I made about 7 x 40-second runs yesterday in 65º weather on Hoosier A7s and ended up with this on my left rear tire. The course had nearly equal features from right to left, but it seems this was the only tire with any (and excessive) rubber travel. I'm running 36lbs in the fronts and 39lbs in the rears, adjusting between runs. I didn't pyrometer since my camber is maxed out. Stock PASM suspension with -1.4º front, -1.9º rear. But, the rubber travel seems pretty excessive given the circumstances. Any ideas?
I'm pretty sure it's not pick up. The rubber is nearly 1/4" thick in some spots and is fairly consistent around the circumference of the tire. There just wasn't nearly that much rubber to pick up on the course, and I didn't see any 18-wheelers losing their re-treads anywhere in the vicinity.
The driver's side was sitting in the sun on the grid. So, it's possible the tires didn't cool down as much on that side. But, it looks as if the rubber migrated from the outside edge inward.
I have to add another vote for "that looks like picked-up rubber or gunk." I've never seen "wear" that looks like that before. I can't imagine A7s overheating in 65 degree weather at AX. Yea, the A7 is supposed to operate at lower temps than the R7, but it doesn't get much lower than 65 degrees and the short AX sessions should be no problem. I guess there's a slight chance you got a bad tire (it does happen).
If the tire was chunking to that degree you would see cords showing. That picture shows additional rubber on the outside of the tire, not a melted carcass. If it had melted due to extreme heat, you would have left the rubber on the autocross course.
That's an incredible amount of rubber on a single tire. The other three were completely clean. I'm going to bring it to my tire guy to shave. But, I wonder how I could pick up THAT much rubber on a single tire, even if I'm tracking the same line as other drivers?
In 25 years of wheel to wheel road racing I have seen lots of this kind of thing. In road racing, it is typically marbles picked up on the cool-down lap, when the tires are hottest and the speed slowest. It flys off during the next hot session.
Mark the location with chalk. Make another run. See if it has gone from that spot. If it has not, call Hoosier for advice on how to remove it.