B: The operative idea is to roll and avoid impact. You can break bones either way but rolling reduces the forces applied. Tucking makes you rounder, roll better and reduces risk of head/neck injury. The problem is that developing a tuck and roll reflex takes a tremendous amount of training. Judo is one way, if you have a year or two, tumbling gymnastics is another, parajump training is a third, horrendously expensive if not government sponsored and it helps to be a twenty something. The problem is even the most reflexively acting rider is still going to have to go into action in a few tenths of a second and tuck and roll is really hard when you are still attached to the bike unless you are endoing. If you catch an unseen root, slick RR track or paint stripe it is all over in 1-2seconds. If somebody hits your front wheel in a group you have a little more time to react but it is really hard to bail off a bike sideways for a tuck and roll. Steve