John Thompson wrote:
>
> No; the momentum of the bike provides a forward force which
> is resisted by the tire's contact with the ground. This is
> transmitted through the hub to the fork, and flexes the fork
> blades backward toward the down tube.
I don't believe this is true. Well, the rearward force due to rolling resistance exists, but it is vanishingly small (for any speed attainable on a bicycle), compared to the forward bending force caused by the rider's weight and the head angle.
In other words, the fork is always being flexed FORWARD when a rider is aboard, regardless of speed, except when braking. A front brake can apply a rearward force sufficient to overcome the forward force due to rider weight. Note, even hitting bumps/obstacles/potholes, roughly within the size range of bumps we can hit and not crash, causes a forward bending force on the fork. A bigger bump hits the tire higher up, not right at the bottom of the tire, and at some point the bump contact point with the tire is high enough that the force is aligned with the steerer - not forward or backward. Bumps bigger than this cause a rearward bending force, but will usually cause a crash.
This is not a bicycle science list so maybe we should drop this line of discussion - but it does affect our old bikes and helps us understand how and why they wear out, bend and break. I guess Dale will give us guidance if he feels we're straying too much.
Mark Bulgier
Seattle WA USA