Originally Posted by
cyccommute
I will point out that you were saying above that there is no lateral flex in the rim. Which is it? The bike has lateral flex or it doesn’t?
It is possible for the wheel to flex easily. However it does not flex in practice because there is no lateral force on it.
Originally Posted by
cyccommute
It’s called cornering. I’m pretty sure that you corner from time to time which hangs the CG out of plane with the contact patch. When I corner, I lean into the corner, away from the contact patch. Now think about that. Where is the CG in that case? Gravity is pulling the CG down and the CG is out of plane with the contact patch. The vector force is angled through the CG but the normal force is still acting on the CG which is a long ways from the contact patch. The only thing keeping the CG from dropping to the ground is the friction of the tires and the lateral force they put on the wheels. This cantilevering of the CG is also what is causing the relatively weak rims to bend out of plane with the axle.
???
When you are cornering the vector of force is traveling to the ground inline with the wheel. Here's an article from ACA teaching people how to ride a bike. They use the terminology "local gravity". In Figure 5 on the right you can see that the force vector is completely in line with the wheel whether you are riding straight or cornering. From the perspective of the wheel it cannot tell the difference.
https://www.adventurecycling.org/def...ring_Heine.pdf
Originally Posted by
cyccommute
Gravity is acting on the CG pulling it down. As the rider leans into the corner, the lateral force on the tires is pushing towards the CG. The lateral force is a fraction of the normal force but still enough to case some flexing of the rim out of the plane of the wheel. Now lets say the rider leans over further to the point where the friction on the tires no longer can hold the bike in the corner. The lateral force on the wheels eventually fails and the wheels slide out from under the rider.
The lateral force does not exist independently. It is only an on-paper mathematical component of the diagonal force vector. The diagonal force is the force which actually exists in reality (the so called "local gravity" in the ACA article). This force is in line with the wheel. The wheel does not experience any force that pulls it side to side. It only experiences a force that is in line with its plane. This force is perfectly capable of causing a slide out despite being diagonal to the ground.
Take a pencil, stand it upright on your desk and place your finger at its top to keep it upright. Now move your finger around so the pencil leans in different directions. Is the pencil experiencing any bending force? No! The pencil experiences only pure axial compression force no matter which way you lean it.
You may be confusing bending with buckling. Buckling is a completely different failure mode that has nothing to do with lateral forces.