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Interesting marks on tires from Autocross...

Old 09-15-10, 10:36 AM
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Interesting marks on tires from Autocross...

Guys,

My first time to autocross. Up til now, my car has not been trustworthy, and maybe wouldn't pass tech. I roadraced motorcycles some years ago, I've always wanted to autocross. Things got in the way.

I AX'd on plain jane street tires (Bridgestone Potenzas), and it was my first time, and I was the 6th fastest car!

This one section had a (relatively) high speed left, followed by a hairpin left. On these tires, this whole left turn area was a complete slide-fest. This one particular time through there I sort of plowed sideways into the hairpin area. Not like a drift, but more like a snow plow. Neglecting which way is the fastest way through a corner (I don't need a lesson), the right rear had a vibration through it that I've never experienced in a car before. See the attached pictures to see what the result of this vibration was.

The course was mostly left turns, and this is the only tire that this happened to. I think these marks will wash / wear off. I don't care about these marks, the car is not a daily driver.

I'm just curious if anyone has had this happen to them, or seen this before. If the tire is damaged internally, I don't want to AX it anymore, I'd hate to blow it and damage a rim.

Thanks.

BTW. The grip of the tires was not good, but I'm not intending on trying to be the king of the hill autocrossing. I'm just having a bit of fun, so if I kill the tires, I don't care.
Attached Thumbnails Interesting marks on tires from Autocross...-img_20100912_172857.jpg   Interesting marks on tires from Autocross...-img_20100912_172945.jpg  
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Old 09-15-10, 12:21 PM
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What tire pressures were you running that day?
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Old 09-15-10, 01:04 PM
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33 psi, all the way around.
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Old 09-15-10, 02:31 PM
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Try mid 40s to 50 psi. Tires are rolling over onto the sidewall. Higher pressures will help with that, and give better traction all around.





.
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Old 09-15-10, 03:53 PM
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OK, I'll try that next time. I just got through reading about chalking the tires and adjusting the air pressures based on how much chalk wears off.

But the marks are very curious ... I think I could wash the tires and that stuff would come off. It comes off with my fingernail. Which would tell me that the tires are not damaged internally. At least that would be my opinion. But wanted to see if you guys knew otherwise.

I haven't washed the tires because I just put the car away and took the pictures when I got home.
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Old 09-15-10, 04:54 PM
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I doubt you did any actual damage to the tires. Guys give tires like that much worse abuse on road courses.
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Old 09-15-10, 04:58 PM
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Yup. How are your sway bars and bushings. That could be a factor of body roll as well..
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Old 09-15-10, 06:27 PM
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The car had a lot more left. If I could have figured out the meaning of the cones, and had confidence from gate to gate (to not get lost), I could have broke into the 60's I think. That would've put me about 4th. That's darn good. If there were any problems with the bushing or sway bars, I don't think I would've done so good.
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Old 09-15-10, 10:11 PM
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Im guessing this was a concrete track as apposed to asphalt, and I think higher tire pressures would also cure your problem.
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Old 09-15-10, 10:18 PM
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Yes, exactly, concrete. Army helicopter training airfield.
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