I've been given some yokohama tyres that a friend has used on track during the summer to go on my new 19" wheels, but it looks like a couple of them have got quite hot and picked up a lot of rubber.
I can pick it off with my hands with a bit of effort, but should I just throw these away or should they be ok, I don't really have any experience with tyres that have been tracked. He seems to think they'll be fine and it'll fall off after running them a bit but I'm not so sure. They've still all got about 6mm of tread left so it seems a waste if they are fine underneath, but obviously don't want anything unsafe on and I'll just get a new set of falken/ vreds if not.
Some pictures of the worst one can be found here, I can get some more if needs be:
http://s30.photobucket.com/albums/c316/Gudzy/Tyres/