I haven't seen them ever fail when used as intended (FYI: SM's are in the 2300-2400lb range, turn times faster than most vintage Triumph racers, and they use all the curbing + some on a regular basis), and they're a pretty common wheel. Granted if you hit a 3" wall of curbing head on they're going to break, just as any other wheel would. Take it for what it's worth Bob