Your FTP Might Be Fake
If your power meter isn’t regularly calibrated (strictly speaking, “zeroed”), the wattage you see during training could be off by 5-10%. That means the FTP you think is 250W might actually be only 225W—or conversely, you might be stronger than you think.
Calibration vs. Zero Offset: Concepts Cyclists Often Confuse
| Term | Who Does It | How Often |
|---|---|---|
| Calibration | Factory | Once at the factory |
| Zero Offset | Yourself | Before every ride |
Calibration is establishing the “force input → value output” relationship at the factory using precision equipment. You can’t do this yourself.
Zero Offset is telling the power meter, “No force is being applied to me right now, and this is zero.” You need to do this frequently.
Why Do You Need to Zero?
The strain gauge in your power meter is affected by temperature. If you prep your bike in an air-conditioned room and then ride out into Taiwan’s 35-degree blazing sun, the temperature difference can cause reading drift.
Zeroing eliminates this drift.
Zero Offset Steps (General)
- Rotate the crank to a vertical position (12 o’clock and 6 o’clock)
- Make sure there is no weight on the pedals
- Activate the “Calibration” function on your bike computer
- Wait a few seconds for it to complete
- Note the zero offset value (usually around 890 ± 50, depending on the brand)
When to Zero?
| Timing | Importance |
|---|---|
| Before every ride | ★★★★★ |
| After replacing drivetrain components | ★★★★★ |
| After drastic temperature changes | ★★★★ |
| Every 30 hours of riding | ★★★★ (minimum requirement) |
| Before a race | ★★★★★ |
Daily Power Meter Maintenance
| Item | Frequency |
|---|---|
| Zero offset | Before every ride |
| Battery/charging | Replace/charge when low |
| Firmware updates | When a new version is available |
| Cleaning | Monthly (don’t use high-pressure water) |
| Bolt torque check | Monthly (for crank-based power meters) |
Notes for Different Types of Power Meters
| Type | Maintenance Tips |
|---|---|
| Crank-based (e.g., Stages, 4iiii) | Pay attention to the battery cover waterproof O-ring |
| Spider-based (e.g., Quarq, Power2Max) | Regularly check chainring bolt torque |
| Pedal-based (e.g., Garmin Rally, Favero Assioma) | Clean pedal bearings, watch for cleat wear |
| Hub-based (e.g., PowerTap) | Check the power sensor during hub maintenance |
Battery Management
- Low battery causes inaccurate readings—don’t wait until it’s completely dead to replace it
- CR2032 coin batteries (used by some brands) last approximately 200-300 hours
- For rechargeable power meters that have been idle for a long time, fully charge them before use
Accuracy Verification
If you suspect your power meter is inaccurate, you can:
- Cross-check with another power meter (e.g., pedal-based vs. crank-based)
- Perform a known test (e.g., riding a fixed power on a trainer)
- Send it back to the factory for recalibration
The power meter is the core tool of your training. Ensuring its readings are accurate is what makes your training meaningful.
Related Reading
- Power Meter Selection and Calibration: Differences Between Static and Dynamic Calibration and Frequency Recommendations
- Power Meter Buying and Calibration: The Impact of Accuracy Error on Training Data
- Common Power Training Mistakes: Excessive Intensity, Insufficient Recovery, and Inaccurate FTP Testing
- 2025 Complete Power Meter Buying Guide: Best Choices from Entry-Level to Advanced
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