I found the foams in my CF MTR broke down kinda quick as well. I wonder if mabye its all that ribbing in them. When the tires squirm its probably scraping up the foam really bad, and over time it will just break down more and more of the foam. I think if Pro-line made the inside of the tire smooth the foams would last a lot longer. For example the inserts in my Werks Lugz have the same amount of run time on them as my CF's do and the inserts have been a lot more consistent since they were new. The inserts in the Lugz are just open cell foams, but the inside of the tires are completely smooth so there is no abrasion on the foam.