Torque Arm

To give a sense of the magnitude of the forces, a hub motor with a 12mm axle making 40 N-m of torque will exert a spreading force of just under 1000lb on every single dropout. A torque arm is normally a separate piece of metal attached to the axle which can have this axle torque and transfer it even more up the frame, as a result relieving the dropout itself from bringing each of the stresses.
Tighten the 1/4″ bolt between your axle plate and the arm as snug as possible. If this nut is definitely loose, after that 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 takes place 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 lttle bit of play, it may go on correctly snug, or occasionally a little amount of filing may be essential for the plate to slide on. In scenarios where in fact the axle flats are somewhat narrower than 10mm and you are feeling play, it isn’t much of an issue, nevertheless, you can “preload” the axle plate in a clockwise path as you tighten everything up.
Many Torque Arm china dropouts have quick release “lawyer lips” which come out sideways and stop the torque plate from resting smooth 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 is included with many hub motors is normally about the right width and diameter.
For the hose-clamp style, a small amount of heat-shrink tubing over the stainless band can help to make the final 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 power devices 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 happens, the axle will spin freely, wrapping and severing off the engine cables and potentially triggering the wheel to fall correct out of the bike.

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

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