To give a feeling of the magnitude of these forces, a hub engine with a 12mm axle creating 40 N-m of torque will exert a spreading force of slightly below 1000lb on every single dropout. A torque arm is certainly a separate piece of metal mounted on the axle which can consider this axle torque and transfer it even more up the frame, hence 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 usually loose, then axle can rotate some quantity and the bolt will slide in the slot. Though it will eventually bottom out Torque Arm china preventing further rotation, by the time this occurs your dropout may previously be damaged.
The tolerances on electric motor axles can vary from the nominal 10mm. The plate may slide on freely with a little of play, it may go on perfectly snug, or sometimes a tiny amount of filing could be necessary for the plate to slide on. In situations where the axle flats will be a bit narrower than 10mm and you feel play, it is not much of a concern, but you can “preload” the axle plate in a clockwise path as you tighten everything up.
Many dropouts have quick release “lawyer lips” which come out sideways and stop the torque plate from resting toned against the dropout. If this is the case, you should be sure to have a washer that fits inside the lip area. We make customized “spacer ‘C’ washer” for this job, though the lock washer that comes with a large number of hub motors is normally about the proper width and diameter.
For the hose-clamp unit, a small amount of heat-shrink tubing over the stainless band can produce the ultimate installation look more discrete and protect the paint job from getting scratched. We contain several bits of shrink tube with each torque arm deal.
However, in high electric power devices that generate a lot of torque, or in setups with weak dropouts, the forces present may exceed the material strength 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 right out of your bike.
In most electric bicycle hub motors, the axle is machined with flats on either side which key into the dropout slot and provide some measure of support against rotation. In many cases this is sufficient.