I have a short wheel base recumbent bike (not a trike) with a 16" front wheel and a 26" rear wheel.
Is it practical to put a hub motor on the 16" wheel? Several companies offer this but will a motor in a 16" wheel give me as much speed as putting the same motor in the 26" wheel? Will the motor be able to speed up enough in the smaller wheel to compensate for its smaller diameter?
I am looking at 36 volt 300 to 500 watt motors.
I would like to put the motor out of the way in the front wheel so I wouldn't have to monkey with the bikes 21 gear speeds.
"...but will a motor in a 16" wheel give me as much speed as putting the same motor in the 26" wheel?"
All else (voltage/motor/controller) being equal - NO.
"Will the motor be able to speed up enough in the smaller wheel to compensate for its smaller diameter?"
Not unless you raise voltages but your controller/motor may not handle the changes.
Hub motors will deliver different RPM/Voltage - depending on manufacturer and design. Phoenix series come in 3 varieties which offer different speed/hill combinations for given voltages applied to your design. I'm sure every maker has their specs - you should spend time qualifying what you're trying to acheive from your ride. Will you have enough weight over your front wheel for traction? Up to 500W motors should not be a problem but get into the big boy stuff and you might spin going up hills?
Some guys like to put fast motors in smaller wheels to acheive better hill climbing capability at the expense of top speed, of course. Voltages/controller being equal, of course...
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.
Wonderful feedback, thank you guys very much. I live in Phoenix, AZ and the bike shops are hostile to electric bikes. Two sets of engineers are "thinking" of going into the electric bike business but they only talk to other engineers. The fellows in the local Electric Auto Association are helpful after I get them down to my level of engineering knowledge and several of them have converted bikes. With your help I will be able to ask better questions.