j_leder

Spent 3 days at Mid Ohio with Potomac April 29, 30 and May 1st.
The days were cool windy but dry-rained overnight.
I ran brand new Kumho Victoracers in black. I put on about 220 miles for the 3 days. Just had a new 4 wheel alignment and corner weighting on my 1990 C2.

Camber LF/RF -1.0/-1.0 LR/RR -2.0/-2.1
caster 3.7/3/6
toe 0.05/0.05 0.06/0.07

after the 3rd day I noticed significant cupping on the outside edge of both left side tires. Could this be from the grooved concrete? Any ideas??? Please help.
Thanks
Jeff

BrokeAss

Silly question - was it an all right-hand track? Might explain premature wear on the left side. During multi-day events, I like to flip my tires so they're evenly abused.

Cupping can be caused by an improperly balanced wheel. You may have thrown a wheel weight at the track causing the imbalance.

Bull

MO is something like 6 lefts and 8 rights (heavier loads in some rights).

RedlineMan

Jeff;

Cupping is not generally what track tires do. It is more a factor of rubber roll off. Depending on the design of the tread blocks, they can "feather" quite a bit if you are over-driving your suspension settings. This feathering has the leading edge of the block rolled off of rubber that is then deposited on the rear inner edge of the block. This wear sort of takes a 45 degree angle from straight ahead.

Your camber settings are not overly agressive, but perhaps your driving was for them. Soft suspensions also contribute to this, as roll is not controlled very well. Even in the face of some fairly stout camber figures, you can experience this type of wear if roll is excessive.

A little more camer would probably help, and rotating tires is indeed a good idea. I run the same tire at all four corners for that reason.

kurt M

I think there might be something up with the track and how it stresses tires as well. I had 2 different cars come back from MO with the same thing showing on the outer and inner edges of the fronts. One car much more than the other and it showed it to a lesser extent in the back. Looks like a nice even wavy edge all around. Not the saw tooth you often see with too much toe but a gentle undulation all the way around with an aprox 3 inch repeat frequency. I have not seen these phenomena quite as bad as this before. I asked that one of the drivers to bring them to Summit Point this coming weekend and let Paul from Radial Tire read them.

jerome951

I think with the new grippiness of the concrete at Mid-O you are seeing more wear on the outer edges as you corner (likely cornering harder than before), and some dragging effect on the inner edge of the unloaded tire. I was running in black at that event as well and saw a lot of wear on the outer shoulder of my RA1s, especially on the left side.

I used to run Victoracers at Mid-O (before the concrete change) w/ stock alignment settings on my 951. I saw a similar wear pattern on the outer shoulder that Kurt described, almost as if there were bumps under the rubber. I think it's just how Victoracers wear on the shoulders.

You can run the Victoracers in reverse w/ no ill effects except for poorer wet traction, so switching from side-to-side isn't an issue to even the wear among the tires.

I also remember communicating w/ a Kumho engineer who said that the Victoracers require a fair amount of negative camber (e.g. -2 to -3 degrees). If you can't run that much you may want to try a different tire for better wear.

RedlineMan

Hmmm....

I'd say it is a combination of not that much negative camber, the nature of the track, and perhaps that particular tire. For those that have not been there, it seems like every corner there is off camber, some of them quite a bit so. Add to that the autocross nature of having to hurl the car through all the switch backs, and you would surely see high wear rates. I don't think the cement is that big a factor, as it seemed fairly smooth to me.

kurt M

The cement was wet cut smooth using stacked diamond blades that left a flat but ribbed surface that was super grippy when I drove it soon after the work was done. I would 4 wheel drift coming out of T1 and wait for the hook up on the cement. I was placing the car into the corner a wee bit early but with a greater angle of attack when I hit the apex. Slide right over to the the cement, hook up like an F1 on a fresh set of slicks and bingo, great exit RPMs and moving in the right direction. I had to ajust the cars "patch entry angle" as it drove onto the patch as the front end would hook up before the back end was on the patch. Ye haw.

The bumps were far more pronounced than I have ever seen before. (Not that I am a seasoned expert by any measure)

dave morris

Jeff,

I agree with C4Guy ... did you end the weekend with the all the balancing weights in place? If not, that could be the source of the cupping. It's happened to me.

Skip Wolfe

Where the Victoracers shaved or full tread? I would agree with John that its more a function of not enough negative camber than the concrete. From what I understand, Mid-O ground the concrete early summer after they had so many complaints of the concrete that was ground during the Spring was eating tires. I was there in July, and didn't really notice a whole lot difference from how the patches were from years past.

I wouldn't worry about the cupping - shouldn't hurt anything. If it bothers you, you can always flip the tires.

j_leder

Thanks for all your comments.
The tires started as full tread not shaved.
Yes all the weights are still there-since I've had them rebalanced for I go to the Glen end of May.
The car has a cup suspension, but I do feel and see(in pictures) some lean.
I will probably swap left to right-but I didn't noticed any vibration.
Jeff

Bob Rouleau

raacer - outside wear is usually too little camber. Yoou need abouot neg 2.5 to avoid it if you are an experienced driver - with a cup suspension I imagine that to be the case. Cupping is normally caused by imbalance, bad shocks ( enough rebound control) or, something loose in the suspension. The wavy wear pattern may be caused by the ribbed concrete, under load you probably have about 7 degrees of tire slip angle which would be causing the tire to cross those ribs at a small angle - that might produce the appearance of cupping.

Best,

RedlineMan

Ah hah!

The full tread depth blocks will tuck and roll under far more than a shaved tire. This along with the shape of the blocks and the camber settings is probably a large part of why they are worn like that.