Tire size problem

[TheFlyingBananaSS]

I have zero issues with 305/35 and 275/40

[EMB135Driver]

To be absolutely clear, tire height is not your issue, but is the easy way to express/compare tires. Circumference is the problem....different size tires are going to roll at different RPMs to cover the same distance.....this is what is creating havoc with stabilitrak. Only solution is to get the front and back within roughly 3% percent. In the grand scheme of things a couple new tires of a more comparable size and selling the 2 that are too big/small is the easiest and most effective way to solve the issue

[Norm Peterson]

Originally Posted by EMB135Driver

To be absolutely clear, tire height is not your issue, but is the easy way to express/compare tires. Circumference is the problem....

To get somewhat picky, what you're really interested in here is actual tire revolutions per mile. And believe it or not, two different tires of the same circumference can turn slightly different revs/mile.

Most tires actually take a little over 3% more revolutions to go a mile than the number of revolutions that you'd calculate based on the mfr's listed dimensions (I'm not talking about the nominal tire size designation here). But that 3% is only an average correction; it can vary a bit from there.


Norm

[Vegas Bound]

Doesn't height determine circumference? Or does circumference determine height?

[RJT Impala]

I vaguely recall something about Cir=Diameter X Pi or conversely Cir/Pi = Diameter. Could be wrong since that was 50+ years ago, or maybe "new math" changed the formulas.

[Vegas Bound]

Originally Posted by RJT Impala

I vaguely recall something about Cir=Diameter X Pi or conversely Cir/Pi = Diameter. Could be wrong since that was 50+ years ago, or maybe "new math" changed the formulas.

PI R squared is the area of a circle. Almost 50 years ago.

[CamaroFred]

2 pi r = circumference

[Norm Peterson]

Originally Posted by Vegas Bound

Doesn't height determine circumference? Or does circumference determine height?

Can't have one without the other . . . sort of (when it comes to tires, anyway). Read on.

Originally Posted by RJT Impala

I vaguely recall something about Cir=Diameter X Pi or conversely Cir/Pi = Diameter. Could be wrong since that was 50+ years ago, or maybe "new math" changed the formulas.

Originally Posted by CamaroFred

2 pi r = circumference

Guys, your math is correct for as far as it goes. It just doesn't go far enough here.

What those purely geometric equations do not account for is tire compliances that affect the effective radius (and hence some notional "effective circumference"). Essentially this amounts to tread compression in the circumferential direction as it passes through the contact patch, and is a consequence of "tire carcass construction, tread thickness, number of plies, cord type, cord angle, rubber compound, etc." (I'm quoting from a paper co-authored by Hans Pacejka - a recognized expert in tire dynamics).

As a side note, using the tire radius under load to compute a circumference isn't any better. The effective circumference due to tread compliance typically falls midway between loaded and unloaded circumference answers.


Norm

[LETHAL2SS]

285/35/20 front 315/35/20 rear here, no issues whatsoever.

[Mr2Hard2See]

Well going back a little bit starting from stock size at 245/45/20 equates to a 28.68 size. 275/40/20 = 28.66 therefore 28.67 is the magic size. Sorry for the thread jack but I just want to make sure I will not have issues going up to a 22” tire size.

My question is if I go more than .03 over stock size will the computer go nuts, like front and rear tires going into the 29.xx range? Or I can go to the 29.xx range as long as front/rear tires are with .03 of each other?

I’m looking to add Mrr228 rims in size 22” on my camaro. Playing the numbers game if I chose: 275/35/22 = 29.6 fronts and 315/30/22 = 29.4

That’s only a .02 difference so in theory I hope this combination would work problem free. Guys let me know please thank you

[EMB135Driver]

The size is not the issue.....the difference in size from front to back is the problem.....different RPMs of the smaller and larger wheels throw the computer in chaos.....you can have 4 tiny tires on 14 inch rims or 4 Super swampers on 28 inch rims, but front to back and side to side they have to be about the same total dimension to keep the computer from going nuts.

[Mr2Hard2See]

Originally Posted by EMB135Driver

The size is not the issue.....the difference in size from front to back is the problem.....different RPMs of the smaller and larger wheels throw the computer in chaos.....you can have 4 tiny tires on 14 inch rims or 4 Super swampers on 28 inch rims, but front to back and side to side they have to be about the same total dimension to keep the computer from going nuts.

Thank you for the clarification on that much appreciated.

[Aaron0126]

Height is directly proportional to circumference
The fronts are in the shop having 275 40 20 rubber put on them.
My buddy there is going to return the wrong size tires
No stupidity tax on my snafu
To the poster that asked about the .2" difference. I think you will be fine.
ZL1 staggered sizes have a .5" difference. I think that it's greater than .2"
Check it out yourself tho, don't do what i did lol

[Mr2Hard2See]

Originally Posted by Aaron0126

Height is directly proportional to circumference
The fronts are in the shop having 275 40 20 rubber put on them.
My buddy there is going to return the wrong size tires
No stupidity tax on my snafu
To the poster that asked about the .2" difference. I think you will be fine.
ZL1 staggered sizes have a .5" difference. I think that it's greater than .2"
Check it out yourself tho, don't do what i did lol

actually im going 265/35/22 and 315/30/22 and i just seen this setup on youtube it looks great. plus ive gotten my diameter numbers closer as well. 29.3 fronts 29.4 rear