If you know you are going over- Tuck in the head- and keep hands on the bars and feet on the pedals. May bruise a bit and depending on speed- some blood may occur.
Most of my falls- In fact all of them- have been on the mountain bike and mostly at speed downhill. I knew nothing about most of them till I found the bike on top of me and something somewhere hurts. In that situation it has been get out of the pedals and carefully move the bits that hurt. If they don't hurt more then get up and inspect the bike- Helmet and clothing in that order. Gotta Get the priorities right.
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How long was I in the army? Five foot seven.
Spike Milligan