A problem that looks like a dead hub motor is often something else: a wet or loose motor plug, a Hall signal fault, a brake cut-off holding the motor off, a shorted low-voltage supply, or wires in the wrong order after a controller swap. When the motor really has failed, the replacement comes down to measurements, because a motor that does not match your dropouts, axle and wheel will not go in, however good it is. This page covers both halves: deciding whether it is the motor, then choosing and fitting the replacement.
Is it really the motor?
| Symptom | Check before blaming the motor | Read |
|---|---|---|
| Display on, motor silent, no code | Brake cut-off, throttle and settings come first, then the low-voltage supply the throttle, pedal-assist sensor and Hall sensors share. A short in any of them, including the Hall circuit inside the motor, can pull that supply down, so silence alone does not tell you whether the motor is at fault. | Turns on but won't move |
| Strong but jerky, or rough from a standstill and fine at speed | The Hall signals and the motor plug. | Hall sensor test |
| Judders, stutters or will not spin after a controller or motor swap | Phase and Hall wire order. | 36-combination fix |
| A motor code: 23 or 24 in the shared 21 to 30 family (King-Meter's KM6S manual lists 23 as a motor fault and 24 as a motor Hall signal fault), E65 on the Heybike Ranger 3.0 Pro, E007 on Lectric's XP4 | The motor connector before the motor; the code names a circuit, not a dead part. | Error codes, Heybike E65, Lectric E007 |
| Stopped after rain or a wash | Water or corrosion inside the motor plug. | Inspecting the motor plug |
| Wheel sits off-centre, nuts loose, washer tabs chewed | Stop riding. An axle turning in its slot can tear the motor cable. | Axle washers and torque arms |
| Hall sensors confirmed dead, motor otherwise fine | A controller that can run sensorless may keep the motor in use, though starts from a standstill can be rough. | Sensorless controllers |
Hall sensors sit inside the motor, so reaching them means opening the hub. A confirmed sensor fault leaves three options to weigh on labour, cost and the state of the winding: repairing the sensors, a controller that can run sensorless, or a replacement motor.
If it is the motor: motor wheel or bare hub motor?
A motor wheel arrives with the motor already laced into a rim and trued. You move the tire, tube, brake rotor and freewheel or cassette across, drop it into the frame and connect the cable. A bare hub motor has to be laced into a rim first, which means spokes of the right length, the right pattern, and a wheel tensioned and trued on a stand. For most owners replacing a dead motor, the motor wheel is the safer buy. The bare motor makes sense if you can lace a wheel, have a shop that will, or want to keep your rim. The full comparison is in motor wheel vs bare hub motor, and the swap itself in how to change a hub motor.
Will it fit? Four numbers, and one test
Wheel and tire size are printed on the tire sidewall. The dropout and axle numbers have to be measured, with the wheel out, using a steel rule or calipers.
| Measurement | How | Common values | Watch out |
|---|---|---|---|
| Dropout width | The clear inside gap between the dropouts, in millimetres, wheel removed | Rear: 135 mm on classic mountain-bike style frames, while some road and folding frames use 130 or 120 mm; fat-tire frames use a 170 mm class or a 190 mm class. Front forks: 100 mm is common, fat-tire forks are wider. Measure yours rather than going by type. | 170 and 190 are not interchangeable. Only use spacers the motor's maker allows, and leave any frame spreading to a bike shop. Measuring guide. |
| Axle and slot | Calipers across the axle threads, across the flats where the axle sits in the dropout, and across the dropout slot | Record all three separately; Grin describes 10 mm flats as the standard for slotted dropouts | The slot has to take the axle flats. If it does not, that motor does not drop straight in; have a bike shop judge whether the dropout can be opened up. |
| Wheel diameter | Read it from the tire sidewall | For example 20, 24, 26, 27.5 or 29 inch, or 700c | A motor wheel comes with its rim, so it must match your bike. |
| Tire width | Also on the sidewall, as in 26 x 4.0 | Narrow tires around 1.75 to 2.5 inch; fat tires around 4 inch, on a far wider rim | Diameter alone does not identify a wheel. Quote both numbers. |
The thru-axle test. Take the rear wheel out. If it dropped out of open U-shaped slots, you have open dropouts and the numbers above are the first screen. The freewheel or cassette fitting, the disc rotor position and the brake caliper's clearance to the motor also have to work; Grin's compatibility guide covers these. If you had to unscrew and pull an axle out, leaving two closed round holes, the frame is thru-axle, and a standard bolt-on hub motor will not fit it. A listing that says "fits 135 to 142 mm" is quoting a width, not promising a thru-axle fit. See why a bolt-on hub motor will not fit a thru-axle frame and hub motor sizing. A mid-drive is sized by the bottom bracket shell instead.
Fitting mechanically is half the job. The motor cable's plug and the order of its phase and Hall wires still have to suit your controller, so read the phase and Hall wiring guide before pairing a new motor with an existing controller.
Fitting it: the parts that hold the torque
A hub motor's axle stays still while the shell turns, so drive torque pushes back through the axle into the frame. A few small parts hold that force:
- Get the installation sheet for your exact motor. The washer order and nut torque differ between models; use your motor's numbers, not someone else's.
- Anti-rotation washers engaged in the slot on both sides. A tab resting on top of the dropout instead of down in the slot stops nothing.
- Washers and nut in the order your motor's sheet shows, tightened to its torque with a torque wrench.
- Route the cable as the sheet shows where it leaves the axle, with slack and no sharp bend.
- Decide on a torque arm. Many kits do not include one. Our shop rule of thumb: fit one whenever the motor is rated 500 W or more, whenever it is a front hub motor, and whenever the dropouts are aluminium. It is a guideline, not a sign that a lower-power motor never needs one. Grin Technologies' compatibility guide makes a related point: with a properly fitted torque arm carrying the axle torque, the frame material matters much less.
- Recheck the axle nuts regularly, and stop riding if you find one loose, a wheel off-centre or a bent washer tab.
The step-by-step removal and refit is in how to remove and install a rear hub motor wheel. Moving a freewheel across may need a remover that clears a hub motor's axle and cable, so check the tool against your freewheel and axle before you buy it; see freewheel removal. To support the bike while you work, see how to hold an e-bike safely.
After fitting
- Reconnect the motor cable with the battery out, lining up the arrows or key rather than twisting the plug home. If the new motor's cable has to be joined wire to wire, connect the Hall supply by function, not by colour, and check it with a meter before power-up; a reversed supply can damage the Hall sensors. The 36-combination guide covers the rest.
- Lift the wheel, power up and run it gently: it should turn smoothly in the right direction with no judder. If it judders or runs backwards, stop and find out why before you ride: the wire order, a Hall or wiring fault, or a direction setting.
- Check that each brake lever cuts the motor immediately, then take the first ride at low speed in an open area. See after the install.
Hub motor guides
- How to Test E-Bike Hall Sensors (and When It Means a New Motor)
- Motor Jerks, Stutters, or Won't Spin: The 36-Combination Fix
- Water in the Motor Connector: Inspecting the 9-Pin Plug
- Your E-Bike Motor Runs By Itself: Stop Riding and Read This
- Motor Wheel vs Bare Hub Motor: Which Should You Buy?
- How to Change a Hub Motor: Complete Motor Wheel or Bare Motor
- Hub Motor Sizing: Dropout Width and Axle Diameter Explained
- Thru-Axle Frame? Why a Bolt-On Hub Motor Will Not Fit
- Hub Motor Axle Washers and Torque Arms
- How to Remove and Install a Rear Hub Motor Wheel
- E-Bike Freewheel Removal: Which Tool Fits and What Not to Force
- Sensorless Controllers: A Fix When Your Hall Sensors Fail
When the measurements are written down, compare motors and wheels by dropout width, axle, wheel size and connector. If you are unsure, the four photos we need plus your four numbers settle most fit questions.
Sources
The fit and fault-finding steps follow the RideRow guides linked above. The measurements and code meanings rest on these published sources, which we cite rather than copy; your motor's own installation sheet takes priority, especially for washer order and torque values:
- Grin Technologies, Bike compatibility: 100 mm front and 135 mm rear as the classic spacing most hub motors are built for, narrower road and folding spacings, wider front and 170 to 197 mm rear spacing on fat bikes, 10 mm axle flats in slotted dropouts, thru-axle frames, freewheel and disc-brake fit, and torque arms on aluminium frames.
- Grin Technologies, Hall Sensor Testing (PDF), and Pedego, Dealer Service Guide (PDF, p. 23): Hall supply and signal checks, and isolating a shorted 5 V circuit by unplugging the throttle, pedal-assist sensor and motor one at a time.
- Motor codes 23 and 24: King-Meter KM6S display manual (PDF), which lists 23 as a motor fault and 24 as a motor Hall signal fault; Jasion's EB7 user manual (PDF) labels them as motor and motor-signal issues. Lectric E007: XP4 manual (PDF). Heybike E65: Ranger 3.0 Pro user manual (PDF). More on our error codes page.
What we added: which check comes before blaming the motor, the four measurements in one place, and the order for fitting the parts that hold the torque.
RideRow is an independent parts retailer and is not affiliated with, endorsed by, or sponsored by any brand named on this page. Brand and model names are trademarks of their respective owners and are used here only to identify the bikes and parts each guide covers. This page is general information for owners who do their own work; RideRow sells parts and publishes how-to guides and does not repair bikes. Have a bike shop look at any frame, fork or dropout that is bent or damaged.
Last updated: November 2026