They say to change the ACR hub and bearing every 12 competition hours. Mine busted at 19 hours. Luckily, I decided to take it apart and see why the axle nut had slacked off twice, so no harm done. It broke right at the outside edge of the bearing, so the spline of the outer joint was doing all the support for the wheel. I wonder how long the axle would last before the wheel/brake assembly exited the car in a spectacular fashion?