Torque arms are not optional: how a hub motor spins out of a dropout

A hub motor puts its torque into the axle flats, and the axle flats push on the dropouts. Aluminum dropouts, especially on a front fork, can round out and the axle spins, ripping the phase wires and sometimes dumping you. Steel frames are more forgiving but still deserve one.

A torque arm is a $15 to $30 steel plate that grips the axle flats and bolts or clamps to the frame so the torque goes into the frame instead of the dropout edges. Two for anything over 500 W or any front motor. Fit it so the arm points in the direction that resists the axle's rotation under power (and under regen if you have it, which is why two-sided ones exist).