If your e-bike stopped showing speed immediately after a rear-wheel or brake-rotor change, check whether the replacement retained the speed-sensor trigger. On systems that use a wheel magnet, that trigger may be attached to a spoke, the rotor, or its lockring. A replacement can fit mechanically yet lack the part the sensor needs. Changing the wheel-size setting will not restore a missing signal.
Compare what came off with what went on
Start with the work that was actually done. Was the complete wheel replaced, just the rotor, or the lockring holding the rotor? Keep the old components or their photographs available until the reading works again.
The sensor arrangement on an electric bike needs to be identified from its actual equipment. Do not assume that every bike has a spoke magnet, or that every metal ring near a wheel is a speed trigger.
Compare the old and new part identifiers with the required replacement parts. A plain lockring and one incorporating a magnet may look similar enough to overlook during a parts order. The useful question for the installer is whether the required trigger was transferred or included, not just whether the new rotor clears the brake.
A pedal sensor near the crank answers a different question: whether you are pedaling. Finding its magnet ring does not confirm that the wheel-speed sensor has what it needs.
Separate a missing signal from an inaccurate number
Describe the symptom precisely. A speed field that stays at zero after the replacement is different from one that continues to change but reads consistently too high or low. The first points you toward the signal path; the second may involve calibration once the hardware is confirmed.
A visible magnet does not finish the check. Its position must suit the sensor, and the sensor wiring may have been disturbed during the work. Those are installation questions, not reasons to glue on another magnet or copy a clearance measurement from a different bike.
Leave the wheel and rotor secured while gathering information. Do not loosen brake hardware, move an unfamiliar sensor, or run the motor with the bike propped up to see what happens. If wheel security or braking is uncertain, do not ride it back to the shop.
Give the installer a specific follow-up
Send the replacement receipt, old and new part identifiers, and clear photos taken with the bike parked and switched off. Include when the reading disappeared and any error shown on the display. Ask for confirmation of the required trigger, sensor alignment, and cable condition.
For the broader work involved, the rear-wheel replacement guide provides the surrounding checks. It does not make an unspecified rotor or lockring interchangeable.
If the correct parts and their installation are confirmed but speed is still absent, let the installer continue the electrical diagnosis. The timing makes the recent work the sensible starting point; it does not prove that the display itself needs replacing.
