Ive heard about the axles bending on the Z's, so I check mine all the time but its fine. Ive heard its been on the chain side, so I check the chain tension. And Ive heard that the chain has come off with medium riding, so I also check the chain tension for that. All I know is that I dont want my axle to bend, and Im not sure if its a factory defualt in the axle, or just a few axles.