To give a feeling of the magnitude of these forces, a hub motor with a 12mm axle creating 40 N-m of torque will exert a spreading force of slightly below 1000lb on every dropout. A torque arm is definitely another piece of metal attached to the axle which can have this axle torque and transfer it further up the frame, as a result relieving the dropout itself from Torque Arm china choosing each 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, in that case 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 takes place your dropout may already be damaged.
The tolerances on motor axles can vary from the nominal 10mm. The plate may slide on freely with a little of play, it could go on perfectly snug, or in some cases a small amount of filing may be essential for the plate to slide on. In conditions where the axle flats will be somewhat narrower than 10mm and you feel play, it is not much of a concern, but you can “preload” the axle plate in a clockwise direction as you tighten everything up.
Many dropouts have speedy release “lawyer lips” which come out sideways preventing the torque plate from sitting toned against the dropout. If this is actually the case, you will want to be sure to possess a washer that meets inside the lip spot. We make custom “spacer ‘C’ washer” because of this job, though the lock washer that is included with many hub motors can often be about the right width and diameter.
For the hose-clamp unit, a small length of heat-shrink tubing over the stainless band can help to make the final installation look even more discrete and protect the paint job from getting scratched. We include several pieces of shrink tube with each torque arm package.
However, in high electricity systems that generate a whole lot of torque, or in setups with weak dropouts, the forces present can exceed the material durability and pry the dropout open. When that occurs, the axle will spin freely, wrapping and severing off the electric motor cables and potentially creating 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 in to the dropout slot and offer some measure of support against rotation. In many cases this is sufficient.