20 inch?

GoldenMotor.com

Allen_Wrench

Resident Mad Scientist
Feb 6, 2010
2,784
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36
Indianapolis
1) Depends a great deal on make of bike, if you're talking in-frame. (I've seen pictures, so I know it's been done.)
2) You sure could put a rear-mount engine on one.
3) in-wheel electric motor is probably also an option.