Hi Mick,

Torque is not a problem, drive belt slip and gearing up are problems I've had.
Gearing up is easy, but belt slippage is more of an issue.
For now, I've solved it, but the belts are a little stretchy and they may slacken off over time?
If you made the gears out of push bike sprockets from the front and back,you'd have it cracked !!
Somthing I may end up doing, but for now, it's all working fine

Replacing the pulleys for bike sprockets is very easy, just turn the pulleys down 3mm and bolt on the sprockets.
You can buy whole new matching bike sprockets (cassettes) and chain from Crapbay for peanuts!