[GM Kid]

I realize that 400 horsepower underfoot can cause premature wear of the rear tires, but here's an odd scenario.

I'm somewhere around 9,000 miles or so now, and about two weeks ago during an oil change I had my tires rotated for the first time--fronts to back and vice versa.

Today at lunch, I had a co-worker with me who'd always wanted a ride in my car. Dork that I am, I did a tire-squealing launch at one point (just to make her grin) and then performed a lurid, tail-out slide around a corner. Once I got back to work, I got to wondering what I might've done to my rear tires.

So I went out to the parking lot to check, and aside from the fresh black rubber I'd exposed in some spots, I noticed the inner rib on the passenger-side rear tire was fairly smooth. The rest of the tire looked pretty good, with reasonable tread depth. Obviously, this wasn't something I'd just done. It must've gotten that way over time.

Bearing in mind that these tires were just rotated two weeks ago, would you think this weird wear pattern happened when this tire was still up front, or only since its move to the back?

 

[vette68]

Definitely and alignment issue. Happened when the tires were on the front of the car, not in the back. Have someone go over your front end alignment, well have all 4 wheels aligned. But I'll bet your problem started in the front, not the rear...

Does the car pull to one side on the highway on level ground when you let go of the steering wheel?

 

[BigNick]

Sounds like too much negative camber up front wore the inside of the front tires (which are now on the back after rotation).

 

[LRAR05GTO]

What is alignable?

I had my car aligned and the only thing the guy said they could adjust was the toe in the front. I have slight strut rub and my cambers are -0.7/-0.7 up front and -1.1/-1.0 out back.

 

[GM Kid]

Does the car pull to one side on the highway on level ground when you let go of the steering wheel?

As a matter of fact, there is an issue involving the steering wheel--but that gets even weirder. When I had the car in for service two weeks ago, one of the things they did was give me a new wheel. I mentioned in another thread long ago that the leather on my wheel had "etched" (probably from palm sweat--this is Arizona, after all), so I got a new wheel under warranty.

As I've been driving to work the last few days, I've noticed that in order to go dead straight ahead, I have to keep the wheel tipped a bit to the left. Now, that could be normal compensation for the crown of the road (which ordinarily wants to drag you a bit to the right), or maybe it could be that they didn't mount my new steering wheel exactly straight. Don't know. It could even be that I've been "counter-steering" like this for some time, and just never noticed.

I have to go back to the dealer anyway for some unrelated matters, so when I'm there I think I'll point out the worn tire and ask to have the alignment checked. I've noticed that all four wheels on GTOs seem to have a bit of negative camber, tipping in a bit at the top. I can see where that'd cause the inner rib of tread to wear prematurely.

 

[Subdriver]

This may be expected wear. Can someone tell me what the stock GTO alignment specs are?

The spec for front camber on the C5 Z06 is -0.7 +/- 0.5, meaning anything between -1.2 and -0.2 is in spec, with nominal being at -0.7. With front camber near -1.0, and some toe out (also normal on the Z06), you have a condition, by design, where the the inner edge of the front tire is taking most of the weight when going straight, and the tires are not pointed straight, thus that inner edge gets dragged along and results in very rapid wear. FYI, I wore my fronts out on my Z06 in 3,000 miles.

So, why is it like this? Because these settings result in better handling. A tire with negative camber will corner better. Some toe out in front will help turn in and reduce mid-corner understeer. Trade-off: lots of tire wear. On a car like the GTO and Vette, GM has erred towards handling.

That said, as you can see from the above tolerances, if you are willign to sacrifice handling for tire wear, there is quite a range of alignment values. Lower the front camber towards zero and your tire wear will go way down. :cheers