Originally Posted by
SquireBikesalot
I don't understand how the direction of the break is possible if it was a caught squirrel. Wouldn't the fork break in the other direction via the squirrel moving the fork forwards past the breaking point? Unless they were practicing going backwards downhill.
It's simple physics and the power of leverage.
The breaking force is the result of the bike pushing forward while the fork tip is held in place by the friction of the stationary front wheel on the pavement. Normally the fork flexes over it;s length with the highest bending moment at the crown. A squirrel jammed against the back of the blade changes that, moving the fulcrum down onto the blade, which is not designed for those loads, and it breaks back.
The suddenness of the event is also important. In normal breaking the force is applied relatively gradually and the rider has time to get pitched over the bars, and saving the fork. But a front wheel lockup happens much faster, before the rider can be launched, and the G-forces are much higher.
This change in the leverage involved goes beyond squirrels, as people are learning that forks need to be hardened because disc brakes put similarly higher stresses on the blades. (or at least, one of them).