Symptoms
- Motor kicks in a second or two after you start pedaling
- Assist power surges suddenly rather than smoothly
- Assist cuts off abruptly when you stop pedaling
- Feels different in different assist modes
Likely causes
- CommonNormal lag from cadence-based sensorsCadence sensors detect pedal rotation and inherently have a slight delay compared to torque sensors, which is normal for that sensor type.
- CommonDirty or misaligned sensor magnetsThe magnet ring near the crank needs to be clean and properly spaced from the sensor to work smoothly.
- PossibleLow battery affecting power deliveryPower delivery can feel less smooth as the battery gets very low.
- PossibleSoftware or firmware needing an updateSome manufacturers release firmware updates that improve assist smoothness.
What to do
- Confirm what type of sensor your bike uses (cadence or torque) in the manual, since cadence sensors have inherent, normal delay compared to torque sensors.
- Clean the magnet ring and sensor near the crank of any dirt or debris.
- Check the sensor sits at the correct distance from the magnets per the manual, usually a few millimeters.
- Try a full charge and test assist smoothness again, since a low battery can affect power delivery.
- Check the manufacturer's app or website for any available firmware updates for your motor system.
- Test different assist levels to see if the issue is consistent across all of them or specific to one.
- If jerky assist persists after cleaning and isn't explained by normal cadence-sensor lag, an e-bike shop can test the sensor and controller.
Tools and parts
- Small screwdriver
- Cleaning cloth
Cadence sensorSearch: “e-bike cadence sensor replacement”
When to call a pro
An e-bike shop can test the sensor and controller, and check for available firmware updates that improve assist feel.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.