A hub motor does not turn on its axle the way an ordinary wheel does. The axle stays still, the motor shell spins around it, and the drive torque pushes back through the axle into your frame. That force is held by a few small parts: stop pins or tabbed washers, plain washers, axle nuts and sometimes a torque arm. Get their order or orientation wrong and the wheel can sit crooked, the nuts can back off, or the axle can start to turn in its slot. Below: what goes where, per Bafang's dealer manuals, and when to add a torque arm.
What usually comes in the box
Most hub-motor conversion kits sold online include the axle nuts and the anti-rotation washers, the ones with a small tab that drops into the dropout slot. They usually leave out the torque arm, so kit buying guides list "is a torque arm supplied?" as a pre-order check.
The order on the axle
Bafang's installation steps differ by model, but the pattern is the same:
- H500 rear fat-bike motor (RM G062): cassette and brake rotor on (six M5×8 screws), stop pin onto the axle, motor into the frame, a 2 mm washer on each side of the frame, flange nuts to 47–60 N·m.
- H550 rear motor (RM G06A2): stop pins and washers on both sides of the axle, M12 flange nuts to 47–55 N·m.
- H560 rear motor (RM G0270): rotor screws 4 N·m, freewheel 35 N·m, a stop pin on each side as the motor enters the frame, bushings on the disc side, then two stages of nuts with different values (47–60 N·m, then 40–45 N·m) using a 19 mm wrench.
- H600 front motor (FM G370): a 0.5 mm washer and the stop pin on the non-cable side before the motor goes in, one 2 mm washer on each side of the frame, cap lock-nuts to 30–36 N·m.
The common thread: the anti-rotation piece engages the dropout slot, plain washers sit against the frame, and the nut goes on last. Installation videos for typical kits describe the loose washers the same way: thin washer first with the tab facing inward so it drops into the slot, the thicker bevelled washer with its bevel facing out, lock nut last. Torque values are model-specific: use your own motor's sheet.
Orientation: the details that cause trouble
- Tab in the slot, on both sides. A tab resting on top of the dropout instead of down in the slot stops nothing, and the axle is not clamped flat.
- Cable pointing down or back. The motor cable leaves the axle on one side only. Rotate the axle so it exits downward or toward the rear before the nuts go on.
- Axle flats that match the slot. Bafang USA's fitment quiz notes its front motors are made for 10 mm fork slots, while some older forks have 3/8-inch (9.53 mm) slots. Measure first; if yours is narrower, have a bike shop check the fork rather than forcing the axle in.
Do not stack washers to make a motor fit
Some motors ship with spacers that let one motor fit two frame widths, but not every motor does. If you add washers or shims, stay within what the manufacturer allows and recheck how much thread the nut is gripping, whether the brake pads are centred, and whether the wheel is centred in the frame. Never stack washers to force a motor into a frame it was not built for. If the width is wrong, measure the dropout width and axle diameter and choose the right motor instead.
When you need a torque arm
A tabbed washer is a small piece of steel pressing on a slot edge; a torque arm adds a longer lever clamped to the frame, so the dropout does not take the whole load alone. When we build a hub-motor parts list, our rule is simple. Fit a torque arm whenever the hub motor is rated 500 W or more, whenever it is a front hub motor, and whenever the dropouts are aluminum. Most kits do not include one, so decide before you ride.
Bafang's H560 manual recommends regularly checking the end nuts on both sides for looseness. If you find a loose axle nut, a wheel sitting off-centre, or a bent or chewed washer tab, stop riding and inspect the dropouts. The motor cable exits through the axle, so any rotation there puts it at risk.
Tools for the job
Hub motor axle nuts are usually 15 mm, sometimes 18 or 19 mm — too big for a folding multitool. A 15 / 18 / 19 mm axle nut wrench set covers those sizes; add a torque wrench so you hit your manual's number instead of guessing. We do not currently stock torque arms, so check your kit or source one separately. If you are replacing the motor, see Motor Wheel vs Bare Hub Motor.
Quick checklist
- Get the installation sheet for your exact motor.
- Anti-rotation piece engaged in the slot on both sides.
- Thin washer first, tab inward; bevel out; nut last.
- Cable exiting downward or toward the rear.
- Nuts at your motor's specified torque.
- Torque arm fitted if the motor is rated 500 W or more, is a front hub motor, or sits in aluminum dropouts.
- Nuts rechecked regularly.
Not sure which motor or dropout you have? See the 4 photos we need to confirm a part fits.