To give a sense of the magnitude of the forces, a hub electric motor with a 12mm axle making 40 N-m of torque will exert a spreading force of slightly below 1000lb on each dropout. A torque arm is certainly another piece of metal mounted on the axle which can consider this axle torque and transfer it additional up the frame, as a result relieving the dropout itself from spending each of the stresses.
Tighten the 1/4″ bolt between your axle plate and the arm as snug as possible. If this nut is usually 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 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 could go on perfectly snug, or occasionally a little amount of filing may be necessary for the plate to slide on. In circumstances where in fact the axle flats will be somewhat narrower than 10mm and you are feeling play, it isn’t much of an issue, nevertheless, you can “preload” the axle plate in a clockwise route as you tighten everything up.
Many dropouts have speedy release “lawyer lips” that come out sideways and prevent the torque plate from sitting down flat against the dropout. If this is the case, you will need to be sure to have a washer that suits inside the lip spot. We make custom “spacer ‘C’ washer” because of this job, though the lock washer that comes with various 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 steel band can produce the ultimate installation look more discrete and protect the paint job from getting scratched. We include several pieces of shrink tube with each torque arm bundle.
However, in high power devices 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 electric motor cables and potentially causing the wheel to fall correct from the bike.
In most electric bicycle hub motors, the axle is machined with flats on Torque Arm china either side which key into the dropout slot and offer some way of measuring support against rotation. Oftentimes this is sufficient.