To give a feeling of the magnitude of the forces, a hub motor 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 can be another piece of metal mounted on the axle that may consider this axle torque and transfer it additional up the frame, hence relieving the dropout itself from spending all 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 sum 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 already be damaged.
The tolerances on electric motor axles may differ from the nominal 10mm. The plate may slide on freely with somewhat of play, it could go on properly snug, or occasionally a small amount of filing could be essential for the plate to slide on. In circumstances where the axle flats happen to be a bit narrower than 10mm and you feel play, it isn’t much of an issue, nevertheless, you can “preload” the axle plate in a clockwise path as you tighten everything up.
Many dropouts have speedy release “lawyer lips” which come out sideways preventing the torque plate from resting smooth against the dropout. If this is actually the case, you should be sure to have a washer that meets inside the lip area. We make custom “spacer ‘C’ washer” for this job, though the lock washer that is included with various 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 steel band can 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 deal.

However, in high electricity 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 motor cables and potentially causing the wheel to fall correct 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 provide some way of measuring support against rotation. In many cases this is sufficient.