wow i did all that work and then i realized that you only asked for just the rider's weight to be included but just so you know that isn't the maximum torque that can be applied to the crank as it is just one of the torques/moments applied to the crank. The definition of Torque is the sum of the torques/moments which are found by Force x radius of each of the forces (rider weight, pedalling force, and gravity) acting on the crank