To give a feeling 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 just under 1000lb on each dropout. A torque arm is normally a separate piece of metal mounted on the axle which can consider this axle torque and transfer it further up the frame, hence relieving the dropout itself from spending each of the stresses.
Tighten the 1/4″ bolt between the axle plate and the arm as snug as possible. If this nut is certainly loose, then axle can rotate some volume and the bolt will slide in the slot. Though it will eventually bottom out and prevent further rotation, by the time this occurs 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 bit of play, it may go on correctly snug, or sometimes a small amount of filing may be essential for the plate to slide on. In situations where the axle flats will be a little narrower than 10mm and you are feeling play, it isn’t much of a concern, Torque Arm china nevertheless, you can “preload” the axle plate in a clockwise route as you tighten everything up.
Many dropouts have speedy release “lawyer lips” which come out sideways preventing the torque plate from seated toned against the dropout. If this is actually the case, you will want to be sure to get a washer that meets inside the lip place. We make custom “spacer ‘C’ washer” because of this job, though the lock washer that comes with many hub motors can often be about the right width and diameter.
For the hose-clamp version, a small amount of heat-shrink tubing over the stainless steel band can help to make the ultimate installation look even more discrete and protect the paint job from getting scratched. We incorporate several bits of shrink tube with each torque arm bundle.
However, in high electric power devices that generate a whole lot of torque, or in setups with weak dropouts, the forces present can 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 triggering the wheel to fall proper out from the bike.
In most electrical 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. In many cases this is sufficient.