Uneven tire wear

[mike f]

I had been experiencing a shimmy in the steering wheel lately when I would be driving 65mph+. Checked the tire pressure and all was ok. Had the wheels removed and checked on a balancing machine and they were pretty well balanced. I did notice, however, that the insides of both front tires was worn considerably more than the outsides. I am running Bridgestone SO3's (which I feel are really great tires) and had not run any DE or autox's on them. They have about 12,00 miles on them. The car was set up-corner balanced and wheel alignment- by a very reputable shop that specializes in track setups. Is this type of wear normal for a 930 or is my alignment out of whack? The car runs dead straight if I let go of the wheel. What gives?

[Joe Bob]

Sounds like an alignment, corner balance and new tires are in order....

[don911]

If it was set up for street/track, it was probably set up with some nag. camber.
My 911 was set up with -0.8 front and -1.3 rear. My street tires (RE730's) were on the track and never made it even close to 12,000 miles.
It's just my guess, but if it was set up with neg. camber/track settings, the tire wear you're seeing is probably normal. It's probably worse on the rears. My friend's turbo look went thru rear pretty quickly with just stock settings.

[adscab]

I had the same wear, extreme wear on the inside of the rear tires, was diagnosed as worn bushings. Had to replace the entire rear control arms but everything is fine now. Not sure if my 1990 C2 Cab has the same suspension as your 930 though.

[stlrj]

Mike,

Have you talked to the shop that did the alignment? Track set up usually means a lot of negative camber which would explain your tire wear on the insides.

Cheers,

Joe

[masraum]

yep, track alignment will wear the insides a ton.

Are your struts in good shape, they could cause/allow a vibration, or some other worn component.

The tire wear however is to be expected. You could take the car back and get a milder alignment since you have not had the car on the track you may want much less neg camber.

[mike f]

The struts, ball joints, tie rods, etc. are in good shape. I was also thinking it was the alignment specs but wasn't sure. I'll be calling the wrench today and see what he says. Is it possible to shave just the outer aspects of the tire to even them out, or is new rubber in my future? The rears don't look too bad so I guess I could get away with just buying fronts.

[Sean Hamilton]

I had a similar issue with my front tires worn to less than 50% on the insides whilst the outsides were down to no less than 80% causing excessive wheel shimmy and road noise. Great in and out of corners though.

Wheel shop diagnosed as excessive negative camber.
After re-setting the camber back to spec I had them remove the directional tires off the rims and swap them over left to right so as to put the outside tread to the inside.
I did this in an attempt to even out the wear and to extend the life of the tires.

Although this corrected the wheel shimmy the downside is unless I'm sweeping through the twisties pretty hard the tires now have less contact area with the road surface during normal commute with the worn tread mainly in mid air.
Tread wear is only now just evening out - after 12 months!
So in my view it's false economy - live and learn.

Now, I'd reckon I'd have been better off leaving them as is after dialling the neg camber back whisker.
Or yes, maybe shave a bit off the outsides so long as re-balancing the wheels afterwards is achievable.

[stlrj]

Sean,

Is it reasonable to assume that when your front tires were new and sujected to excessive negative camber, only the inside treads had contact with the road and the outside edges were mostly suspended in air?

Therefore, wouldn't it be better to leave your settings closer to factory specs and have the entire tread on the road surface contributing to traction?

Joe

[Sean Hamilton]

Yeah I see what you're saying Joe, but no the over spec' neg' camber didn't lift the outside of the tread suspended off the ground.
So I'm speculating that it's the excessive pressure/forces (?) on the inside of the tread that wears it much faster than the outside of the tread.

The inside tread was worn down 50% more than the outside.
So when I swapped them over left to right the now worn outside tread elevated off the road surface.
I don't track my car, so yes - I've got it back to factory spec now.

[stlrj]

Assuming the forces are now more evenly distributed along the entire contact patch in front, have you noticed any difference in grip and handling?

Joe

[Tyson Schmidt]

If you run a lot of negative camber, and are experiencing a lot of tire wear on the insides, you should be honest with yourself and admit that you don't drive the car hard enough to warrant such an extreme alignment setting.

We dial in a lot of negative camber for the track and autocross because the cars are cornered extremely hard, and if we didn't, the outsides of the tires would be destroyed very quickly and handling would suffer.

I recommend a lot of negative camber to people who express interest in performance driving, but there really isn't any way to know just how hard of a driver that person is, and how much of their driving is track versus street.

Or better stated, what percentage of the tire wear is from track or street driving.

I run very extreme alignment settings, but my tire wear is very even. This is because the car gets most if it's tire wear at the track. You can put about 10,000 street-miles worth of wear on your tires in a single track weekend if you really push the car.

Track Junkies know what I mean when I say that most people's perception of 10/10ths is more like 7/10ths at the track.