Why is indoor power different from outdoor?

Indoor trainers measure power at different points in the drivetrain compared to outdoor power meters. Wheel-on trainers measure at the rear axle (after drivetrain losses), while crank-based power meters measure before those losses. Temperature also affects trainer resistance and calibration.

How accurate are smart trainers?

Direct-drive smart trainers from major brands (Wahoo, Tacx, Elite) are typically accurate to ±2% after proper calibration. Wheel-on trainers can vary by ±5% or more depending on tyre pressure, roller tension and temperature.

Does temperature affect trainer power readings?

Yes. Wheel-on trainers are most affected because tyre compounds change with temperature, altering the contact patch and rolling resistance. Warm conditions can cause trainers to read 2–5% higher. Always calibrate at your riding temperature.

Should I calibrate before every ride?

Yes, especially for wheel-on trainers. Do a 10-minute warmup, then run the trainer calibration/spindown. This accounts for tyre pressure, temperature and roller tension changes. Smart trainers benefit from regular calibration too.

BikeCalcs

Indoor Trainer Power Correction

Estimate outdoor equivalent power from indoor trainer readings.

Trainer TypeEnter the trainer type

Indicated Power

Power shown on trainer

Room Temperature

Temperature during session

How We Calculate This

Power Correction Model

The correction accounts for three factors:

Trainer accuracy offset: Smart trainers \u00B10%, wheel-on ~5% low, rollers ~8% low
Temperature effect: Warm conditions inflate readings (0.05\u20130.3% per \u00B0C above 20\u00B0C depending on trainer type)
Drivetrain losses: Typically 2\u20134% of power is lost to chain friction before reaching the wheel

Outdoor Equivalent = Indicated Power + Accuracy Offset - Temperature Inflation

Frequently Asked Questions

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Last updated: 2026-03-03

All calculations are estimates. Always verify results and consult a professional bike fitter where appropriate.