Fitting a hub motor conversion kit is one of the most satisfying jobs you can do on a bike: in an afternoon you can turn an ordinary machine into a capable electric one, using little more than the spanners already in your toolbox. Hub kits are popular precisely because they are forgiving. The motor is built into a replacement wheel, so most of the "installation" is really wheel-swapping plus tidy electrical work. That said, a few steps genuinely matter for safety and reliability, and rushing them is how people end up with slipping axles, chewed cables or a motor that refuses to spin. This guide walks through the whole job in order, from checking your bike is suitable to your first power-on test.
Before you start, it helps to understand where this kit sits in the wider picture. If you are still deciding between motor types, read hub motor vs mid-drive conversion kit, and for the broader project context see the complete guide to converting a bike to electric. This article assumes you have already chosen a hub kit and want to fit it properly.
Tools you'll need
You don't need a professional workshop, but gather everything first so you're not hunting for a spanner mid-job. A typical kit install needs:
- A set of metric spanners or an adjustable spanner (axle nuts are commonly 17–19 mm)
- Allen/hex key set and a couple of screwdrivers for the controller bag, display clamp and torque arm bolts
- Tyre levers and a pump to move your tyre and tube onto the new motor wheel
- A torque wrench if you have one, so you can tighten axle nuts and disc bolts to the correct figures
- Cable ties (lots), spiral wrap or self-amalgamating tape for waterproofing, and a sharp knife or side cutters
- A multimeter is handy but not essential for a first-power check
Lay the bike in a work stand if you have one. If not, turning it upside down on grass or cardboard works, though a stand makes wheel removal far easier.
Step 1: Check dropout width and brake type
This is the make-or-break compatibility check, and it takes two minutes. Measure the gap between your dropouts (the slots the axle sits in). A front fork is almost always 100 mm, while a rear triangle is typically 135 mm on older/quick-release bikes or 142 mm on thru-axle frames. Your motor wheel must match. Note that many hub kits use a solid nutted axle, so a thru-axle frame may need an adaptor or simply isn't a good candidate.
Next, confirm your brake type. If you run rim brakes, the motor wheel must have a braking surface and match your rim width. If you run discs, check whether the kit's hub is drilled for the standard 6-bolt or centre-lock rotor, and that your existing rotor will transfer. Sorting this now avoids a frustrating dead-end later.
Step 2: Remove the old wheel
Shift the chain onto the smallest sprocket (for a rear install) to make removal easier. Release the brake if it's a rim brake, undo the axle nuts or quick-release, and lift the wheel out. For a rear wheel, guide the chain off the cassette as you pull the wheel back and down. Keep the axle nuts, washers and any spacers together; you may reuse some of them.
Step 3: Transfer the tyre, tube and rotor/cassette
The new motor wheel arrives bare. Move your tyre and tube across (a good moment to fit a fresh tube and check the rim tape), inflate to your usual pressure, and refit the disc rotor or transfer the cassette/freewheel if it's a rear motor. Take care with rotor bolt torque and check the disc sits true. Doing this before the wheel is in the frame is much easier than wrestling it afterwards.
Step 4: Fit the motor wheel and torque arm
Slot the motor wheel into the dropouts, making sure the axle's flats sit fully home and the motor cable exits cleanly without fouling the frame. Refit washers and nuts finger-tight, centre the wheel, then tighten the axle nuts firmly.
Now the single most important safety step: fit a torque arm, especially on alloy dropouts. A hub motor applies twisting force the dropout was never designed for. Aluminium is soft and can spread or crack, letting the axle spin out under power, which is dangerous. The torque arm grips the axle flats and bolts or clamps to the frame to absorb that twist. Many builders fit one on each side of a powerful rear motor. Do not skip this to save ten minutes.
Step 5: Mount the battery, controller and electronics
With the wheel sorted, work through the electrical components. The exact order is flexible, but a sensible sequence is:
- Battery: mount it on the bottle cage bolts, a rear rack, or in a frame bag. Keep weight low and central for handling, and make sure it's locked or strapped so it can't bounce loose.
- Controller: often it lives in a small bag on the frame or rack. Keep it somewhere ventilated but protected from direct spray.
- Display and throttle: clamp these to the bars where your thumbs fall naturally, without blocking your brake levers or bell.
- PAS sensor: the pedal-assist sensor fits at the bottom bracket, with a magnet disc on the crank axle. This is a cadence sensor on most basic kits, meaning assist comes on whenever the cranks turn. Pricier kits use a torque sensor that responds to how hard you pedal, giving a more natural feel.
- Brake cutoff levers: these tell the controller to kill the motor the instant you brake. Either swap in the supplied levers or fit the small magnetic sensors to your existing ones. Test that braking actually cuts power before any real ride.
Step 6: Connect everything and route cables
Modern kits use colour-coded, keyed plugs, so each cable generally only fits one socket: motor to controller, battery to controller, display, throttle, PAS, and brake cutoffs all click into their matching leads. Plug them together loosely first and check the bike powers up before committing to a final tidy.
Route cables along existing frame lines, following the brake and gear housing so nothing snags on the steering or the moving wheel. Leave a service loop at the bars so the steering has full movement. Bundle the spare cable neatly rather than cutting connectors. Once you're happy, secure everything with cable ties every few centimetres.
For waterproofing, wrap exposed connector joints with self-amalgamating tape or spiral wrap, and make sure connectors point downward where possible so water drains away rather than pooling. Tuck the controller bag's opening away from direct wheel spray. You don't need to make it submersible, just resistant to rain and road grime.
Step 7: First-power checks and troubleshooting
Lift the wheel off the ground, switch on the battery and display, and gently apply the throttle. The wheel should spin freely in the correct direction. Then test pedal assist by turning the cranks, and finally squeeze each brake lever to confirm the motor cuts out immediately.
If nothing happens, work through the obvious culprits: is the battery on and charged, is a brake lever stuck "on" (a very common cause of a dead motor), and are all plugs fully seated? If the wheel spins backwards, some kits have a small wiring reversal plug or a display setting to flip direction. If assist won't engage, recheck the PAS magnet alignment at the bottom bracket. Most "faults" are a loose connector or a brake sensor doing exactly its job.
Safety and final torque
Before the first proper ride, go round every fastener again. Re-check axle nut torque now that the system has been powered, confirm the torque arm is solid, and verify disc bolts and the stem/bar clamps are tight. Spin the wheel and look for rotor rub or a cable touching the tyre. Take a gentle test ride somewhere quiet, building up speed gradually while you get used to how assist arrives.
Finally, remember your kit's manual takes priority over any general guide, and that local rules on motor power and assisted speed apply to you. Check the figures in e-bike conversion laws, watt and speed limits before riding on public roads.
Next steps
Once your hub kit is running smoothly, the natural follow-ups are getting the most from your battery and planning real-world rides. Read the e-bike conversion battery guide to understand capacity, charging and care, and revisit the complete guide to converting a bike to electric if you want a refresher on the bigger picture. After a few hundred kilometres, re-torque the axle nuts and inspect the torque arm, then enjoy the ride.