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El 56
01-16-2018, 11:44 AM
Hello Gentlemen,
I’ve been planing on ordering my rear tires for my 56 2 door sedan. Like many, I am try to squeeze the fattest tire under the rear of my car. I have played around with the tire calculator but, knowing that “ALL” cars are different, I made a cheap wheel fitment tool. After measuring twice and again, trying to squeeze the fattest tire under the car, what do you recommend is the minimum safest distance between the tire and rear fender and also between the tire and leaf spring? Thank you all in advance, El 56.

chevynut
01-16-2018, 12:44 PM
I doubt you'll get much bigger than a 275 tire under the car with stock spring location. The cars vary some, but the variances only matter if you're down to 1/8" differences. I personally think you could get by with 1/4" between the tire and spring if that's the very minimum it will ever see. Why would you need any more clearance? The tire can't move relative to the spring. As far as the clearance to the quarter panel, something like 1/2-3/4" should work fine. Also, everything assumes you have the right wheel offset, the axle is centered, and the body is centered on the frame.

The stock wheelwell lips are usually 71 1/2" to 72" wide inside. The springs are 48" wide outside. That's leaves 11 3/4" to 12" per wheelwell for tire and clearances. A 275 is about 10.8" - 11" wide.

El 56
01-16-2018, 12:59 PM
Thank you for the prompt reply ChevyNut. I was asking as I want to get the right offset or backspacing for my rims. As it stands now, I have 3/4” at the drivers side with 7/8” at the leaf spring. On the passenger side I have 1-1/16 on the fender with 5/8” on the leaf spring. This using a 4.25” backspacing on a 8” rim with a 10” tire (255/60/15). I agree with a 275 not working on a stock set up. This is why I want to go with a 255 wide tire.

https://youtu.be/6F7RK0pXkFk

Here is my homemade tool I used. Please let me know if u think I will be ok. Mind you that the 11” flat stock was replaced with a 10” flat stock and remeasurd everything. Thanks.

chevynut
01-16-2018, 01:32 PM
A 275 tire WILL fit a stock setup....that's the calculations I showed. Lots of guys have 275s on their stock tri5 cars.

Looks like your body is shifted to the passenger side a little, ~1/8". Not sure why your axle appears to be off-center a little, but it may just be the variation in the leafs.

You should be able to get a 255 to fit with no problems.

56Mark
01-16-2018, 04:08 PM
I have 245's on 8" rims with zero offset and the clearance between the tire and quarter panel lip is about 1/2". With offset rims I am sure I could have went a little wider. Stock rear axle.

Rick_L
01-16-2018, 04:37 PM
275s will definitely fit with stock springs and stock axle, if the axle and body are symmetrical. I have seen it done in the real world on more than one car. But the clearances are tight and you have to get the wheel offset just right.

The 1/4" difference on your spring to tire clearance from side to side might kill the 275 deal but a 255 should be no problem.

I think a good goal on clearance is 3/4" tire to quarter panel and 1/2" tire to spring (or tub if your spring is out of the way). You can probably fudge both of those a little bit.

El 56
01-16-2018, 10:16 PM
Thank you all for your responses. I will post my findings in a week or so.

JT56
01-17-2018, 01:29 AM
820682078208

Found some old pics of mine with leafs and 275x60x15 mounted on a 8" with 4.25"bs. Fender lips still intact. Now the same setup will not work with a MT drag radial unless you eliminate the fender lip. Tight but wont rub unless your articulate the suspension a bunch.

markm
01-17-2018, 07:25 AM
Back in the mid 70s I had H60-15s on my 56 they were tight, but cleared.

chevynut
01-18-2018, 07:29 AM
An H60-15 is equivalent to a P255/60-15. A P275 is 20mm or about 13/16" wider.

https://www.tirerack.com/tires/tiretech/45_conversionchart.jsp

chevynut
01-18-2018, 08:14 AM
Here is my homemade tool I used. Please let me know if u think I will be ok. Mind you that the 11” flat stock was replaced with a 10” flat stock and remeasurd everything. Thanks.

I noticed you were measuring out at 14" or so....that's not where the tire is widest. I'd come back 2-3" in radius to locate the widest part of the tire.

NickP
01-18-2018, 10:44 AM
https://www.racq.com.au/-/media/racq/image/content-580x360/cars-and-driving/diagram-of-cross-section-of-tyre-541x440.ashx?la=en&hash=6D7FFE031D898A3DFC6FBE9DEC2F6B551DBF7583

55 Rescue Dog
01-18-2018, 04:43 PM
A 255/60-15 would be the safest fit at 27 inches tall, 10.2 overall section width, with 8.2 inch tread width. I think it is a good fit for a tri-five which sits on the same wheelbase as the heavier 94-96 Impala SS which ran the similar dimensions in a 255/50-17. Those were one of GM's best overall performing full-sized cars ever built. And compared to that my 13 Tahoe police pursuit on the same wheelbase even heavier runs a rare size of 265/60-17 tire, and they kick ass, Other than they are government priced at $1600 for a set of 4.

NickP
01-18-2018, 06:46 PM
A 255/60-15 would be the safest fit at 27 inches tall, 10.2 overall section width, with 8.2 inch tread width. I think it is a good fit for a tri-five which sits on the same wheelbase as the heavier 94-96 Impala SS which ran the similar dimensions in a 255/50-17. Those were one of GM's best overall performing full-sized cars ever built. And compared to that my 13 Tahoe police pursuit on the same wheelbase even heavier runs a rare size of 265/60-17 tire, and they kick ass.

FYI, the wheelbase is 115.9 on the Impala and 116 on the Tahoe, much like the one in my garage.

chevynut
01-18-2018, 09:14 PM
WTF does wheelbase have to do with tire size? You put the widest tire on the car for the best performance....that's a 275 on the rear of a stock tri5. Anything less is sub-optimal.

chevynut
01-18-2018, 09:21 PM
94-96 Impala SS which ran the similar dimensions in a 255/50-17. Those were one of GM's best overall performing full-sized cars ever built.

Isn't it amazing that nobody, anywhere, has ever touted the awesome performance of those boats? LOL :D :D

El 56
01-18-2018, 10:57 PM
Good info. Thank you all!

55 Rescue Dog
01-19-2018, 04:09 AM
WTF does wheelbase have to do with tire size? You put the widest tire on the car for the best performance....that's a 275 on the rear of a stock tri5. Anything less is sub-optimal.
It was more of a overall vehicle size comparison, with a couple vehicles that perform well that don't use a 275 wide tire. I couldn't say exactly what would be better performance wise between a 255 vs 275, but besides clearance issues, the 275 is only about 1/2 in wider, but 1 inch taller at 28in , and 3 pounds heavier if that helps a lot for performance.
A 255 tire is close to twice as wide as a "stock" tri5 tire. I like big tires too, but a 275/60-15 is maybe a bit much, and harder to find a matching front tire with similar performance for cornering/braking, I think. Tire construction, and rubber compound are more important than just a small difference in the width.
Is it really necessary for you to act an internet bully, and cuss me out, or anyone else, in so many of your replies???

55 Rescue Dog
01-19-2018, 04:17 AM
Isn't it amazing that nobody, anywhere, has ever touted the awesome performance of those boats? LOL :D :D
If you had ever driven one you would know what I mean. I've had a 95 and 96 Impala SS, autocrossed them both, and they are very impressive for a boat. It would be very difficult to build a tri5 that even come close as far as handling/braking. A C4 conversion chassis probably won't. A tri5 definitely beats it on looks though.

BamaNomad
01-19-2018, 05:58 AM
Isn't it amazing that nobody, anywhere, has ever touted the awesome performance of those boats? LOL :D :D

Actually, at the time, magazines DID tout the performance of the Impala SS .. With the LT1 engine, they ran very well, and the car itself has been a 'collector' car almost from day 1, and still is today; there are Impala SS clubs all over the country (except for perhaps in northern Colorado??).. :)

In 1996, I test drove one for a weekend, and might have bought it except for the 'trunk space', if you can believe that! They put a full size spare in the trunk which reduced the available trunk space to much less than I had with my Intrepid ES, and for a family car which the wife mostly drove, trunk space is important.

markm
01-19-2018, 07:00 AM
http://r.search.yahoo.com/_ylt=A0SO8wW5BmJadGsAICpXNyoA;_ylu=X3oDMTEyZWhtbmU 0BGNvbG8DZ3ExBHBvcwMzBHZ0aWQDQjQ0ODNfMQRzZWMDc3I-/RV=2/RE=1516402490/RO=10/RU=http%3a%2f%2fwww.hotrod.com%2farticles%2fhrdp-1209-94-96-chevrolet-impala-ss-guide%2f/RK=2/RS=P3Sgjds3F_vyv.__AJqeWngC7Ic-

Well apparently someone disagrees with cnut.

BamaNomad
01-19-2018, 07:17 AM
http://r.search.yahoo.com/_ylt=A0SO8wW5BmJadGsAICpXNyoA;_ylu=X3oDMTEyZWhtbmU 0BGNvbG8DZ3ExBHBvcwMzBHZ0aWQDQjQ0ODNfMQRzZWMDc3I-/RV=2/RE=1516402490/RO=10/RU=http%3a%2f%2fwww.hotrod.com%2farticles%2fhrdp-1209-94-96-chevrolet-impala-ss-guide%2f/RK=2/RS=P3Sgjds3F_vyv.__AJqeWngC7Ic-

Well apparently someone disagrees with cnut.

Many 'someones'... :) but don't tell him that! :)

55 Rescue Dog
01-19-2018, 07:41 AM
There are probably better video's but here in one Impala SS. They are a riot to drive for a daily driver.
https://video.search.yahoo.com/search/video;_ylt=AwrC5pbhD2JaUVgA2qT7w8QF;_ylu=X3oDMTBnc GdyMzQ0BHNlYwNzZWFyY2gEdnRpZAM-;_ylc=X1MDOTY3ODEzMDcEX3IDMgRhY3RuA2NsawRiY2sDMTky bWtlbGQ2MTY1dSUyNmIlM0QzJTI2cyUzRDJsBGNzcmNwdmlkA0 tUdDZfVEV3TGpFVWl0UjFXbUNZdmdKdE1qUXVNUUFBQUFETzBp elUEZnIDeWZwLXQEZnIyA3NhLWdwBGdwcmlkA1VEd0FhTlZDUX ppWjFRM0Fucy5kLkEEbXRlc3RpZANudWxsBG5fcnNsdAM2MARu X3N1Z2cDMARvcmlnaW4DdmlkZW8uc2VhcmNoLnlhaG9vLmNvbQ Rwb3MDMARwcXN0cgMEcHFzdHJsAwRxc3RybAMyMgRxdWVyeQNp bXBhbGEgc3MgYXV0b2Nyb3NzaW5nBHRfc3RtcAMxNTE2Mzc2MT E0BHZ0ZXN0aWQDbnVsbA--?gprid=UDwAaNVCQziZ1Q3Ans.d.A&pvid=KTt6_TEwLjEUitR1WmCYvgJtMjQuMQAAAADO0izU&p=impala+ss+autocrossing&ei=UTF-8&fr2=p%3As%2Cv%3Av%2Cm%3Asa&fr=yfp-t#id=3&vid=7cdb86fafd3db6712f5041ef4fd01483&action=view

chevynut
01-19-2018, 09:08 AM
Well apparently someone disagrees with cnut.

Yeah, and that's why they're so popular and in such great demand, right? You can find someone who likes any piece of junk car, even a Mustang II. :D

"The heart of the Impala SS is the LT1 V8, which pumped 260 hp and 330 lb-ft of torque through a column-shifted 4L60 transmission. ""If you’re in the market for a used Impala SS, we’ve found they can be had starting at around $5,000, with well-kept models coming in around $9,000. While 260 hp made them quite a fun ride back in 1994, cylinder-head and cam design have come a long way since then, so you should be able to wake one up nicely with a few bolt-ons, though the LT1, Gen II small-block is a bastard engine with reverse cooling (requiring dedicated cylinder heads) and a front-mounted Opti-spark distributor."

They might have been decent cars in the sea of crap built in the 80's and 90's, but they're still "boats".

chevynut
01-19-2018, 09:21 AM
It was more of a overall vehicle size comparison, with a couple vehicles that perform well that don't use a 275 wide tire.

I guess wider tires don't help, so that's why all the supercars use 205/75-15s right? :D You attempted to connect wheelbase to tire size somehow, which have no connection.


I couldn't say exactly what would be better performance wise between a 255 vs 275, but besides clearance issues, the 275 is only about 1/2 in wider, but 1 inch taller at 28in , and 3 pounds heavier if that helps a lot for performance.

Wider tires have more traction...pretty simple concept. A 275 is nominally almost 13/16" wider than a 255....that's a little over 3/4" (.787").


A 255 tire is close to twice as wide as a "stock" tri5 tire.

No it's not. A stock tri5 tire is a 6.70-15 which is equivalent to a 205/75-15. How is 255 "twice" 205? Grab a calculator.


I like big tires too, but a 275/60-15 is maybe a bit much, and harder to find a matching front tire with similar performance for cornering/braking, I think.

There are thousands of guys running 275s on their cars. Most guys try to run as big of a tire as possible when maximizing performance....it's common sense.


tire construction, and rubber compound are more important than just a small difference in the width.

Given the same tire, the wider one will perform better. That's why sports cars and race cars have such big tires. And the 275 width is .787" or 8% wider than a 255.


Is it really necessary for you to act an internet bully, and cuss me out, or anyone else, in so many of your replies???

So debating and challenging your BS posts is "bullying"? I just asked what ties wheelbase to tire width and you whine about that? You're the one who keeps making snide remarks about everything I post. Go cry to your mommy or grow a pair. :(

chevynut
01-19-2018, 09:25 AM
If you had ever driven one you would know what I mean. I've had a 95 and 96 Impala SS, autocrossed them both, and they are very impressive for a boat. It would be very difficult to build a tri5 that even come close as far as handling/braking. A C4 conversion chassis probably won't. A tri5 definitely beats it on looks though.

Oh sure, a boat like an Impala out-handles a C4 corvette? Gimme a break. The Impala weighs over two tons. The tires are smaller. I'm sure the suspension geometry of the Corvette is superior, and it has an IRS which the Impala doesn't. I guess those things "prove" the Impala will outperform a tri5 with a C4 conversion. Maybe yours.

chevynut
01-19-2018, 09:29 AM
It would be very difficult to build a tri5 that even come close as far as handling/braking. A C4 conversion chassis probably won't.

You must have missed the part where Newman's 57 wagon out-performed a 2010 Camaro in the slalom and skid pad with stock C4 suspensions. And I'm sure a 2010 Camaro could run circles around a 96 Impala boat. And you're right....the Impala is pretty ugly.

567chevys
01-19-2018, 11:04 AM
Hey Guys

This shit slapping back and forth does not help this site ,

Please try to help people so the site Grows .

Thanks Sid

WagonCrazy
01-19-2018, 12:02 PM
Well said Sid. Thank you.

55 Rescue Dog
01-20-2018, 04:17 PM
You must have missed the part where Newman's 57 wagon out-performed a 2010 Camaro in the slalom and skid pad with stock C4 suspensions. And I'm sure a 2010 Camaro could run circles around a 96 Impala boat. And you're right....the Impala is pretty ugly.
Thanks for affirming what I'm hoping for, since I have a "Newman" clone that looks like it should work pretty good with the right suspension/tire set-up with a few other tweaks I have in mind. The one issue I haven't figured out is, how to solve is the wide turning radius using a short wheelbase suspension on a long wheelbase car. Here is an example of another amazing fabricator.
https://www.rrframes.com/

El 56
01-22-2018, 03:28 PM
Gentleman, as promised here are my findings (on my car of course).
with a 255/60/15 BFG Radial T/A tire on a 15x8 rim with 4.25" backspacing my car has about 1/2 on the unrolled fenders and about 3/4" on the leaf springs. Video below.

https://www.youtube.com/watch?v=G4jLZMyEBCw

So if I had 4.5" Backspacing on my rims I'd be looking at 3/4" at the fenders and 1/2 at the leaf springs. A 275/60/15 tire that i wanted is about an inch wider. That would make it pretty close. I don't know if I could say a 275 tire would fit "my car" without rubbing, which I did not want (rubbing issues). It may fit , it may not. But these are my findings if anyone is interested. Thank you all who replied. El 56.

55 Rescue Dog
01-22-2018, 03:55 PM
Good video El 56, and things move around under load. I'll never forget watching a video of Rusty Wallace's car in a NASCAR race years ago,with a camera mounted behind the RF tire, and it looked like the sidewall moved sideways a ton in the corners. I'm going for 255/45-18 tires front and rear which have the same section width with a wider tread.

El 56
01-22-2018, 04:06 PM
I had a 235/60/15 tire under the rear of my 63 Nova and there was about 1/4” clearance of room at the leaf springs and after driving the car around, the tire had a lot of abrasion were it was touching the leaf. Not enough to damage the tire real bad but enough to make you mad that your new tires were not new anymore 😂😂

Rick_L
01-22-2018, 05:23 PM
I am kind of surprised that you have so little clearance. By your numbers you can't get away with a 275 even if you change the backspacing to the more favorable backspace you mentioned.

I've never worked on a 56 but have worked on 55 and 57, and the 275s worked on both. That's puzzling because there's no good reason a 56 should be different.

El 56
01-22-2018, 06:53 PM
Yes, that is why I recommend everyone measure first on their car.

55 Tony
01-23-2018, 03:27 AM
Just a little note about why clearance is needed since some think just not touching is good, around hard turns the tire flexes sideways and I had tires that would obviously rub on the springs at times although standing still it had 1/4" clearance. The shackle around the front half of the spring is where it would rub, so I cut off just the part of the shackle that wrapped around the tire side and left it do it's job on the inboard side.

NickP
01-23-2018, 06:09 AM
Just a little note about why clearance is needed since some think just not touching is good, around hard turns the tire flexes sideways and I had tires that would obviously rub on the springs at times although standing still it had 1/4" clearance. The shackle around the front half of the spring is where it would rub, so I cut off just the part of the shackle that wrapped around the tire side and left it do it's job on the inboard side.

I'm thinking you mean spring slipper rather than shackle. Item "C".

http://www.tampaspringco.com/images/640_leaf_spring.JPG
http://www.tampaspringco.com/parts/leafsprings.html

Rick_L
01-23-2018, 09:57 AM
Terminology. I call it a clamp.

markm
01-23-2018, 11:10 AM
Terminology. I call it a clamp.

That is how I have referred to them in past, when I think slipper in spring lingo I think the 3 leaf example above or F .

55 Tony
01-23-2018, 02:07 PM
Yes I meant the slipper, but I like the word "shackle" better.:) Not sure about "clamp", that makes me think of the actual clamps I made before getting Caltracs.

Rick_L
01-23-2018, 04:25 PM
The shackle is the piece that goes at the rear spring mount that rotates to keep everything from binding. At least to most. You can call the other piece whatever you want.

55 Tony
01-24-2018, 03:23 AM
The shackle is the piece that goes at the rear spring mount that rotates to keep everything from binding. At least to most. You can call the other piece whatever you want.

I must have read someone talking about the shackle in the rear and got it mixed up that way. I'll give a shot at remembering "slider".

El 56
01-26-2018, 02:58 PM
Thought I would add how much bulge a 255/60 tire is wider than the rim.

https://farm5.staticflickr.com/4746/25044787427_0d5b56a593_c.jpg (https://flic.kr/p/Ea85KM)