If you rear-end me in a Taho me while I'm driving my Bronco then I'm probably gonna be safe. If you rear-end me while I'm driving a '80s Festiva then they'll be pulling bit of me out of your grill for weeks. Does my choice of Festiva over Bronco reduce your liability for rear-ending me? No. Until i do something that is illegal (and relates directly to the injuries) and/or so dangerous that it rises to the level of contributory negligence, the car behind is at fault 100% It it was illegal to be without a helmet then things could get tricky, but the majority of fault still lies with the car behind. Then they're talking about comparitive / contributory negligence, no-fault states, mini-tort states, 1% liabilty, 50%, 51% etc... It's ugly from that point. In Ohio if they were required to wear a helmet (M/C novice) then there may be a case to argue that injures that would have been prevented by a helmet should be non-recoverable. That's gonna be an ugly lawsuit though. That must have precedent...?