[QUOTE="G-S"] That implies a lot of inertial forward momentum was converted into downwards momentum, it doesn't mean that 'all of' (as quoted from Nev's comment) will be converted. I'm certain some percentage of forward motion remained (even if minor). G-S[/QUOTE] Swat I meant Geoff, When you get propelled forward by a sudden deceleration, then get impaired in your movement by the head stem and handlebars, there is a sudden deceleration point, when the top half of the torso, keeps going, but the bottom half, namely the legs, are impeded by the aforesaid handlebars, thereby, creating a downward movement of the top half of the body, thus creating a tumbling motion, as mentioned by the aforesaid Theo