impact throw away the stock foams don't even think about using them. i ran them in my jammin tires anfter 2 practice runs 1 6min. heat and 1 18min. main. my jammin tires still look brand new minus the dirt. but the foam has all but disentegrated in the front tires and completely disentigrated in the rear tires. so now i have a usless set of perfectly new looking tires. and the jamin tires did work great when they had foam in them. at the end of the main the back of my car kept sliding and i couldn't figure out why unitl i pulled off and found out that i was running on flats. use the panther green molded foam inserts i heard those last long enough that you can re- use them when your tires are worn out.