> Seems like more and more companies are moving to mid drives .
It appears that the big players in the bike industry have definitely chosen mids over hubs. Even the major hub builder, Bafang, has developed and is producing a mid-drive.
Mids have the advantage of better gearing which makes them quite efficient. As you likely know, mid systems feed power to the pedal's axle which directs it through the chain to the bike's rear gear cluster. A mid motor unit, itself, contains internal gear reduction which enables the motor to spin happily without much labor. That primary reduction combined with the bike's rear gearing creates a lot of energy for climbing inclines and steep hills. And it can all be accomplished using a small motor which draws less juice from the battery. Less draw means longer range.
> What are some reasons to go with a hub drive ?
Primarily cost, but the savings may not be worth it. To generate the same power to the road surface as a mid-drive, a hub needs to be large, heavy, and watt hungry.
There are two kinds of hubs: geared and gearless.
A gearless design is a motor that uses the wheel’s axle as the armature. To overcome load on inclines, a gearless needs large copper windings and magnets. Not only does that create a lot of weight, but without voltage across the windings the magnets work against the armature to create drag [aka cogging] which a rider needs to pedal against. So, a gearless hub needs to constantly draw battery current.
Geared-hubs are more practical. They have a freewheel-type clutch allowing normal pedaling with the power off. Internally, they have a planetary-gear reduction which lets the motor rotate faster than the wheel to increase the motor's torque output. That gearing also reduces the motor’s labor which is important because load = heat and excessive heat will kill a motor. Unlike a mid-drive, though, which has a secondary transmission back at the derailleur, a hub’s rotational energy goes directly to the tire. That means the hub’s motor is working hard and is prone to heating. To keep heat down with a hub when climbing, the common opinion is not to ride the bike slower than 50% of the hub's rated top speed. Seems simple enough, but with a 20mph hub system that means a 10mph minimum climbing speed. Unless the hub is a large high-watt unit, a rider will have a real workout climbing with a loaded bike, even in granny gear.
