Most requests for a replacement part arrive with a model name and nothing else. It feels like enough information. It almost never is.
A part fits only when three separate things line up: it has to bolt on, it has to carry the current, and it has to talk to whatever it is plugged into. A model name says very little about any of the three, because bikes are assembled from components that were sourced separately and quietly revised between production runs. Two bikes sold under the same name a year apart can carry different displays, different connectors and different firmware.
Four photographs settle it. Here is what each one is for, and what we read out of it.
The three layers a part has to satisfy
- Mechanical — does it physically go on? Dropout width, axle diameter, wheel size, bottom bracket width.
- Electrical — can it handle the load? Voltage, current, power, phase and hall wiring.
- Communication — can the two ends hold a conversation? Controller and display have to speak the same protocol, and this is the layer that catches people out.
The photos below are simply the fastest way to establish all three from the bike you actually own, rather than from what the bike was called when it was sold.
Photo 1 — the display, straight on
Face on, close enough to read the silkscreen printing on the housing. The model marking is what determines the protocol, and the protocol is what determines whether a replacement will ever work. Two displays that look identical can run different firmware, and a same-model unit from a different batch can be built for a different protocol entirely. Some units expose a parameter setting that switches between protocols; many do not. There is more on reading these markings in our guide to identifying your display model.
Photo 2 — the connector, close enough to count the pins
Then the plug on the end of the display lead, on its own, filling the frame. We are counting three things: how many pins, whether the plug is male or female, and what colour the connector body is. That combination decides whether the new part physically plugs in at all. A display can be exactly the right model and still be unusable because the loom on your bike terminates in a different plug.
Worth knowing: a display lighting up is not proof the link works. The screen can come alive while the speed reading stays dead and the assist levels refuse to change. No error is not the same as talking.
Photo 3 — the controller body and its label
The controller itself, with the specification label readable. Voltage and current rating are the numbers that matter, and they are what we match a replacement against. This is also the photo that answers a question people often ask the wrong way round: display choice has nothing to do with motor wattage. A 500 W bike and a 750 W bike differ in the motor and the controller, not the screen — the same display serves both. If you are still deciding how much to replace, we set out the reasoning in controller, display, or both.
Photo 4 — where the motor cable leaves the axle
Last, the cable coming out of the motor axle, with the conductors visible where they enter the connector. You are counting wires. Eight conductors means three thick phase wires plus five thin hall sensor wires. Nine means the same plus a temperature sensor. That count tells us whether the motor has hall sensors at all, which changes what controller can run it. If the plug is sealed and you cannot see individual wires, photograph the plug face instead and count the holes — the same information, read from the other side, as covered in our look at the nine-pin motor plug.
One measurement to add if a wheel or motor is involved
Photos cannot capture this one, so measure it. With the rear wheel out, measure the clear width between the inner faces of the two frame dropouts. The reading lands on one of three numbers: 135 mm, 170 mm or 190 mm. 170 and 190 do not interchange. Forcing a mismatch springs the frame, leaves the axle poorly clamped, and is genuinely unsafe to ride. Some motors ship with spacers that allow a little adjustment between the two, but not every model does, so confirm it before ordering rather than after. Add the wheel diameter and the tyre width from the sidewall printing while you are there. The full set of measurements is in our guide to hub motor sizing.
Taking photos that are actually readable
Daylight or a torch, not a dim garage. Wipe the label first; road grime hides exactly the characters that matter. Fill the frame with one subject per photo rather than shooting the whole bike and zooming in afterwards — a cropped wide shot rarely holds enough detail to read a pin count. And if the display shows an error code, photograph that too. Code tables differ between models, but the code narrows the search before anyone touches a wire.
Four photos and one measurement, and the guesswork is gone. If your bike takes a matched controller and display together, the paired kit removes the protocol question entirely, because both ends were tested against each other before they shipped.