Bicycle Wheel Introduction
Short Theory of Bike Wheels
Imagine the forces applied to a bicycle wheel--heavy rider banging pot holes, slamming brakes, hammering hills, crashing ledges.
The rim is way too weak to withstand these forces. It's the tension of the spokes that supply the wheel's strength. A bike wheel is like a suspension bridge, suspended on spokes, which are under a great deal of tension.
Think of your wheel under weight. The spokes on the bottom are not totally supporting the weight. The support is distributed to all the rim over all the spokes. The bottom spokes compress a little under the weight, the top spokes stretch a little in direct support, and all the other spokes stretch a tiny bit in support. So, as the wheel rotates, the stress on each spoke fluctuates. It is this repeated tension fluctuation that eventually results in wheels going out of true. Rear wheels are under much greater stress from the torque of power transfer, and they support more rider weight, so they tend to go out of true more often. Of course, violent impact causes a lot of wheel problems. And wheels are not designed to resist side forces, so any non-vertical force can affect true.
Take a metal clothes hanger and repeatedly bend it in one place. It will get hot and break. Flex can cause the same thing to happen to your spokes. To keep your wheel happy by limiting flex, spoke tension must be reasonably high and uniform throughout the wheel.
There's a lot to be said about bike wheels. This subject is separated into these sections: