I slightly cracked one by accidentally dropping the end of a barbell on the rear portion. I used the offending barbell to hold it in place while the epoxy set, and then retired it for good when I crashed the next year. I cracked another one during my encounter with a curb last November. (While cracks do affect the integrity of the polystyrene, I'm not convinced that they ruin the shock-absorbancy for the next hit. But that's a discussion for another thread, not this one. )