Re: js mounted clutch...
I did a lot of head scratching before I came up with a simpler to figure out gearing best for me. First I wanted the crank RPM (cadence) to be around 90-100 (which is comfortable to pedal) when I am cruizing around 25-30MPH, even if I put a freewheel on it. So basically I need to put a 11T to 36T cassette on it and leave the crank gears.
I am going to use some 2 cycle motor (49cc maybe) with a centrifugal clutch, that has no gear reduction. So then I have to get the motor that is cruizing at 4,000rpm or so reduced to the crank speed of 90-100RPM. With a jackshaft I need two reductions, one about 14T to 78T and from jackshaft to crank 10T to 84T.
Sounds like a lot of reduction but I want low geared enough to bum around offroad and something I can peddle assist cruizing around town without the engine screaming or lugging.