Torque Arm

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 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 spending all the stresses.
Tighten the 1/4″ bolt between your axle plate and the arm as snug as possible. If this nut is usually loose, in that case axle can rotate some volume and the bolt will slide in the slot. Though it is going to bottom out and prevent further rotation, by the time this occurs your dropout may previously be damaged.
The tolerances on engine axles can vary from the nominal 10mm. The plate may slide on freely with a bit of play, it may go on correctly snug, or in some cases a little amount of filing may be necessary for the plate to slide on. In conditions where in fact the axle flats will be a little narrower than 10mm and you feel play, it is not much of an issue, nevertheless, you can “preload” the axle plate in a clockwise way as you tighten everything up.
Many dropouts have quick release “lawyer lips” that come out sideways and prevent the torque plate from seated flat against the dropout. If this is actually the case, you should be sure to have a washer that matches inside the lip spot. We make customized “spacer ‘C’ washer” for this job, though the lock washer that comes with many hub motors is normally about the proper width and diameter.
For the hose-clamp style, a small length of heat-shrink tubing over the Torque Arm china stainless steel band can make 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 package deal.

However, in high vitality systems 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 happens, the axle will spin freely, wrapping and severing off the motor cables and potentially causing the wheel to fall proper out from the bike.

In most electric bicycle hub motors, the axle is machined with flats on either side which key into the dropout slot and offer some way of measuring support against rotation. Oftentimes this is sufficient.