Originally Posted by
kimjon
It has a friction drive. Basically out of the motor, directly connected to the crank is what looks like the knurled handle of a socket wrench. The drive spindle is about 19mm in diameter and the wheel is roughly 190mm in diameter...so giving it roughly a 10:1 gear ratio.
This knurled drive is a direct drive...i.e. no clutch, so when the motor is going, so are you. It's single speed, no gears. The engine should top out at 19,000 rpm (give or take). I haven't done the math, but it will do about 40-50km/h. Doesn't sound fast, but it will get to top speed pretty quickly!
As the tire wears, you can move the tire up to meet the motor which is in a fixed position.
Very simple design. It does have a few negatives, but overall its perfect for this application.