Torque Arm

To give a feeling of the magnitude of these forces, a hub engine with a 12mm axle creating 40 N-m of torque will exert a spreading force of slightly below 1000lb on every dropout. A torque arm is definitely another piece of metal attached to the axle which can have this axle torque and transfer it additional up the frame, therefore relieving the dropout itself from bringing 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, in that case axle can rotate some sum and the bolt will slide in the slot. Though it is going to bottom out and prevent further rotation, by the time this takes place your dropout may already be damaged.
The tolerances on motor axles may differ from the nominal 10mm. The plate may slide on freely with a bit of play, it could go on perfectly snug, or sometimes a tiny amount of filing could be essential for the plate to slide on. In circumstances where in fact the axle flats happen to be a bit narrower than 10mm and you are feeling play, it is not much of an issue, but 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 and prevent the torque plate from sitting flat against the dropout. If this is actually the case, you will need to be sure to get a washer that fits inside the lip spot. We make customized “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 version, a small amount of heat-shrink tubing over the stainless band can help to make the ultimate installation look more discrete and protect the paint job from getting scratched. We incorporate several pieces of shrink tube with each torque arm offer.

However, in high ability systems that generate a whole lot of torque, or in setups with weak dropouts, the forces present may 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 leading to the wheel to fall proper out of 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 provide some measure of support against rotation. In many cases this is sufficient.