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

[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? 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.



C4 front ride heigth.jpg