires. You can't go over about a 295 without doing that or cutting sheetmetal. Which part don't you understand? Wider tires are better, and the narrowed rear geometry is possibly even improved due to the slightly greater negative camber gain on bump.


Toe angles changes are critical for stability too.

No shit? :D So tell us what the toe does on a stock or narrowed C4 rear over 6" of total travel. We've proved that all of your other bogus complaints about narrowing a C4 IRS have zero merit. Get out your pen and paper. :geek:

[chevynut]

Here's what I fail to understand. You, continue to bash, distrust and argue any good that any C4 equipped chassis provides and yet, you have one....................................... Odd, don't you think? So, it's apparent that you just argue for the sake of arguing.

Yeah, isn't that weird? He tries to show that he knows how all this stuff works, but he clearly doesn't, and doesn't know how to do any analysis. He thinks GM got everything perfect and you can't mess with anything or it'll fall apart somehow. He once said he asks questions to learn...he doesn't ask questions, he criticizes any changes and doesn't try to learn, just argue and bash what others do. He probably still believes that a single shear design is always bad, that poly bushings cause binding, and that moving the toe rod down negatively affects the suspension geometry no matter what the facts show. He probably had ADHD as a child....maybe still does.:D

[NickP]

Speaking of the toe rod; What have you analyzed relative to toe change in stock configuration being that the tire/knuckle dogbones rotate in an arch parallel to the vertical plane central of the car while the toe rod is close to 95°?
http://pic20.picturetrail.com/VOL1600/2283636/23877721/412887857.jpg

[chevynut]

I haven't really looked at toe change, but note that the toe rods appear to be parallel to the halfshafts, which are parallel to the strut rods. Ask RD what his analysis tells him. :D

[55 Rescue Dog]

Ironic that the moderators on this site bash, criticize, argue, and INSULT anyone on this site that doesn't agree they are the best automotive design engineers on paper hands down. I have learned plenty from this site, and others, but I didn't realize it was a requirement to accept everything as gospel according to someone that has been selling something that drives perfect in the real world of smooth paper, numbers, and what they have read, or heard, but never actually tried it.
And yes, I'm sorry. The single shear forward dog bone mounts with poly bushings have to be one of the best ideas I've ever seen. I don't think I'm the only one on this site that needs to drill a hole in their navel to see where they are going.

[55 Rescue Dog]

And a special thanks to Cnut for diagnosing me with ADHD!
http://psychcentral.com/lib/famous-people-with-adhd/

[chevynut]

Ironic that the moderators on this site bash, criticize, argue, and INSULT anyone on this site that doesn't agree they are the best automotive design engineers on paper hands down.

First of all, I'm only listed as "moderator" because Sid made me one. I have moderated almost nothing and don't think I need to. I'm just a regular member here like anyone else as far as I'm concerned. I'm sure Nick feels the same way.

Your problem, Keith, is that you don't know how to discuss and debate engineering principles and concepts. I have observed that all you do is question, attack, and ridicule everything anyone does that isn't "factory" correct. You don't know anything about engineering, but like to act like you do. Instead of asking questions to try to understand something, you say things like "I'd love to know how narrowing a suspension improves handling" or other cynical remarks without understanding the users motivation for doing so. Everything to you is "idealistic" and you don't understand or want to understand tradeoffs involved. And when someone explains something to you or proves you wrong, you never acknowledge it, you just hang onto your erroneous beliefs and bring them up a month or two later in yet another snide remark. You've demonstrated this pattern over and over again for months.

I have no issue with debating technical aspects of anything with anyone who posts FACTS, NUMBERS, or whatever to make their case. All you post is opinions, beliefs, anecdotal "evidence" and biased views with nothing to back them up. You don't think anything can be designed or explained by physics or data or engineering analysis, only by actual use. If that was the case, we would have never landed on the moon.

I didn't design the C4 suspension, GM did. You seem to have some sort of twisted issue with it's design, and you think that anyone who dares to try to modify the design to address their specific wants, needs, or improvements is committing some sort of sin. Your comments clearly show that you don't have a clue about how suspensions really work from an engineering point of view. You think coilovers are wrong because they transmit some forces you don't understand, that poly bushings are wrong because they bind, that dropped toe adjusters are wrong....everything that's been done thousands of times successfully is wrong in your mind. But you sit there with a C4 suspension at almost stock height in the rear, and you have no clue where it is in the front. Then you attack and criticize those who try to make theirs work better for them.

If you're too ignorant to even discuss this stuff, and admit when you're wrong, perhaps you ought to keep your mouth shut about what others do. If you have data to prove your point, then feel free to present it and debate the FACTS. Nick and I have worked to present the data to you but you think you're smarter than everyone else. I'm through with listening to your "opinions" based on nothing but your personal biases. There's no point in trying to help someone like you understand suspension geometry or anything else about cars. You already think you know it all.

[chevynut]

So let's hear your positions RD. Tell me why these things are wrong that you've harped on for months and show me data supporting your views....if you can.

You say a single shear design on the C4 dogbones won't work and will fail. Tell me why. Show me the stresses involved.

You say my torque arm front rod end will fail in fatigue. Prove it.

You say poly bushings bind the C4 suspensions. Tell me how, and how they're worse than the stock rubber bushings you love.

Tell me why lowering the rear toe rod the same on the inboard end and outboard end negatively affects the suspension geometry of a C4 IRS.

Explain why coilovers are so bad, and how they're really different than a stock C4 spring.

Describe the detrimental effects of narrowing a C4 rear by some given amount. Show your facts and figures.

Tell me how you'd put a 345 tire under a tri5 with a C4 suspension. What would you modify?

Explain the difference between the early and late C4 IRS designs, and what those differences affect.

Explain how putting the C4 IRS near stock tri5 height is better for handling than dropping it 2-3".

I'll bet you can't do any of these things.:D

[Rick_L]

For anyone who cares to read it, Herb Adams' book "Chassis Engineering" discusses the C2/C3 IRS deficiencies and why the C4 design is better.

[NickP]

http://pic20.picturetrail.com/VOL1600/2283636/23877721/412890005.jpg

[oceangoer]

Chevynut, or Rick_L

Either one of you have the distance from the Rear axle C/L to the Dog bones ?

And, We measured the rear dog bone mounting bracket to C4 frame at 24 degree to Plumb, any comments ?



Michael.

[NickP]

I'm neither but by GM drawing, .77" but I'd ask CNUT

[chevynut]

OG, I'm not understanding what you're looking for. Nick says the inboard halfshaft yoke center is .77" forward of the axle centerline and as far as I know that's correct. I thought it was 3/4" to 1" but have never actually measured it but he has.

I don't know what the 24 degrees you're referring to is all about. The distance between the front dogbone pivots is 4.15" for the late suspensions, a bit less for the earlier ones. I have both brackets and could measure the early one if that matters. I put all of mine at 4.15".

[NickP]

Chevynut, or Rick_L

Either one of you have the distance from the Rear axle C/L to the Dog bones ?

And, We measured the rear dog bone mounting bracket to C4 frame at 24 degree to Plumb, any comments ?



Michael.

Mathematically, it's 21.93° but that's per GM dimensions and a car that is perfectly level in all planes.

http://pic20.picturetrail.com/VOL1600/2283636/5293467/412969671.jpg

[oceangoer]

Chevynut, thanks

Rich, thank you !! looks like we were close. I did finally find the suspension measurements that I misplaced.

We're about to finish the frame rails drawing and get the rails bent soon, The Dog Bone mounting brackets will be mounted on the frame rail rail Kick Up over a 3/8 inch steel plate.

Appreciate the assistance !

Michael.

[NickP]

Chevynut, thanks

Rich, thank you !! looks like we were close. I did finally find the suspension measurements that I misplaced.

We're about to finish the frame rails drawing and get the rails bent soon, The Dog Bone mounting brackets will be mounted on the frame rail rail Kick Up over a 3/8 inch steel plate.

Appreciate the assistance !

Michael.

PM sent

[55 Rescue Dog]

I have been doing C4 conversions on Tri5 cars for over 10 years now. I am a mechanical engineer by profession, and have gained a lot of experience with both early ('84-87) and late ('88-96) C4 Corvette suspensions. My own '56 Nomad has the first conversion I designed and built.

If you have any questions about these awesome suspension conversions, what they entail, how they benefit you, any issues involved, or to help you make a choice between the early or late suspensions, or Dana 44 or 36 rears, please post them here. I'll answer them the best I can.
22 years into the design with zero miles to back it up. I'm just looking at the best solutions to make it better.

[NickP]

22 years into the design with zero miles to back it up. I'm just looking at the best solutions to make it better.

RD, is there a point to your childish banter? At first, I thought you wanted to, well, as you put it learn something but the obvious is that you along with a few others have an axe to grind. For what reason, God only knows. For that, I continue to pray for healing for you. For the sake of this site, which I have no stake in, please discontinue this discourse. Let's all - that reads ALL just stop the childish bull shit, learn to get along or ignore and build your projects. PLEASE!

[chevynut]

GFY RD, I've tried to help you for months with all your "issues" but you're too f'n stupid and/or stubborn to help. Don't bother asking me anything or replying to my threads because I'll just delete your BS. Ask someone else to try to figure out your "problems".

[55 Rescue Dog]

GFY RD, I've tried to help you for months with all your "issues" but you're too f'n stupid and/or stubborn to help. Don't bother asking me anything or replying to my threads because I'll just delete your BS. Ask someone else to try to figure out your "problems".
http://www.trifivechevys.com/showthread.php/4811-chevynut-step-inside

[oceangoer]

Chevynut,

Do you happen to have the measurement of the front lower control arm inner pivot to ground ??

Do you change this height in your applications ?

Thanks,

Michael...

[chevynut]

Chevynut,

Do you happen to have the measurement of the front lower control arm inner pivot to ground ??

Do you change this height in your applications ?

Thanks, Michael...

That dimension should only change with tire diameter. The lower a-arm should be level or slightly high at the inboard end at ride height. That should make the steering rods approximately level too.

[NickP]

That dimension should only change with tire diameter. The lower a-arm should be level or slightly high at the inboard end at ride height. That should make the steering rods approximately level too.

GM drawing shows it parallel with road surface.

[NickP]

Chevynut,

Do you happen to have the measurement of the front lower control arm inner pivot to ground ??

Do you change this height in your applications ?

Thanks,

Michael...

Michael, are you building your own front crossmember? Sounds like it. I have several CAD drawings from the last full chassis I did to include relationships of UCA & LCA & R&P CL. Always glad to assist.

http://www.picturetrail.com/sfx/album/view/23877721

http://pic20.picturetrail.com/VOL1600/2283636/23877721/410659071.jpg

[oceangoer]

Nick,

Good observation. Yes, I'm building another Street Rod and helping two friends with their Tri-5 builds.

I have the front new custom cross members but what I don't have is the actual OEM C4 Corvette lower control arm pivot
distance to ground.

I've tried the G.M. measurement on the bottom of the cross member, but that is very subject to error hence my need for an accurate dimension.

Any assist wold be appreciated.

Michael..

[chevynut]

Michael, I still don't understand the relevance of the height of the inner pivot to the ground. As I mentioned, it's dependent on tire diameter (radius) so it can vary.

If you explain exactly what you're trying to do that might help. I have several C4 suspensions here I can measure if I knew what to measure. If you have one, all you need to do is put a tire on it of the size you want to use, level the a-arm, and measure the height of the pivot.

[NickP]

Nick,

Good observation. Yes, I'm building another Street Rod and helping two friends with their Tri-5 builds.

I have the front new custom cross members but what I don't have is the actual OEM C4 Corvette lower control arm pivot
distance to ground.

I've tried the G.M. measurement on the bottom of the cross member, but that is very subject to error hence my need for an accurate dimension.

Any assist wold be appreciated.

Michael..

Michael I have to concur with Laszlo on this. Even tire pressure can affect that number. Sketch us an idea of what you need and post it.

[Custer55]

I don't know if this will help at all but I have attached drawings of the measurements I took off our 90 Corvette before I started on my project. All were taken with stock size tires and wheels at ride height.
Brian
6715

6716

They are 17x9.5 stock wheels, That is a mistake on the drawings.

[oceangoer]

Yes, I'm well aware of the tire radius effect on the lower control arm and I have the Factory diagram to check. It's a bit tricky to
measure under the ball joint and measure it accurately. I'm just looking for the OEM dim for a starting point. I should have included the current tire radius

The front tire radius is 13 inches, C5 18 inch rim.

Currently the front (late) C4 engine cradle is blocked into place, with the bolts hand tightened. The frame is braced and welded to frame table.

Tire rad 13 inches

lower control arm longitudinal angle is 1 degree.

Lower control arm inner pivot to ground 7 3/4 inch to ground.

Rack outer shaft (to tie rod) 0.5 degree

Upper control arm angle,, not logged yet.

That's all We completed today.

Michael

[NickP]

Yes, I'm well aware of the tire radius effect on the lower control arm and I have the Factory diagram to check. It's a bit tricky to
measure under the ball joint and measure it accurately. I'm just looking for the OEM dim for a starting point. I should have included the current tire radius

The front tire radius is 13 inches, C5 18 inch rim.

Currently the front (late) C4 engine cradle is blocked into place, with the bolts hand tightened. The frame is braced and welded to frame table.

Tire rad 13 inches

lower control arm longitudinal angle is 1 degree.

Lower control arm inner pivot to ground 7 3/4 inch to ground.

Rack outer shaft (to tie rod) 0.5 degree

Upper control arm angle,, not logged yet.

That's all We completed today.

Michael

LCA is 0° but 1° is close. Rack to Knuckle is closer to 4°. What's your CL between the R&P and the LCA?

[Rick_L]

Is 13" the loaded radius of the tire? Or just a 26" diameter tire with no load?

I don't know that it makes a difference for what you're doing but it could.

[oceangoer]

Custer 55,

Thanks for the sketches.

I'd hazard a guess that your tire radius is about 12.750

Your lower control arm pivot for the front pivot @ 7 1/16 and the rear pivot at 7 5/16, it quite a larger angle than I had expected. I was thinking a 1/8 inch difference. But at least We'r getting closer to a solution.

Any idea of the upper control arm angle at rest ??

Thanks !!

Michael..

[chevynut]

Why should there be any angle at all on the lower control arm?:confused: I suspect Custer's car did not have the frame sitting level and has a rake to it for some reason. I noticed the 1/4" difference in the pivots too and was surprised it was that much and it would result in about a 2" rake across the 96" wheelbase. Maybe the bolt-in k-member has some tolerance to it too. The upper dogbone is shown down in front but I don't see any dimensions for the rear height, so that might indicate the rear of the car is sitting higher than it's supposed to. Comments on that Custer? IMO the lower a-arm should be level to the frame front to rear. What would be the purpose of having it tilted if the frame is level?

The UCA angle is already determined if you know the location of the inner pivots. There is a thread here where I compared the stock tri5 suspension to both the C4 suspensions and some of those measurements are there.

Post some pics of what you have so far. :)

[oceangoer]

"LCA is 0° but 1° is close. Rack to Knuckle is closer to 4°. What's your CL between the R&P and the LCA?"


LCA @ "0" degrees, I agree , as too what I've read so far.

RE the Rack, 4 degrees down seems like quite a drop over the length of the outer Rack length.

The front tire radius is Static unloaded. I've been through the un-loaded /// loaded tire diameter rhetoric reading. I'm going to measure the change in tire radius in several Cars ( C4, 2 C5's and '56 210) with close to the same tires to get a better Handle on the Load static drop. Any input would be appreciated. This is provide me with some general data. Then we can adjust....

But as of now this '57 Desoto frame is welded in place on the frame table. a OEM late C4 assembled engine cradle is only setting in place "Blocked" in place at this point. This frame was a Torsion bar and therefore there are no large spring pockets, only a small shock pockets on the outer sides.


Chevnut, I'm not quite sure what your writing here,,,

"The UCA angle is already determined if you know the location of the inner pivots. There is a thread here where I compared the stock tri5 suspension to both the C4 suspensions and some of those measurements are there."

If your meaning that the LCA is level at "0 degrees" longitudinally, then yes "Agreed" the UCA angle is set.

I'll re-read this post and see if I can find your comparison.

The LCA distance to ground is my greatest concern. You all know what this changes in the IRS and not to forget the rack outer links.

[chevynut]

"Rack to Knuckle is closer to 4°. What's your CL between the R&P and the LCA?

Not sure what you're asking.


RE the Rack, 4 degrees down seems like quite a drop over the length of the outer Rack length.

Are you saying that with the LCA level, the tie rods point down at 4 degrees at the ends? That doesn't seem right to me.


The front tire radius is Static unloaded. I've been through the un-loaded /// loaded tire diameter rhetoric reading. I'm going to measure the change in tire radius in several Cars ( C4, 2 C5's and '56 210) with close to the same tires to get a better Handle on the Load static drop. Any input would be appreciated.

I kinda think you're splitting hairs there but IMO the best way to get the loaded tire height is to look at the revolutions per mile on the Tire Rack site for the tire you're going to use. I would say that 1/2" less than the unloaded radius is probably pretty close.


Chevnut, I'm not quite sure what your writing here,,,

"The UCA angle is already determined if you know the location of the inner pivots. There is a thread here where I compared the stock tri5 suspension to both the C4 suspensions and some of those measurements are there."


What I was trying to convey is that if your LCA is fixed and the knuckle is at the proper camber, you can get the location of the inner pivots if you know the height of the bolt holes. I posted those dimensions in the thread comparing suspensions.



The LCA distance to ground is my greatest concern. You all know what this changes in the IRS and not to forget the rack outer links.

I'm still not getting the issue. If you know the loaded tire radius all you have to do is put the center of the hub at that height, level the lower a-arm, and measure the LCA pivot to ground for your application. Same in the rear....with the hub held up at the loaded tire radius and halfshafts level, you know the strut rod pivot height. I must be missing something you're trying to do.

[Custer55]

I didn't have the frame level when I took the measurements, the car was at stock ride height front and rear. I had 9" of wood blocks under each tire so I could get under the car and just subtracted 9" from all the measurements. When I built my frame I set it up with the K member level to the frame as I figured the difference in measurements was due the the rear ride height of the car being higher than the front.
A 275/40/17 tire has a diameter of 25.7" new so a radius of 12.75 sounds about right.
Brian

[Custer55]

Custer 55,

Thanks for the sketches.

I'd hazard a guess that your tire radius is about 12.750

Your lower control arm pivot for the front pivot @ 7 1/16 and the rear pivot at 7 5/16, it quite a larger angle than I had expected. I was thinking a 1/8 inch difference. But at least We'r getting closer to a solution.

Any idea of the upper control arm angle at rest ??

Thanks !!

Michael..

I didn't check the upper angle as it is set by the k member which I didn't make any changes to.
Brian

[oceangoer]

The '57 HT frame has been just sitting again, snow and freezing rain has me stuck at home but the good news is that's were warming up finally. I'm fed up with weeks of below freezing and snow,, rain rain please.....

I haven't yet received a completion date for my new '37 frame rails, but they say I'll know early this next week. Dragging on.. But we finally have agreed on a simple design change and the new CAD files emailed.


RE the R&P. The R&P doesn't have mounts on the new c4 front cross member. That will be done after the frame is finished and basically a rolling chassis.

RE the UCA transverse angle, drivers side to passengers side, is just a matter of curiosity. It would be a nice reference.

RE narrowing the rear sus width. The two sets of wheels, C5 & C6 Corvette with significant offsets. On the mock up We don't need to narrow the half shaft for a narrower total OD. BUT, We might narrow them an extra half inch. I'm using 1 1/4 inch rear control arm offsets from Flat Out, hence I'll have clearance for the C6 rear 19 inch wheels. The toe control arms will be flipped.

SETTING RIDE HEIGTH

Back to the LCA transverse angle, I'm still finding contradictions on this angle. I need some assistance and guidance here so I can move on...


I read that this LCA angle, measured from the pivot point of the lower ball joint to the pivot point of the inner LCA pivot is "0" degrees. This make more sense to me and visually looks very simular to my C4 Vert..

The "Z"measurement procedure puts the bottom of the front suspension cross member, what seems to be too high !! With my car rack tied up I have no means to check my C4's engine cradle high nor the LCA. It would be a nice reference, but prob not reliable.

The front suspension is 100% C4 late suspension components (LCA, UCA, Spindles) on a 2 inch narrowed cross member fab'd by Don @ Flat Out Engineering. Beautiful workmanship BTW.

So, how do I set the correct ride height, exactly.

Michael.



6773

[chevynut]

RE the UCA transverse angle, drivers side to passengers side, is just a matter of curiosity. It would be a nice reference.

Still not sure what you want here :confused:. Are you asking for the angle of the upper a-arm from the balljoint to the k-member? Where do you want it measured, and at what ride height? I would just set the lower a-arm where it needs to be, and wherever the upper one sits is where it sits.


Back to the LCA transverse angle, I'm still finding contradictions on this angle. I need some assistance and guidance here so I can move on...
I read that this LCA angle, measured from the pivot point of the lower ball joint to the pivot point of the inner LCA pivot is "0" degrees. This make more sense to me and visually looks very simular to my C4 Vert..

It's not easy to visualize where the center of the lower balljoint is.


The "Z"measurement procedure puts the bottom of the front suspension cross member, what seems to be too high !! With my car rack tied up I have no means to check my C4's engine cradle high nor the LCA. It would be a nice reference, but prob not reliable. So, how do I set the correct ride height, exactly.

Is that z measurement stuff from GM? If it is, it seems like it should be reliable but it does seem high. Note that it's also for an EARLY C4 since the tires are listed as 255-50VR16. They went to 17" wheels in 88.

Also, why would "Z" increase from shipping weight to curb weight? Curb weight is with full tank of gas, and shipping weight is half a tank. Why would they ship with gas? It doesn't make sense that "Z" would increase at curb weight. Notice it DECREASES in the rear and it's essentially the same measurement.

I just measured my frame jig and I get only 19mm for the "Z" measurement if I'm interpreting it correctly. When I put a level on the top of the lower a-arm where it's shown as level in the drawing (just to the right of the pivot), I measure the a-arm being level and I'm pretty sure the steering arms are level there too. I had some measurements for the UCL and LCL pivot points on the other thread, as well as UCL/LCL lengths and spindle heights.

It seems to me that a line between the LCA pivot and the lower balljoint should be level at ride height. The suspension should work up and down around that. I would just set the ride height where you think it should be :geek:. If that's a 46mm for the "Z" dimension, then set it there. If you want the a-arm level, set it there...that's where I set it. You can always adjust it from there if you want to....as long as you align it at that new height.

[oceangoer]

Yes, I see this suspension drawing is more than likely for the early C4. Is it correct, no idea but I don't trust this drawing.

Agreed, this measurement seems too high.

Yes, The Z measurement changing "shipping to curb weight" is a mystery. Which points to someones home made drawing possibility.

One the snow clears off again, I'll have a few extra pairs on hands and we'll determine the RC "Roll Center" !! I want to keep it high and close to my CG, which is an estimation.

Here's a quote.... There's always a trade off ! But I have a good idea where the RC should be, now I'll check it out the olk fashion way with strings to find out how close.. I would be satisfied knowing that i'm in the mid-range. Most all of the referances show the Roll Center bove the road surface and slightly under the LCA pivot..



Effects of Front Roll Center Adjustment

Front roll center has most effect on on-throttle steering during mid-corner and corner exit.

LOWER front roll center

* More on-throttle steering
* Car is less responsive
* Better on smooth, high grip tracks with long fast corners


HIGHER front roll center

* Less on-throttle steering
* Car is more responsive
* Use in high grip conditions to avoid traction rolling
* Use on tracks with quick direction changes (chicanes)

////////////////

Effects of Rear Roll Center Adjustment

Rear roll center affects on- and off-throttle situations in all cornering stages (entry, mid, exit)

LOWER rear roll center

* More on-throttle grip
* Less grip under braking
* Use to avoid traction rolling at corner entry (increases rear grip)
* Use under low traction conditions
* Increases traction, reduces rear tire wearHIGHER rear roll center
* Less on-throttle steering
* Car is more responsive
* Use in high grip conditions to avoid traction rolling
* Use on tracks with quick direction changes (chicanes)

[chevynut]

With a level lower a-arm, the roll center will ALWAYS be above ground. To raise the roll center the lower a-arm has to point up at the inboard end. Maybe that's the reason for the 46mm "Z" specification in the drawing.

Note that with the late lower rear strut rod brackets, the roll center was lowered and rear camber gain was decreased. The "D" measurement on a late rear should be considerably less.

[oceangoer]

Laz,

Yes, I understand. I'm very close right now. But until We get the frame table set up and AME finishes my frame rails, we're on Project Hold....

I'm only shooting for getting close to the 3.30 RC in the front. I just spoke with Don @ Flat Out and He concurs. Don always marks every front C4 suspension member with the C/L for the axle, I'm as close as I can with this front sus assembly situated on blocks, but it's sitting slickly over 1 degree up on the LCA.. We'll check closer when the frame rails are squared up..

It's also nice to know that the '57 LCA set up height and "0" is correct !! Hope to get that engine cradle tacked in this weekend, maybe welded up.. Soon off the frame table, I need is soon.....

Yes, I've read that info on the rear RC. Goes to show what happens when a design is pushed too fast - one of many changes.

Thanks again.

Michael...

[oceangoer]

Anyone have the dimension from the rear axle C/L to the face of the u-joint Yoke ??

[NickP]

Anyone have the dimension from the rear axle C/L to the face of the u-joint Yoke ??

See #71 in this thread - 14.75"/2

[oceangoer]

I have that dimension. That's the center of the Pinion.

I need the dimension to the face of the face of the U-joint yoke or flange, going forward..

Thanks though

[NickP]

http://pic20.picturetrail.com/VOL1600/2283636/24756197/413106370.jpg

[chevynut]

I have that dimension. That's the center of the Pinion.

The pinion is not in the center of the differential case, it's offset, and the amount of offset depends on whether it's a Dana 36 or Dana 44.

[oceangoer]

NCW,,

YES, that's it

[NickP]

I don't know that I have that dimension anymore. It will possibly be different for the two housings, 36 and 44 but I'm not 100% on that. In the interim, maybe someone has that. I will wade through the 15,000 plus drawings I have - it may take a bit.

[chevynut]

It will possibly be different for the two housings, 36 and 44 but I'm not 100% on that.

Of course it's different between the 36 and 44. We went through that once offline Nick. :) :)

Bot the offset and the pinion length is different between them.

[NickP]

Of course it's different between the 36 and 44. We went through that once offline Nick. :) :)

Bot the offset and the pinion length is different between them.

Good gosh! Do you recall how far back that was?! LOL I have slept a lot since then. In reviewing old notes I am unable to confirm anything. 9.75" sticks in my head but I don't know if that correct much less for which one if it was. CRS is setting in.

[chevynut]

Well I KNOW they're different because we use a different pinion support bracket for them. :) Also you have to change the driveshaft on a C4 Corvette when going from D36 to 44 for that reason. I just couldn't tell you the difference in the pinion yoke locations offhand. And OG hasn't mentioned which one he wants dimensions for :confused:.

[NickP]

I knew the D-Shafts were different along with the aluminum strut and the position of the two holes in the housing but, I am unable to find any of those notes from 7 years ago.

[oceangoer]

Dana 44, of course

[NickP]

Just being curious out loud here, I have seen multiple companies offering extreme duty CV Joint/axle units and some that offer replacement for universal joint applications to CV. Has anyone seen any for a C4? Expensive, I'm sure but some that I have seen (systems) are for upwards of 1200 HP.

[chevynut]

I have seen multiple companies offering extreme duty CV Joint/axle units and some that offer replacement for universal joint applications to CV. Has anyone seen any for a C4? Expensive, I'm sure but some that I have seen (systems) are for upwards of 1200 HP.

From what I know the u-joints are NOT the weak link in the C4 rear, so I don't know how a CV joint would help anything. The u-joints are 1350's.