My $.02 worth: chains and sprockets do a great job IF you maintain them and replace them when needed. If you don't, a chain failure can be anything from simply peeling off the sprocket onto the road, to violently wadding up into the drive sprocket, locking up the rear tire, smashing inner primaries or similar parts, etc. I watched my pal take a vicious crash on his Ironhead Sporty when the chain failed as he was leaning into the I-95 on-ramp. High sided him right off the embankment. Was it his fault? Probably. It's like the FAA crash analysis reports; they virtually always blame the pilot if the engine fails for not noticing a potential flaw before leaving.