Tire chunking from last autocross

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Tire chunking from last autocross

Postby EricMarc-Aurele on Tue May 17, 2016 9:00 pm

Hello everyone, after the last autocross when I got home I measured my tread depth (I'm trying to figure out how fast tires wear and extrapolate how much to budget for car fun) while doing this I noticed chunks missing from my front tires.

I have put some pictures up of the worst chunks. https://goo.gl/photos/YefBMhrknRMw8Qbk8
A very small amount of cord is visible in the third picture. The chunks are about 3/32" deep.

From reading other posts in the forums it seems that I'm overheating the tires by understeering and that the solution is: Be smoother and get a 4 wheel performance alignment.
Is this correct?
Will I need to replace the tires before the next autocross to pass tech? (I assume so)
Will a non-stock alignment take me out of the SS02 class? (I think not)
Can anyone recommend good autocross alignment settings for a base 987 Cayman?
Does anyone have recommendations on replacement tires that will keep me legal for SS02? Currently I have Michelin pilot sport N4 tires.

Thank you all for your time, and for being so fun to run with at the events.
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Re: Tire chunking from last autocross

Postby jbrennen on Tue May 17, 2016 11:07 pm

If you can get Michelin Pilot Super Sport tires in a size that works for you, that's a great choice.

I use PSS tires for the street, but I did also run them at the recent PDS both for some demo runs of the skidpad and pitch/catch and for instructor runs. They really hold up to the demands of autocross in a very impressive way. I think I have a few thousand miles on mine plus the PDS activity, and the tires look absolutely amazing. They're also really predictable for autocross.

Another good choice that I've never run, but have always heard good things about, is the Bridgestone Potenza RE-11. They're similar to the PSS in that they are great street tires that will hold up to autocross demands without chunking or other nastiness.

I wouldn't think about something like the Bridgestone RE-71R (which many of the fast drivers are running) until you're routinely placing in the top 25 spots in BRI. They'll really impress you, and they will not chunk on you, but they will wear out quickly. They're also not great everyday street tires -- the ride is very firm, and the tire noise is fairly noticeable as well. Those are really built as a competition tire and everything else is a compromise.
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Re: Tire chunking from last autocross

Postby JayG on Wed May 18, 2016 12:05 am

Another really good tire for street and AX is the Dunlop Direzza Star Spec
Almost as sticky as the RE-71, but should last longer
As long as your tires are 140 TW or higher you are fine in SS02

You can also go up to 20 mm wider than the widest tire that was available on that axle from the factory for your model group (any 987 model), provided you do not increase the track more than 14 mm more than the widest stock track
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Re: Tire chunking from last autocross

Postby Jad on Wed May 18, 2016 8:09 am

Definitely looks like you are overheating the outer edge of the tire. This is usually caused by too much steering input (understeer or push). You need to use the gas pedal to control the direction of the car, not the steering wheel. When you start to accelerate out of a corner, straighten the wheel. If the car is not turning enough, lift a little, don't turn the steering more. My goal at AX was to never turn the steering wheel more than 90 degrees, can't always do it, but never much more.

A good alignment and tires will help hide the symptoms, but be sure you fix the cause of the over heating as well. :beerchug:
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Re: Tire chunking from last autocross

Postby Steve Grosekemper on Wed May 18, 2016 9:01 am

Everyone is correct.
You need a competition alignment (all the negative camber in front and zero toe)
I am actually doing this to a 2011 Cayman as I type this...
Steer more with your foot and less with your hands and the front tire will last longer.
I like the RE-11's best as they really take a beating and have extra rubber where you need it.
That's what's on my street driven 911, and yes you will stay in SS.

Tech says don't bother showing up for the next AX with those tires.
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Re: Tire chunking from last autocross

Postby EricMarc-Aurele on Wed May 18, 2016 9:20 am

Thank you everyone for your advice, it is greatly appreciated. I'll get new tires and an alignment before the next autocross, and I'll work on improving my technique.
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