Hub Motors and Mid-Drives Do Genuinely Different Jobs

Both approaches to electric motor placement work. What differs is what they cost you, and the cost is what this sets out.

Where the motor sits and what it drives

A hub motor is built into the front or rear wheel and drives that wheel directly, independent of the chain and gears. A mid-drive sits at the bottom bracket and applies its power to the chainring, so its output passes through whatever gear you have selected. That distinction is the whole story, because it decides whether the motor can be kept in an efficient speed range on a climb.

A hub motor on a steep hill is forced to turn slowly regardless of your gear, which is where it draws high current and gets hot. A mid-drive in a low gear keeps spinning at a comfortable rate while the bike moves slowly, which is exactly what a motor prefers.

Climbing and heat

Electric motors are most efficient within a band of rotational speed, and they lose efficiency sharply when forced to turn slowly under high load. The energy that does not become motion becomes heat, and sustained heat is what damages motor windings and controllers. Hub motors on long steep climbs are therefore working at their least favourable point exactly when you need them most.

Geared hub motors, which contain internal reduction gearing, handle this better than direct-drive hubs but still cannot use the bike's gears. For flat and gently rolling routes the difference is small, and for a genuinely hilly commute it is the deciding factor.

What each does to the rest of the bike

A mid-drive sends motor torque through the chain, chainring and sprockets, so those parts wear noticeably faster than on a normal bicycle. Riders of mid-drive bikes replace chains more often and should ease off pedal pressure while shifting, since shifting under motor load damages sprockets.

In the saddle, a hub motor leaves the drivetrain carrying only your own effort, so chain wear is close to that of an unpowered bike. Hub motors add unsprung weight at the wheel, which affects handling slightly and makes the wheel heavier to lift or carry. They also complicate puncture repair, because the wheel carries a motor cable that must be disconnected or worked around.

Weight distribution and handling

A mid-drive concentrates its mass low and centrally, which is the best place on a bicycle for heavy things to live. A rear hub motor puts weight behind and low, which is acceptable but adds to the load already on the rear wheel.

A front hub motor puts weight ahead of the steering axis, which can make the steering feel heavy and reduces front wheel traction on loose surfaces. Front hub motors also apply drive to the wheel that steers, and on wet or gravelly surfaces that can produce a wheelspin most riders find unsettling.

For a bike carrying luggage or a child seat, the central mass of a mid-drive is a real advantage.

Cost, repair and conversion

Hub motor systems are generally cheaper, both to buy and to replace, and conversion kits for ordinary bicycles are almost all hub-based. Their simplicity is genuine, since a hub motor is a sealed unit with few serviceable parts and no interaction with the transmission.

Mid-drive systems are more expensive, more integrated into the frame, and usually tied to one manufacturer's parts and diagnostics. That integration means a fault often needs a dealer with the right software rather than any competent bike shop. Weigh that against the fact that mid-drives generally last well when the drivetrain is maintained.

Frames, sizes and riding positions vary enormously; borrow before you buy wherever you can.

Choosing one for your route

Flat city, short distances, modest budget and a bike you may want to convert yourself all point clearly towards a hub motor. Steep hills, heavy loads, long daily distances and a preference for a bike that rides like a bicycle point towards a mid-drive. Test ride both on the steepest hill you routinely climb, because a showroom car park tells you nothing about the difference.

With a loaded rack, ask specifically what happens to warranty and servicing if the motor fails, since that answer varies enormously between systems. Neither is better in general, and any shop that says otherwise is describing its stock rather than your route.

Side by side

The takeaway

If your route has hills, buy the motor that can use your gears; if it does not, save the money.

Fix the small rattle. Every large repair began as one.