Hi there, I just wanted to ask the brains of the forum a question about the difference between SRM and PT. I have a PT pro and have used it for 2 years. I recently purchased a second hand Dura Ace SRM, wired. I expected there to be a difference in the powers with the PT being on the low end due to the loss in the drivetrain but was surprised to find that it was a difference in the opposite direction. I knew that the slope was not to be trusted and calibrated the SRM but there is still about a 20W difference at 100W for the PT and 80 for the SRM. I also checked the accuracy of the PT through a the torque readings only to find that it was pretty accurate. Any advice or ideas of what the problem could be and how to fix it? Thanks
Power meters · Public discussion
SRM vs PT power difference
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- Power meters
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- 16 April 2010
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- 21 April 2010
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- jannesbwessels
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Did you calibrate the slope on the SRM yet? If not, there's some good directions here.
Compared to a wired powertap I was using, my SRM is about 5-10watts lower at 200w, I just had to change my FTP slightly in Wko+ to compensate. -
20 watts is a lot to attribute to a drive train - unless yours is particularly messy 😉
IIRC, 7-10 watts is about right and is fairly constant across power outputs.
You didn't say how you calibrated your SRM. The directions sited by mx416 are pretty good and what I've been using. There's also a spreadsheet in the files section of the "Wattage" group on Google that's pretty handy for calibrations.
Dave
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dkrenik said:
20 watts is a lot to attribute to a drive train - unless yours is particularly messy 😉
IIRC, 7-10 watts is about right and is fairly constant across power outputs.
Dave
Not only is 20W a large number, but his PT is reporting HIGHER power than his SRM.
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jannesbwessels said:
Any advice or ideas of what the problem could be and how to fix it? Thanks
How did you check calibration of each?
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