Not sure if you guys are aware of the trick to prevent sidewall chunking that I picked up from a local mod driver... when you're done cutting the tire down, go at the edges with a file. I'm not talking about just rounding the edges... you go in at a 45* angle first and grind down until you start grinding the outside rim. You do this on both sides and should see a white line as the wheel spins (if you're using white rims). You then round the foam from there. This creates funny looking tires but it protects them from chunking as the rim takes any hits first.