[JshWright]

Without the means or training to manage the victim's airway, there's no advantage to removing the helmet. Leave it for trained rescuers.

[crpatino]

Better yet, become a trained first responder yourself. And urge your family members and colleagues (and anyone you spend significant amounts of time with) to do so as well.

[Xylakant]

By the time a trained rescuer arrives, the biker is dead or has massive brain damage from oxygen loss. So whatever you do can only be better than doing nothing.