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 slightly below 1000lb on every dropout. A torque arm is Torque Arm china usually a separate piece of metal mounted on the axle that may take this axle torque and transfer it additional up the frame, thus relieving the dropout itself from choosing all of the stresses.
Tighten the 1/4″ bolt between the axle plate and the arm as snug as possible. If this nut is certainly loose, after that axle can rotate some quantity and the bolt will slide in the slot. Though it will eventually bottom out preventing further rotation, by enough time this happens 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 a bit of play, it may go on flawlessly snug, or sometimes a small amount of filing may be necessary for the plate to slide on. In circumstances where the axle flats happen to be a bit narrower than 10mm and you are feeling play, it isn’t much of an issue, but you can “preload” the axle plate in a clockwise route as you tighten everything up.
Many dropouts have speedy release “lawyer lips” which come out sideways preventing the torque plate from resting toned against the dropout. If this is actually the case, you will need to be sure to possess a washer that fits inside the lip region. We make custom “spacer ‘C’ washer” because of this job, although lock washer that is included with a large number of hub motors is often about the right width and diameter.
For the hose-clamp unit, a small amount of heat-shrink tubing over the stainless band can produce the final installation look even more discrete and protect the paint job from getting scratched. We incorporate several bits of shrink tube with each torque arm package.
However, in high electric power devices that generate a lot of torque, or in setups with weak dropouts, the forces present can exceed the material power and pry the dropout open. When that occurs, the axle will spin freely, wrapping and severing off the electric motor cables and potentially triggering 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. In many cases this is sufficient.