To give a feeling of the magnitude of these forces, a hub engine with a 12mm axle making 40 N-m of torque will exert a spreading force of just under 1000lb on every dropout. A torque arm is certainly another piece of metal attached to the axle that may take this axle torque and transfer it further up the frame, hence relieving the dropout itself from bringing each of the stresses.
Tighten the 1/4″ bolt between your axle plate and the arm as snug as possible. If this nut is normally loose, after that axle can rotate some volume and the bolt will slide in the slot. Though it will eventually bottom out preventing further rotation, by the time this occurs your dropout may currently be damaged.
The tolerances on electric motor axles can vary from the nominal 10mm. The plate may slide on freely with somewhat of play, it could go on correctly snug, or occasionally a tiny amount of filing may be necessary for the plate to slide on. In scenarios where in fact the axle flats happen to be a bit narrower than 10mm and you feel play, it is not much of a concern, nevertheless, you can “preload” the axle plate in a clockwise course as you tighten everything up.
Many dropouts have speedy release “lawyer lips” that come out sideways and prevent the torque plate from sitting smooth against the dropout. If this is actually the case, you will need to be sure to possess a washer that matches inside the lip region. We make custom “spacer ‘C’ washer” because of this job, although lock washer that comes with a large number of hub motors can often be about the proper width and diameter.
For the hose-clamp style, a small length of heat-shrink tubing over the stainless band can help to make the final installation look more discrete and protect the paint job from getting scratched. We incorporate several pieces of shrink tube with each torque arm program.
However, in high power systems that generate a lot of torque, or in setups with weak dropouts, the forces present may exceed the material durability and pry the dropout open. When that occurs, the axle will spin freely, wrapping and severing off the engine cables and potentially causing the wheel to fall proper out of the bike.
In most electrical bicycle hub motors, the axle is machined with flats on either side which key in to the dropout slot and provide some measure of support against rotation. Oftentimes this is sufficient.