# Forces on a Bike Pedal Crank

I am trying to determine the forces exerted on a bicycle pedal crank by the rider so I can analyze the fatigue. I believe that I understand how to conduct the fatigue analysis but I think that the forces on the bike crank are more complicated then I have assumed them to be so far.

I know that the forces from the rider will be treated as alternating forces, but am also trying to determine if non-alternating forces exist. I was thinking that the weight of the crank could be considered a non-alternating force.

So far I have broken up the force cycle into four parts to simplify the problem. I am considering the crank forces when the bike pedal is at the top (0 deg), when the pedal crank is parallel to the ground with the pedal near the front wheel (90 deg), when the pedal is at the bottom of the cycle nearest the ground (180 deg), and when the pedal crank is parallel to the ground again with the pedal near the rear wheel (270 deg). At 0 deg, I am assuming that there is a tensile force on the crank normal to the crank ends. At 90 deg and 270 deg, I am assuming that the tensile force is angled. And that the tensile force is normal to the crank ends at 180 deg. Any suggests on whether or not these assumptions are correct would be very helpful.

Thanks!!!!

At 90 and 270 degrees, the force of that the rider is exerting onto the pedals is *tangent* to the crank.

nvn