To give a sense of the magnitude of these forces, a hub engine with a 12mm axle making 40 N-m of torque will exert a spreading force of slightly below 1000lb on every dropout. A torque arm can be another piece of metal attached to the axle that may consider this axle torque and transfer it even more up the frame, thus relieving the dropout itself from bringing all of the stresses.
Tighten the 1/4″ bolt between the axle plate and the arm as snug as Torque Arm china possible. If this nut is usually loose, after that axle can rotate some quantity and the bolt will slide in the slot. Though it is going to bottom out and stop further rotation, by enough time this takes place 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 lttle bit of play, it could go on properly snug, or occasionally 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 isn’t much of a concern, but 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 smooth against the dropout. If this is actually the case, you will want to be sure to have a washer that matches inside the lip location. We make custom “spacer ‘C’ washer” for this job, although lock washer that comes with various hub motors can often be about the proper width and diameter.
For the hose-clamp unit, a small amount of heat-shrink tubing over the stainless band can help to make the ultimate installation look even more discrete and protect the paint job from getting scratched. We contain several pieces of shrink tube with each torque arm bundle.

However, in high vitality devices that generate a lot of torque, or in setups with weak dropouts, the forces present can exceed the material strength and pry the dropout open. When that occurs, the axle will spin freely, wrapping and severing off the engine cables and potentially causing the wheel to fall correct out from the 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 way of measuring support against rotation. Oftentimes this is sufficient.