When power suddenly looks high, low or erratic, the first job is to preserve evidence—not to retest FTP, change zones or declare that the sensor has failed. One ride can be affected by a saved sensor setting, an installation change, a missed right-side connection, a different power source or a genuine change in the rider.
This guide gives you a repeatable order of checks. It uses current manufacturer guidance where products behave differently and avoids universal percentages, battery rules or failure diagnoses that cannot be supported from a ride file.
The first five-minute check
Before another hard effort, record these details:
| Check | What to capture | Why it matters |
|---|---|---|
| Exact power source | Pedal, crank arm, spider or trainer model and sensor ID | A head unit or app may be recording a different nearby sensor |
| Firmware | Meter, head unit, trainer and app versions | Release notes can explain a connection or calibration change |
| Battery or charge | The product's reported state and warning | Low charge can prevent a sensor waking or linking correctly |
| Installation | Recent pedal, crank, chainring, cassette or bike move | Several makers specify calibration or torque checks after installation |
| Configuration | Crank length, single/dual status and selected source | Wrong crank length changes pedal-power calculation; a missing right sensor changes the data available |
| Calibration state | Automatic, prompted or manual result for this model | “Calibrate every ride” is not the correct instruction for every current meter |
Save the original .FIT file and take a screenshot of any error code or calibration value. A manufacturer can use those details; a memory that “the watts felt wrong” is harder to diagnose.
Step 1: confirm which sensor supplied the watts
Indoor setups can broadcast power from the bike meter and trainer at the same time. Dual-sided pedals may also use the left sensor as the connection presented to the head unit while the right communicates through it. Make sure the sensor ID in the head unit or app matches the intended device.
Remove an unintended saved power source or select the desired source in the training app. Do not compare files until you know the same device supplied the number throughout the test.
For a missing right-side Garmin Rally reading, Garmin's official process starts by waking the pedals with several crank revolutions and checking the sensor details. Garmin also says low charge in the right Rally 210 pedal can prevent it connecting to the left. See the Garmin right-sensor troubleshooting page.
Step 2: check installation and configuration
Pedal meters
Confirm the pedal is installed to the manufacturer's torque and orientation instructions. Check the crank-length value in the meter app or head unit. Favero notes that a head-unit crank-length setting can overwrite the app value; Garmin also identifies crank length as a core check when Rally data looks high, low or erratic.
After moving a Favero Assioma to another bike, Favero specifies a manual calibration followed by a few dozen seated, even pedal strokes on flat terrain for internal self-calibration. Use the Favero Assioma FAQ rather than a generic pedal routine.
Crank-arm and spider meters
Confirm crank bolts, chainrings and any installation-specific preload or torque using the component manual. Do not tighten a part simply because a generic article says so. An integrated power meter is also a structural bicycle component; use the correct procedure or a qualified mechanic.
Smart trainers
Confirm axle, cassette or Cog, freehub and bike installation. Then follow the trainer's model-specific calibration and warm-up instructions. Some current direct-drive trainers require no manual calibration, some calibrate automatically and some still specify a spindown in particular circumstances. The current smart-trainer guide links each manufacturer's exact documentation.
Step 3: follow the meter's calibration behaviour
“Zero-offset before every ride” was once common advice. It is not a safe universal instruction in 2026.
Favero Assioma
Favero says current Assioma firmware provides automatic calibration. A manual calibration is required on first installation and when the pedals are installed on a new bike. Favero says daily manual calibration is not necessary. Store the bike upright with no load on the pedals so the automatic process can occur. See Favero's calibration FAQ and PRO installation instructions.
Garmin Rally 110 and 210
Garmin says the current Rally 110/210 pedals calibrate automatically by default while idle. Pedal IQ considers temperature, time since calibration and a changed installation angle, then prompts through a compatible Edge or watch when a manual calibration is needed. When prompted, keep the bike upright and still with nothing touching the pedals and follow the on-screen steps. See Garmin's Pedal IQ guidance.
Do not apply that behaviour to the older Rally 100/200 or Vector generation. Garmin's older-product support can specify a pre-ride static calibration. Product generation matters.
SRAM/Quarq
SRAM describes MagicZero as automatic zero-offset management while riding. Its current manual says power meters released from 2016 onward support MagicZero except DUB-PWR; DUB-PWR uses Manual Zero. MagicZero must be enabled in the SRAM AXS app. See the SRAM MagicZero explanation and Quarq user manual.
For any other brand or generation, open the exact manual. Do not infer behaviour from the word “power meter”.
Step 4: charge or replace the battery as instructed
Battery troubleshooting should be specific and boring. Check the reported charge, warnings, contacts or compartment only where the manual tells you to. Fully charge a rechargeable product or fit the specified replacement cell, then repeat the same test.
Avoid two common overclaims:
- A low battery can prevent a sensor waking or connecting, but that does not prove every low battery creates a predictable high, low or drifting power trace.
- There is no universal “replace every 150–200 hours” rule. Current products use different batteries, battery-life estimates, warning thresholds and charging systems.
If the problem disappears after the supported battery step, record the resolution. If it persists, continue; do not keep changing several variables at once.
Step 5: update firmware deliberately
Read the release notes before updating and keep the previous version in your notes. Firmware can fix auto-zero, missing-sensor, connection or reporting behaviour. Garmin's Rally 110/210 release notes, for example, have included changes to auto-zero behaviour and false missing-right-pedal errors.
An update is not proof that your historical FTP is invalid. After updating, repeat a known steady effort. Change zones only if a stable, repeatable difference affects the source used for testing and training—not because a version number changed.
Step 6: compare a repeatable effort
Use a steady effort that is long enough to avoid sprint timing and smoothing differences. Follow any required trainer warm-up. Record both sources simultaneously if the equipment supports it, then compare the same time window rather than two display snapshots.
Check for three different patterns:
- Stable offset: one device remains consistently above or below the other.
- Changing offset: the gap grows or shrinks during the effort.
- Dropout or spike: one trace loses data or shows an abrupt change not present in the other.
Those patterns help manufacturer support, but they do not identify a failed internal component by themselves.
Why trainer and bike power may differ
A pedal, crank or spider meter and a direct-drive trainer measure at different points. They also have separate tolerances, calibration behaviour, temperature compensation and signal processing. Drivetrain losses can contribute to a difference when comparing upstream and downstream measurement, but they do not produce one universal percentage for every chain, gear, trainer and power meter.
Do not assume that the bike meter must read higher. Do not apply a generic 3%, 5% or 10% correction. Verify the actual pair and pick one consistent source for FTP testing and workout control.
The power meter vs smart trainer guide helps choose the primary source. If the training app supports using a bike meter to control the trainer, check the exact feature and device compatibility before relying on it.
Single-sided estimates can change
A single-sided meter measures one leg and doubles it. If the measured leg contributes a different share because of fatigue, position, injury, cadence or normal variation, the estimated total changes even if true combined output does not move by the same amount.
That does not make the device useless. It means its estimate is not interchangeable with actual dual-sided or spider total power. Test and set zones with one consistent source, and treat an unexpected change as a reason to examine the complete context rather than inventing a “typical” left-right split.
When the rider, not the meter, changed
Power is the external workload, not a complete diagnosis of the athlete. Lower watts at a higher perceived effort can reflect fatigue, heat, illness, fuelling, sleep, pacing or environment. Normal power with an unusually high heart rate or RPE also deserves attention.
Use a repeatable comparison and more than one signal. One familiar climb is not a controlled laboratory test: wind, traffic, surface, position and pacing can all differ.
What to send manufacturer support
If the same issue persists after documented setup, calibration, battery and firmware checks, send:
- exact model, serial number and purchase date;
- firmware and app or head-unit version;
- battery or charge state;
- crank length and installation details;
- the calibration result or error code;
- the original ride file and time stamps of the problem;
- a simultaneous comparison file if one was recorded correctly;
- the steps already completed from the maker's support guide.
Do not open sealed electronics, alter a strain gauge or declare internal failure unless the manufacturer directs the service. A precise evidence package is the fastest route to a warranty or repair decision.
How this guide was checked
Roadman reviewed this page on 25 August 2026 against current Favero Assioma calibration and installation guidance, Garmin Rally 110/210 Pedal IQ and right-sensor support, and SRAM/Quarq MagicZero documentation.
The old version's universal daily-calibration rule, 5–15 W temperature-drift claim, fixed battery schedule, 3–10% trainer offset, guaranteed direction, zero-count thresholds and strain-gauge-failure diagnoses were removed because they were either model-specific, unsupported or too precise for a general guide. Submit a correction with primary documentation through the Roadman corrections page.
Return to training only when the source is stable
Once the issue is resolved, repeat the same check and record the result. Then use the FTP test tool and FTP Zone Calculator from the power source you will actually use.
If you want help turning stable data into a plan, Not Done Yet group coaching combines a personalised TrainingPeaks plan, weekly review, live group coaching, strength and nutrition guidance, and a private rider community.