To give a sense of the magnitude of the forces, a hub engine with a 12mm axle producing 40 N-m of torque will exert a spreading force of just under 1000lb on every single dropout. A torque arm is usually a separate piece of metal mounted on the axle which can consider this axle torque and transfer it further up the frame, thus relieving the dropout itself from bringing each of the stresses.
Tighten the 1/4″ bolt between the axle plate and the arm as snug as possible. If this nut is definitely loose, in that case axle can rotate some quantity and the bolt will slide in the slot. Though it is going to bottom out and prevent further rotation, by enough time this happens your dropout may already be damaged.
The tolerances on motor axles can vary from the nominal 10mm. The plate may slide on freely with somewhat of play, it may go on perfectly snug, or sometimes a small amount of filing could be essential for the plate to slide on. In scenarios where in fact the axle flats are a bit narrower than 10mm and you are feeling play, it isn’t much of a concern, but you can “preload” the axle plate in a clockwise route as you tighten everything up.
Many dropouts have quick release “lawyer lips” which come out sideways and stop the torque plate from sitting down toned against the dropout. If this is actually the case, you should be sure to possess a washer that suits inside the lip region. We make custom “spacer ‘C’ washer” for this job, though the lock washer that is included with many hub Torque Arm china motors can often be about the right width and diameter.
For the hose-clamp version, a small length of heat-shrink tubing over the stainless steel band can help to make the final installation look even more discrete and protect the paint job from getting scratched. We consist of several bits of shrink tube with each torque arm deal.

However, in high vitality systems that generate a whole lot of torque, or in setups with weak dropouts, the forces present may exceed the material power and pry the dropout open. When that occurs, the axle will spin freely, wrapping and severing off the engine cables and potentially leading to the wheel to fall correct 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 offer some measure of support against rotation. In many cases this is sufficient.