Originally Posted by
MikeyMK
Chains and belts are both draggy. I'm surprised to have never seen a crank biting a rim. I'm not saying that driving a rim directly off a crank is a great idea, or offering a solution as to how it'd be geared, just that a box between the crank and rim could work and remove a draggy relay device to the axle. And yet.. nada.
That's an interesting idea assuming for the sake of discussion that you could design a frame and wheel to accommodate it. It got me looking for a refresher for efficiency vs gear size since the "rim gear" would be so large, and came across this old NASA paper
https://ntrs.nasa.gov/archive/nasa/c...9800010132.pdf, for those interested. It's pretty comprehensive, more than I wanted to know.
But the challenge I see is more basic: if you're driving the wheel at the rim, you'll still need some gears in the middle to turn the wheel fast enough and pretty drastic ratios, so you're back to the gearbox anyway. I don't see any way around that.