Taking out a rear wheel with a hub motor in it is not hard, but it has more parts in play than an ordinary wheel: a motor cable that leaves through the axle, flat-sided axle ends that must sit square in the frame, shaped washers, sometimes a torque arm, and large nuts with a specified torque. Get those right and the wheel goes back exactly as it came out. Get them wrong and the axle can turn in the frame, which can tear the motor cable.
What you need
- An axle wrench in the right size. Hub motor nuts are commonly 15, 18 or 19 mm; check yours before you start.
- A torque wrench that reaches your axle nut torque, with a crowfoot or socket that fits around the motor cable.
- Hex keys for the torque arm bolt, side cutters for cable ties, new cable ties and a little grease.
- Your phone, for photos.
Removing the wheel
- Turn the bike off and remove the battery. Unplug the charger too. Rad Power Bikes also has owners press the MODE or power button on the display once the battery is out, to drain any power left in the system.
- Shift to the smallest rear sprocket. This gives the chain the most slack and makes the wheel easier to drop out.
- Support the bike on a stand clamped on the seatpost, or upside down on a soft mat; see how to hold an e-bike safely for repair.
- Photograph both ends of the axle. Record the order and direction of every washer, the torque arm, any derailleur hanger and the kickstand plate. This photo is your reassembly guide.
- Unplug the motor cable at its connector, usually along the chainstay. Cut any cable ties holding it, then pull the two halves straight apart. Do not twist the connector.
- Deal with the brake. With disc brakes, leave the caliper in place and do not squeeze the lever while the wheel is out. With rim brakes, open the brake release.
- Remove the torque arm bolt, if your bike has a torque arm.
- Loosen both axle nuts a few turns, but leave the nuts and washers on the axle. Rad's guide points out that the orientation of the torque arm and torque washers matters for safety, so keep them in order.
- Drop the wheel out. Pull the derailleur body back, lift the bike and let the wheel come down out of the frame, easing the chain off the sprocket.
Installing the wheel
- Clean the frame slots (the dropouts) and the axle. A thin film of grease on the axle threads helps the nuts tighten evenly. Keep grease off the flat faces that sit in the slots.
- Set the chain and guide the axle in. Put the chain on the smallest sprocket and slide the axle all the way into both dropouts. The flat sides of the axle must sit fully inside the slots, because they are what stops the axle from turning.
- Refit the washers and torque arm exactly as your photo shows, with any washer tabs dropped into the slot rather than resting on top. If one end of the axle is solid and the other has the cable coming out, Grin's torque arm manual says the arm belongs on the solid side, where the axle is stronger.
- Centre the wheel and make sure the brake rotor sits between the pads.
- Tighten the axle nuts to the torque in your bike or motor manual. As examples, Rad Power Bikes specifies 40 N·m for its rear hub motor axle nuts, and Grin asks for at least 60 N·m on an axle fitted with its V5 torque arm. Values differ between motors, which is why the manual matters. Never ride, and never touch the throttle, with nuts that are only hand-tight: Grin notes that this is a classic way to spread the dropouts and spin the axle after a flat repair.
- Tighten the torque arm bolt to its own value, which is much lower than the axle nuts. Rad lists 2 to 5 N·m depending on the model, and Grin lists 6 to 8 N·m for the screws on its V5 arm.
- Reconnect the motor cable, lining up the arrows or keys and pushing it fully home. Leave a gentle loop near the axle so the cable is not pulled tight, and tie it to the frame away from the spokes, disc and derailleur.
- Check before riding. Spin the wheel to see it runs straight and clear of the brake, squeeze the brake lever several times, shift through the gears, then refit the battery and test the motor with the wheel lifted off the ground before a slow test ride. Our after-the-install checklist covers the power-on checks.
When you need a torque arm
A hub motor pushes back on its axle every time it drives the wheel, and the frame slots alone have to hold that force unless something else helps. Our rule for RideRow repair plans: 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. Above 1000 W, or on any motor with regenerative braking, treat it as essential rather than optional. This follows Grin Technologies' guidance, which recommends a torque arm on installations over 500 W or on aluminum forks and says it should be used for sure on powerful, front aluminum or regen setups.
For the order of washers and how a torque arm sits on the axle, see our guide to hub motor axle washers and torque arms.
Warning signs
- A wheel that sits crooked, a nut that keeps loosening, or a washer tab that is bent or chewed: stop riding and inspect the dropouts.
- A motor cable that is kinked or cut where it leaves the axle usually means the axle has turned. Do not power the bike until it is checked.
- Never run the motor with the cable only partly plugged in, and never lift the bike by the motor cable.
If the wheel will not fit your frame at all, measure it with our dropout width guide, and check whether your frame uses a thru-axle.