can anyone tell me what the maximum difference in height between the 2 rear tires before it will do damage to the posi? i want to keep a spare (doughnut) in the car for long trips. i have 295/40/18 on the rear - 27.28" high. anyone know of spares tat are that tall with our bolt pattern?

 

I'm not sure that there is a maximum difference in tire size that makes any difference really. The key factor is how long you continue to drive with different size tires. That all depends also upon the condition of your rear end. It won't hurt the axles at all, but the differential will be put to work to compensate for the difference in RPM of the two tires. With that being said I would not recommend driving an absurd amount of miles on two different tires. No sense in causing any damage if you can easily get another tire to match.

 

Goodyear makes a T145/80D18 "convenience" spare, 27.1”, less than 1% difference. Did you calculate your current diameter, or look it up in the manufacturer's specifications for the tire? Actual diameter can differ from the calculated diameter. Should be OK if within 0.1-0.3”. You can get that much difference from identical tires due to inflation pressure.

GY also has a T165/80D17 at 27.6”

Now you just have to find a narrow wheel w/ a 4.75” bolt circle and the correct hub hole.

https://tiresize.com/tires/Goodyear/...ence-Spare.htm

 

thanks for the reply guys. that goodyear T145/80D18 sounds like the one. i have to find a 18"rim that will fit.

 

I suspect most of the 18” wheels will have a 120mm bolt circle, not the 4th Gen 4.75” (120.65mm). Normally, for extended use, I discourage people from bolting a 120mm wheel on a 4th Gen. But with an understanding that it would be a very brief usage, under moderate speeds, it may be the only possible solution.

That would allow you to look at wheels for newer model Camaros, CTS, GTO, etc.

Follow this advice at your own risk

 

i will look into those options. worst case scenario i would have to drive 60 miles. the new camaro spares are 26.5 diameter. would almost 1' difference in diameter cause me a problem driving 60 miles on the highway ? i m looking into the cts / gto sizes. thanks Al

 

The larger the difference, the more wear on the limited slip diff. My thought was a spare 17” or 18” wheel (only) from a late model GM, plus one of the Goodyear tires. Not sure if they use that size spare wheel on any GM models. Then there’s BMW, with 120mm bolt circle.

A quick search shows the CTS runs a 5-spoke 18” x 4” spare wheel, w/ 120mm bolt circle. But the tire is only 26.5”.

What size tire are you running in the front?

 

i have C5 wheels - 275/40/17 on front - 295/40/18 rear. 26.5 is the tallest spare i have been able to find - the CTS and the new camaros. thats app. 3/4 inch shorter. could i drive 50 miles at 50 mph without damage ?

 

Doesn’t anyone carry the 27.6” tire I mentioned and linked above - post #3? Try Tire Rack.

 

that Goodyear convenience spare cost over $200. i found a yokohama 165/80/17 --27.39" that cost $100. need to get a 17" spare and swap the tire. off to the junkyard tomorrow ---