E-Bike Conversion Motor Types Compared

Three motor types cover most conversions: front hub, rear hub and mid-drive. The front motor is cheap and simple, the rear motor is balanced, and the mid-drive feels the most natural but is the most work to fit. On top of that there are niche options such as friction rollers and seat-tube motors.

At a glance

Price ranges are rough guides, without guarantee, as of November 2026.

Front hub motor

The front motor sits in the front wheel. You swap the wheel or have yours re-laced, connect cable and battery, and you are done. Gears and coaster brake at the rear stay, and you can combine it with hub gears.

In favour: it is cheap and easy to fit.

Against: the weight sits at the front. On wet roads and gravel the front wheel can spin, and the steering feel changes noticeably.

Not recommended on a carbon fork, on a suspension fork without manufacturer approval, or on very light aluminium forks. With aluminium dropouts you need a torque arm (see torque arm). If you have a front disc brake, the motor needs a disc mount.

Rear hub motor

The rear motor sits in the back wheel. You get good traction and balanced weight distribution. A few things need checking:

• You need derailleur gears. Depending on the motor, a threaded freewheel or a cassette body works, and the number of speeds has to match.
• Hub gears and a coaster brake rule out most rear hub motors.
• The hub spacing has to be right, usually 135 mm (see hub spacing).
• A rear puncture is more work than before.

Mid-drive

The mid-drive sits at the bottom bracket and drives the crank. It uses your gears and feels closest to a factory e-bike, and it is strong on hills (Upway).

The flip side:

• Bottom bracket: Bafang BBS and Tongsheng TSDZ fit shells 68 to 73 mm wide (BSA). Pressfit (BB86/BB92) needs an adapter (fasterbikes). Fat bike shells of 100 or 120 mm usually need their own variants. How to measure is under measure your bottom bracket.
• Coaster brake: The freewheel inside the motor often disables back-pedal braking. Variants with coaster brake exist, see coaster brake.
• Front derailleur: Usually gone. Check chain line and chainstay.
• Wear: Chain and sprockets wear faster. Do not shift under full load.
• Installation: It is complex and not possible on every frame shape (GIGA).

Friction roller

A friction roller presses on the tyre from above or from the side (examples: add-e, Velospeeder). It is light and removable. On the other hand it has little power, it wears the tyre, and it can slip in the wet.

Seat-tube motor

The seat-tube motor (for example Vivax) sits inside the seat tube. It needs a straight seat tube of 31.6 or 30.9 mm diameter (Fahrrad XXL). It is unobtrusive but expensive.

Which motor for which bike?

• Old city bike with coaster brake: Usually only a front hub or a mid-drive with a coaster-brake variant remains. Often a conversion makes little sense here.
• Trekking bike with derailleur: All three standard types are possible. Rear is the good compromise, mid-drive gives the best feel.
• Mountain bike: Mid-drive is the first choice if the bottom bracket fits.
• Road bike or bike with carbon fork: A front motor is out. Rear with 130 mm spacing or a friction roller are more realistic.
• Folding bike: The small wheels (20 inch) are fussy, so check the ETRTO number (see wheel sizes).

Which choice suits you in the end is covered in mid-drive or hub motor.

How reliable is this?

Statements on mid-drive bottom brackets, seat-tube dimensions and the feel of the mid-drive come from the sources named. Price ranges, judgements on front and rear motors, friction rollers and the coaster brake are experience or assumptions that Fabio is still checking.

Does a conversion fit your bike?