Stock Tire Chunking PICS
 

I noticed large chunks missing out of both front tires after a practice autocross session yesterday. I was wondering if its time to upgrade to new tires or do these have plenty of life left from a safety and performance standpoint? I started autocrossing this summer and have about 8 sessions on these tires. The only mod is crash bolts for a little extra camber and the fronts are running 0 toe.

Naw, that's just aggressive wear. ;)

The underlying carcass of the tire looks ok. I liked 45psi on the fronts with these tires, I felt like that kept the wear rate reasonable.

What I do see though is a colored band around the tire in the shoulder area, which suggests the tire has been overheated and that could've definitely contributed to what we're seeing. These tires do NOT like heat, if you're not spraying them down after each run then I recommend doing that.

That said after 8 events I'm sure you're sick of these things. If you wanna be all srs bsns you could safely DD these tires and get a second set of wheels for competition-only rubber. If you start swapping wheels on a regular basis you're going to want to invest in the hardened ARP wheel studs, you WILL strip the stock studs.

Thanks for the feedback! I was not spraying them down with water as I thought it was only needed for some of the better rubber people are running. I also think that my current lack of skill( i.e. overdriving) is a major contributor to the heat issue.

Overdriving probably does play into it, but, without video, we can't necessarily pin the issue on that. Those tires kind of force a neat and tidy style. Much more brake, then turn, as opposed to brake while turning. They teach and reward patience. I've got a few events on those things, never sprayed, and that's not occurring with me. For reference, when on the Primacies, I'm down at 33psi up front, and the rears are somewhere between 29-32, depending on what the weather is doing. Being in San Diego, you probably need another pound or so up front because your weather is cooperative, what pressures were you running, and were you trying to keep them at any particular pressure?

I think those tires are mostly cooked from a useful at autocross standpoint, the little bit of delamination on the shoulder in the pic isn't helpful, but I'm not seeing the blue ring on the shoulder that would say you overcooked it severely.

When not on the primacies, I'm on Hoosier A6's. More like a dozen events on those. Much more entertaining, but, I can't echo renfield's experience with the wheel studs. Mine are holding up just fine, no special studs, no open lugs. :shrug:

I took them off and had Bridgestone s-04's put on.

Now I have two good(ish) stock tires I need to sell.

heat management, guys


the tires could have lasted a bit longer, look how much tread there is still.


chunking occurs when you've severely over heated the tire through prolonged exposure or overdriving, both very controllable variables.

Myself and at least two other local autocrossers have had issues. I used to change wheels all the time on my old car with no problems, but within my first year in this car I stripped two studs.

If you ever want to space your wheels out to to the maximum allowed by the offset rule, you'll need the APR studs. Stock studs won't have enough length.

There isn't a blue ring but there is a ring around the tire with a different albedo than the rest of the tire. That strongly suggests the chemical properties of the rubber there have changed.

What tire pressure were you running?

Same thing happened to a set of Pilot Super Sports after about 50 or so autocross runs with my codriver. She was in the overdriving phase in her development so it chunked up the tires a bit. Not a big deal but something we are more mindful of moving forward.

Presumably these are were the front tires. Move em to the rear where it shouldn't wear the shoulders as bad and keep an eye out on them. Or alternatively use these as a DD and then buy another set of tires for autocross.

Same thing happened to a stock WRX at an autocross two weeks ago. No heat management.

-alex

This is what my stock tires looked like after 4 track days with XP10 pads and RBF 600 fluid. You can see they got some heat in them. Unless you are made of money you should back off when you hear tires screeching and sliding.

I then switched to RE11A tires. Can post pics of how they look now after 5 track days but they are in the backseat of the car right now.

http://i.imgur.com/8dcaDoX.jpg

Again, I can't speak to your situation, just commenting that I'm not running into it. Yours and others' experience have reportedly varied. Why is that? Don't know with any real certainty. All I really can say is that after the first season of 16k of DD and regular autocrossing, I'm not breaking things, and I'm not annhilating tires.

As for offset, I'm at +42 when on the 245 hohos, which is full offset for this year. Seems to be sufficient stud length. I may have a mitigating factor, though; I simply machined my old +40 wheels back to that dimension. I doubt the extra single thread exposed is somehow making my studs indestructible, though.

(edit: Had the drive home to let it sink in - yes, if you are using spacers, particularly to hit the full offset from the stock +48, then yes, you'll likely need longer studs. I'm lucky enough to not need the spacers)

I was at 35psi front and 33psi rear. Those are cold pressures at an ambient air temp of about 80 degrees.

I had been using the chalking method where I use shoe polish on the shoulder of the tire and continue to drop pressure between runs until wear reaches the edge of tread.