My Power Meter Output Is Different From My Smart Trainer

You can expect a difference in the power measurement when comparing a power meter to a smart trainer's power value. This is a normal result of power being measured from different locations on a bike.

How Does This Happen?

With pedal-based power meters, the power is transferred directly from the rider's foot to the point of measurement in the pedal. Crank-based power meters may experience a discrepancy due to power transfer between pedals and the crank arm. On a smart trainer, the power travels through the crank arms and chain before it reaches the point of measurement in the smart trainer. A percentage of power will always be lost through a chain. Bike chains cause a loss of up to 5% in power when comparing power levels between a power meter and a smart trainer with power measurement.

To keep this variance to a minimum, make sure of the following:

• Vector/Rally pedals need to be torqued down to spec (25-30 ft/lbs).

• Calibrate Vector/Rally pedals using a head unit such as a Garmin Edge or compatible Garmin watch before each ride.

• If using a 3rd party power meter, calibrate using the manufacturer's specified method.

• Calibrate the smart trainer if possible. This is typically done using an app provided by the smart trainer manufacturer.

• Use a new and clean chain as a worn or dirty drivetrain will produce less accuracy and more noise.

• Make sure both the smart trainer and power meter pedals are running current software.

NOTE: You will never see a power difference of 0% between power meter pedals and smart trainers. Although replacing a chain and cassette will minimize the difference, it will never eliminate it.