Wouldn't a 1000 Watt BBSHD apply the same kind of pressure on the dropouts? Just coming from the chain instead?flat tire wrote: ↑Oct 13 2018 3:58pmYes. Plenty of people have opened their rear dropouts with hub motors. It may not happen right away on 1000W but you will stress the dropouts every time you apply power. There is not that much metal there and although you have worked out that the axle won't have optimum leverage on the weakest part, you are tempting fate to not run torque arms.
It really sucks having your motor spin out of the dropouts.
For power levels that are actually fun, forget torque arms: a custom rear arm with huge reinforced slots is necessary.
No. The force is applied from the chain and to the rear cluster. The cluster transfers the force to the hub, spokes and rim. That assembly spins on bearings that ride on the axle. You can't transfer much torque through those bearings considering that the bearings are specifically designed to allow the hub to spin freely. The whole idea is to convert the torque from the chainring to torqe at the rear wheel. It would be counter-productive to be applying that torque to the dropout.
Motor reaction torque is always transferred to the motor mounts. On a mid drive, that's the bottom bracket or some other part of the bike frame. On a hub motor, it's the axle ends.
Axles that are hollowed out for cables on one end can't transmit nearly as much torque through that end as they can through the solid end. So a good thick, tightly fitted, well anchored torque arm on the solid end of the axle is not significantly less secure than having one on each end, though having two is more fault tolerant.