MR2 friend tire wear issues... help?, rear tires wear 3x faster than front. Options

[SuperMacGuy]

My friend has a 1991 Toyota MR2 (the second gen, slightly larger and not boxy) version. He has very bad tire wear problems, he is using up rear tires at 3 times the rate of front tires. He can't get more than 5k miles or so. The car orginally came with 14 or 15 inch by 5.5 or 6 inch wheels. He has 16 x 7 inch wheels now. He has the tires inflated to about 38 psi, but his tires show maximum wear on the inner edge, medium wear on the outer edge, and the least wear in the center.
We've both speculated that maybe there is a lot of negative camber in the rear. But we are confused by how the outer edges are worn so much more than the center, given that 38 psi seems awfully high of a pressure for the tire. When I look at his car, it does not *appear* to be overly cambered in the back (but we have not measured it yet). There are no modifications to the suspension.
My friend does NOT autocross, road race, or drag race the car. He does a good amount of 'spirited backroad driving' but I wouldn't consider it to be at 8/10ths or more.
Anybody have any suggestions or know someone that might know more about this problem or how to solve it?

Thanks, Chris

[marka]

Howdy,

The '91 MR2 came with 14x6 front and 14x7 rear tires.

Obviously the alignment needs to be checked. You probably won't get much less (meaning, more positive) camber than around -1.5 deg, assuming everything is in good shape. That's a decent bit of camber, so if you've got toe in (which may or may not be specified by the factory... I think it was), you're going to see some tire wear.

Still, check the alignment. I'd recommend closer to 0 toe in the back and front. Max neg camber in the front (with the stock bolts... Probably -.5 to -.75 will be the max negative). In the rear, go with the minimum negative camber. Stock the cars are 'net build', so don't expect much adjustment with the camber without going to crash bolts.

I _strongly_ suggest that accompanying that alignment your friend get himself either an ST or perhaps an Addco front bar. The '91 & '92 mr2 is known to be twitchy, particularly on throttle lift while cornering. The much stiffer ST front bar balances things out (with the alignment above), even with the crap stock shocks. If he's really into it, you can easily (if you can weld) modify the front bar to allow settings that are a bit softer than the stock ST setting. That'll let you tune stuff if you want to.

In addition, the much stiffer front bar keeps the inside rear from spinning during "spirited" driving. If your friend is doing that regularly enough on the street to affect his tire wear though... :-/

I'd also agree that 38psi sounds high, but not insanely so. I think I'm running 32 psi in the stock 15" streets for our '93.

The inside edge tire wear is where the rears wear out btw... But I can't explain the outside wear. I suspect you'll find that he's running a decent bit of toe in in the back.

Feel free to ask questions... MR2's are something I've been playing with for a while both in ES and as a daily driver. They're awesome cars... :-)

Mark

This post has been edited by marka: Apr 30 2006, 02:05 AM

[Rob Hood]

We had a 92 MR2, and it liked rear tires, too. The wear was not uneven, just much quicker than the fronts. I put Yokohamas (A509 I think?) on and they had great grip. I couldn't get the fronts to wear out though.

[slowTA]

It almost sounds like a worn out bushing, so the wheel switches between + and - camber.