You may recall I recently started a thread about a slight steering wheel shimmey in my 2001 coupe that starts at about 70 mph, is strongest (although not very strong) at 80, and is gone by 90. EVERYTHING about tire/wheel balance, lateral and vertical runout, steering looseness, bearings, alignment, etc has been checked and found OK. Putting a completely different set of stock wheels and tires on the front does not change the situation. What a puzzle.

My independent shop did mention that the insides of both front tires (Goodrich KD SSS runflats) are showing significant cupping after about 10,000 miles. The previous set of tires (same KD SSS runflats) also did the same and I replaced them after about 10,000. At that time the dealer had checked alignment on all 4 wheels and reset to the middle of the factory spec range- the fronts were within spec but toward the max limit for negative camber, so reducing the front negative camber should have reduced wear (and cupping?) on the inside. Well, it may have have helped a little but obviously didn't eliminate it. The dealer checked the alignment again last month and found it to be normal.

So, the questions:
1. Is the tire cupping causing the steering shimmey, or is the shimmey causing the cupping?
2. How to fix the problem?

Thanks!

 

Jim,

When I bought my Z-28 new in '96, after about 20K miles, I had severe cupping on the outide of all 4 tires (they were faithfully rotated every 6 K miles). I did get 77K miles out of them; could have gotten another 8-10 K but just got tired of the feel in the steering wheel.

They were balanced and rebalanced and never were perfect. Against my better judgement, I replaced them with the same tire (the OEM Goodyear RA's that everyone hated so much).

I had concluded that the cupping problem was mainly from running too low a pressure in the tires, though I followed factory recommendation. The second set held a balance and I ran them about 4 lbs above the factory recommendation.

In my situation, that set showed no signs of cupping. I replaced them after 75K miles of trouble free service. I don't know how much of the problem was pressure related and how much may have been something wrong with the first set of tires. In my own mind, running the higher pressure was the solution.

Good luck.
Mark

 

I hope you get some helpful answers, because I have the same inner tire wear that you have. I got 40K out of them, but the inside edge of each front tire was terrible. Alignment was "within GM specs" on two tries over that time! I don't want this to happen to my new tires. :smash: I suspect your "shimmy" is from the tire wear, and not the other way around.
:rolleyes:


[Modified by carpe dm, 11:54 AM 7/4/2002]

 

This seems to be a standard problem with Corvetts. I have found that having a Chevrolet dealer align the car never seemed to solve the problem. My solution was to find a good independant alignment shop that would take the time to do it right. Finding such a shop is not easy but well worth the time. Usually you find it by word of mouth from other 'car guys'. I am on my third set of Goodyear EMTs with just a tad over 222K miles on my '99 coupe. With the amount of driving I do, I wouldn't risk driving without the run flats.

 

This is an interesting thread because my C5 is the very first vehicle I have owned where the front tires have not cupped. :D

 

I concur completly! My experience has been the same. Anyone in the D.C, MD, NOVA, area who wants a reference to an excellent allignment shop in Woodbridge, VA E-mail me and I'll reply with the info.

 

This must be a mis-type. Nobody can get 222K miles on three set of tires on a C5. :nonod:

 

I noticed in your sig, you are running Bilstein Sport shocks. I have lowered my '98 to the limit of the front bolts and matched the rear to the front. I am also running the same shocks with no unusual tire wear. I said that to say, cupping of tires are largely due to shock absorbers.

Hope you solve the problem. Good luck.

 

Correctamundo! Cupping is almost always a result of weak shocks.

 

I am impressed with your 222K on a 1999 Coupe. How has the car held up and what kind of maintenance have you perfomed? You have processes lots of fuel and Moble One dollars. HiHi

I just started a new topic on this subject at
http://forums.corvetteforum.com/zerothread?id=335935




[Modified by Dick Kriss, 3:24 AM 7/5/2002]

 

Thanks for the replies.
1. I dont think that the problem is tire pressure or weak shocks- I set the tires at 32 psi cold in the morning, with a good gauge and of course, the pressure increases as the day gets warmer. The Bilstein Sports are supposed to be a bit stiffer than the stock Z51 shocks, and they feel like it. Having both front shocks go bad immediately seems unlikely.
2. The next plan is to get an alignment from a good shop outside of the dealer, well see what that does.
3. Is it practical to spin the wheels and sandpaper the inner tread row to eliminate the cupping? Otherwise I wont know if the alignment stopped the problem.....

 

Gearhead, I don't think using a different shop will make nearly as much difference as using different alignment specs will make. Here's an old post of mine and my tires are very even now.

Here's my thoughts on alignment. I too had tire wear problems and was running on my third set of front tires by the time I acquired enough information about the C5 alignment to get things figured out, (I think). I set my own alignment in my home shop so I can try lots of settings with little expense.
First off, keep this in mind, you're driving a high performance car and a little aggressive tire wear is not out of line for a performance car running neg. camber, which is necessary to attain the cornering G-force ratings GM advertises.
According to GM document #776629, which gives alignment specs for the C5 & Z06, the (Preferred Front Camber is -.20 degree) for the C5 with FE1 & FE3 suspension. The (Camber Tolerance is +/- .50 degree). So if your front camber is anywhere between (-.70 degree to +.30 degree), you are within GM specs. You hardly need an alignment machine to get camber within that tolerance, that's easy hand level and eyeball range.
The Good Year run flat tires have a wide, square shoulder tread and a very hard sidewall which will put much more pressure on the edges of the tread, due to a small camber angle, and will result in what seems to be aggressive tread wear on the edges of the tread, usually the inside due to the neg. camber. Non-runflat tires have a much softer more compliant sidewall and is part of the reason the Z06 runs more negative camber.
The more square (0 degree camber) you set a wide tread tire, like the runflat, with the road, the less abnormal tread wear you will see.
I think it would be a wise move for GM to provide a set of "performance specifications" for aggressive driving, and another set of "touring specifications" for normal highway driving. They would need to provide a brief pro & con statement of the two specs and let the driver decide which way he wants his car set up.
So, back to the question as to what to use for good tire wear. Following is what I am currently running and with 11000 miles on the Stone RFT’s , there is no measurable wear variation in the tread.

Front
Camber: 0.0 degree, (error to the pos. side less than .10 degree if not exactly 0)
Caster: 5.0 degree, (steers a little easier and not nearly as important for street as it is for performance)
Total Toe: 0.1 degree pos.
Rear
Camber: 0.0 degree, (error to the neg. side less than .10 degree if not exactly 0)
Total Toe: 0.0 degree to neg. 0.1 degree

 

Alan-
I think you are correct about the alignment issue. Unfortuntately, my front camber was reset to 0 last Fall, before this set of tires was installed. So I can't gain anything there, and the toe is pretty close to 0. Any other ideas?

 

Any chance that a wheel bearing may have gone south?

 

Mitch-
A good thought, but the dealer beat you to it. New front bearings last month, no improvement.

 

I too found that a bad shock (on the Driver Side) happened to be the cause of cupping on my front tires. Has something to do with "bounce steer". In effect, if one wheel (or both for that matter) doesn't stay firmly planted on the road, the up and down action of the wheel will cause the other wheel to shimey right and left, thus the cause of cupping! New shocks solved my problem.

 

Aside from leaks, how can I test the shocks while they are still on the car?