Symptoms
- Power numbers seem way off from perceived effort
- Readings jump around erratically
- Power reads zero even while pedaling hard
- Numbers drift over the course of a long ride
Likely causes
- CommonTrainer needs a spin-down calibrationMost smart trainers require periodic calibration through the app to stay accurate as tire pressure and temperature change (or directly for direct-drive units).
- CommonTire not seated or pressure wrong (wheel-on trainers)Incorrect tire pressure or slippage against the roller throws off power estimates on wheel-on trainers.
- PossibleTrainer hasn't warmed upSome trainers read inaccurately for the first several minutes until internal components reach operating temperature.
- PossibleOutdated firmwarePower curve accuracy improvements are often released as firmware updates.
- Less commonFailing power sensor or strain gaugeOn direct-drive trainers, the internal sensor can degrade or fail.
What to do
- Run the manufacturer's calibration or spin-down procedure through their app before every ride if recommended.
- For wheel-on trainers, confirm tire pressure matches the manufacturer's recommendation and the tire is pressed firmly against the roller.
- Let the trainer warm up for 10 minutes with light pedaling before relying on power numbers for a hard workout.
- Check for and install any firmware updates through the trainer's companion app.
- Compare readings across two different apps if possible to see if the issue is the trainer or one specific app.
- If numbers stay implausible after calibration and firmware updates, contact the manufacturer, since the internal sensor may be degrading.
When to call a pro
Contact the manufacturer's support if calibration and firmware updates don't fix inaccurate readings, since the internal power sensor may need repair.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.