A ride with my iBike and PowerTap
Posted: Thu Jul 03, 2008 8:08 pm
I have my trusty iBike Gen II on my bike as well as a variety of direct force power meters. Today, the DFPM was my PowerTap.
Earlier this year I used one of the new features of iBike 2 to determine my drag coefficients with and out-and-back ride where the PT is used as the direct-force power reference. This isn't "cheating"; rather, it's a way to have two different measurement devices (the iBike and the PT) be calibrated so that they perform similarly for a given set of ride conditions.
I rode 17 miles today on Montana chip-sealed roads, including the rumble strips on the side of the road. Prior to the ride I let the iBike acclimate to outdoor temperature, then I performed a tilt calibration and wind offset. That was it; the rest was riding.
After my ride I used the iBike 2 software to marry the iBike and PT files together.
I thought you might be interested to see the results. You can download and view the attached file; you'll find that the two devices differed by 0.1W (out of 160) for average power and by 38W out of 780W for maximum power (when I look at the shape of the power burst I find the PT peak data somewhat suspicious).
Also, play around some with the power meter comparison and you'll see that the moment-to-moment data is extremely close.
A lot of this ride was on reasonably flat roads where wind is a major factor. This means that the CdA and Crr measurements were very good. In general I held the same ride position for most of the ride; you should be able to tell from the CdA vs time analysis where I moved around some.
Earlier this year I used one of the new features of iBike 2 to determine my drag coefficients with and out-and-back ride where the PT is used as the direct-force power reference. This isn't "cheating"; rather, it's a way to have two different measurement devices (the iBike and the PT) be calibrated so that they perform similarly for a given set of ride conditions.
I rode 17 miles today on Montana chip-sealed roads, including the rumble strips on the side of the road. Prior to the ride I let the iBike acclimate to outdoor temperature, then I performed a tilt calibration and wind offset. That was it; the rest was riding.
After my ride I used the iBike 2 software to marry the iBike and PT files together.
I thought you might be interested to see the results. You can download and view the attached file; you'll find that the two devices differed by 0.1W (out of 160) for average power and by 38W out of 780W for maximum power (when I look at the shape of the power burst I find the PT peak data somewhat suspicious).
Also, play around some with the power meter comparison and you'll see that the moment-to-moment data is extremely close.
A lot of this ride was on reasonably flat roads where wind is a major factor. This means that the CdA and Crr measurements were very good. In general I held the same ride position for most of the ride; you should be able to tell from the CdA vs time analysis where I moved around some.