The Crystalyte 404 hub motor is well matched to a 16" wheel. I run one on an old Rebike steel recumbent (front motor) at 48 Volts and it is very fast. I am able to cruise at 24mph on it. The 405 is matched to a 20" wheel, and 406 is matched to the 26" wheel. As noted earlier the rpm/volt varies, and in this case the 404 has 4 windings, which is faster than the 405 which has 5 windings. The 404 has a higher rpm per volt. So the 404 in a 16" has about the same torque as a 405 in a 20" etc., as the higher rpm per volt is offset by the smaller wheel size. I like this motor - I would use an Aotema sensorless controller on it, to avoid issues with Hall sensors in wet environments. The rebike runs great. You need a 100mm dropout width. The motor was tightish on the spacing but had 2mm clearance on either side of the motor, to the forks. Check your engineering diagrams. I also run a 404 on a 16" Bridgestone Sneaker City folding bike.
Last edited by chvid; 11-23-09 at 01:30 PM.