austintipton

Hey All!

I just had an awesome track day at COTA, but ran into an issue I'm still trying to figure out. After two sessions, or ~20 laps, I was in a corner under high load and all of a sudden my steering wheel was shaking like I was running over bumps. From that moment forward, any hard lateral Gs resulted in this feeling.

Getting out of the car, I asked someone what they thought it could be and they pointed out that my sidewall was worn about halfway down now. For the next session, I bumped up the tire pressure 3 psi, but the issue persisted.

My best guess is that I ran too low a tire pressure and permanently wore down the sidewall. If I would have had a higher tire pressure, this wouldn't have happened. I started the day running 38 psi and ended at 41 psi. (The hot pressure was 5-8 psi more)

Anyone experience this before? Once you roll a sidewall is the tire toast? Or should I have gone up to a cold pressure of 45 psi and the issue would have gone away?

MB Marko

you'll probably have better luck with this question posting it in the w204 AMG section

austintipton

Whoops! Thanks. I don't see a way to delete this thread.

Kent Seaton

Depending on the tire and speed rating of the tire, you should bump up cold rating at least 5psi if you are clocking over 100mph. On a hard roll, some tires can break down internally if the tire isn't rated for the lateral preassure. When I was doing SCCA B spec, this happened on one of my cars. I upped the speed rating on my next set of tires from an S rating to a V rating. Granted the car could barely ever make it to 130mph even on the salt flats, but the suspension was geared for extreme cornering. The tire I used was nearly identicle, soft grippy type using 35 series sidewalls with a 10mm stretch.

Just curious, what tires and size spec are you running?

austintipton

I'm running Pilot Super Sports with the following....

Size 235 /40 R18 95Y XL BSW
Load Range XL
Speed Rating Y

I had no issues doing 140MPH+ with the tires in a straight line. I'm not sure how to check what lateral rating a tire has.

Kent Seaton

Pilot super sports are fantastic tires. There really is no way to check a lateral rating, It is generally tied to the ply of the sidewalls. The speed rating does have a little bit of information as the higher the speed rating the more stiff a sidewall needs to be. If you want a good tire for short course, go with a lower mileage higher speed rated tire. They will have better grip, just not last nearly as long as some of the sport touring tires. If you are serious about getting further into track, you should look at a set of Toyos on some lightweight rims. I used to be sponsored by SportMax (now known as XXR) which had a decent lightweight option, I don't think they have a 5x112 bolt pattern option though.

Tikiman12

That's called understeer.
You have to slow down before you turn, carry momentum into and accelerate out of the turn.

You're exceeding the tires grip. Slow down just a bit more before entering the turn.

On a c5 z06 vette, we run 33f 36r psi on pilot sports. I forget the exact tire size.