2009 SRM - Power Data Lower than Power Tap

onebadjd said:

I have been training with Power Tap and Ergomo power meters for the past few years. The power of each meter was consistent. I recently decided to upgrade and purchased an FSA SRM with a power control VI. My power output with the SRM is consistently 12-18% lower than what is shown on my power tap and what a similar ride would have produced using an erogomo. While training today a friend had an SRM with a p.c. V. As we rode along the flats, I noticed his display significantly higher than mine so we switched bikes. I understand that a persons weight etc. will have an impact on the power numbers, but once I got on his bike and he on mine, my numbers were higher. I have double checked to make sure the proper slope is inputed. Has anyone else experienced this problem? If so what causes it and what is the fix. Thanx.

Perform a calibration check on the SRM slope.
Often factory slopes are wrong. Not usually by that much though.

Check the SRM zero offset is set properly before riding.

Alex Simmons said:

Perform a calibration check on the SRM slope.
Often factory slopes are wrong. Not usually by that much though.

Check the SRM zero offset is set properly before riding.

Thanx Alex, I zero offset before each ride. I am not sure how to perfrom a calibration check. I downloaded the manual from SRM so I'll check on how to perform the calibration.