To give a feeling of the magnitude of the forces, a hub engine with a 12mm axle creating 40 N-m of torque will exert a spreading force of slightly below 1000lb on each dropout. A torque arm is Torque Arm china definitely another 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 currently taking all the stresses.
Tighten the 1/4″ bolt between your axle plate and the arm as snug as possible. If this nut is definitely loose, then axle can rotate some amount and the bolt will slide in the slot. Though it is going to bottom out and stop further rotation, by enough time this occurs your dropout may currently be damaged.
The tolerances on electric motor axles may differ from the nominal 10mm. The plate may slide on freely with a lttle bit of play, it could go on flawlessly snug, or in some instances a tiny amount of filing may be necessary for the plate to slide on. In conditions where the axle flats happen to be a little narrower than 10mm and you are feeling play, it isn’t much of a concern, nevertheless, you can “preload” the axle plate in a clockwise way as you tighten everything up.
Many dropouts have speedy release “lawyer lips” which come out sideways and prevent the torque plate from relaxing flat against the dropout. If this is the case, you will want to be sure to have a washer that matches inside the lip place. We make custom “spacer ‘C’ washer” for this job, though the lock washer that is included with a large number of hub motors can often be about the right width and diameter.
For the hose-clamp version, a small length of heat-shrink tubing over the stainless steel band can produce the final installation look even more discrete and protect the paint job from getting scratched. We involve several bits of shrink tube with each torque arm offer.

However, in high ability systems that generate a 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 causing the wheel to fall right 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 provide some way of measuring support against rotation. Oftentimes this is sufficient.