Comparison Between the SRM and PowerTap Power Meters to the iBike Pro Power Meter




Dix, Ross A.

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The purpose of this study was to compare the Schoberer Rad Messtechnik (SRM) and PowerTap bicycle-mounted power meters to the new iBike pro bicycle-mounted power meter, in order to determine whether the iBike pro, which measures power using wind speed, hill gradient, and the weight of the cyclist and their bike, measures power output as accurately as the SRM and PowerTap power meters, both of which measure power based on torque. Seven competitive cyclists and one competitive triathlete preformed three experimental trials. The three trials consisted of three different experimental conditions: a radical hill climb and descent, a rolling training ride, and a flat time trial ( during which sprint data were collected). The trials were preformed on the same day with a recovery period between. The SRM and PowerTap were extremely highly correlated during the hill climb, time trial, and sprint interval with correlations of 0.99 for each of the trials. The iBike was extremely highly correlated with both the SRM and PowerTap during the hill climb trials with correlations of 0.99 and 0.98 respectively. There was a significant mean difference between the SRM and both PowerTap and iBike during all of the trials; F(2,14)=38.26, p=.000002 (hill climb), F(2,14)=17.00, p=.00018 (training ride), F(2,14)=32.49, p=.000005 (time trial), F(2,14)=22.32, p=.00004 (sprint interval), and F(2,14)=14.47, p=.0001 (all trials). There was not a significant mean difference between the PowerTap and iBike during the hill climb t(7)=0.58, p=.29, training ride t(7)=0.61, p=.28, and sprint intervals t(7)=1.65, p=.07, but was a significant mean difference during the time trial and all trials combined. In conclusion, the iBike may be less consistent when compared to the SRM and PowerTap because of the large number of variables that are used by the iBike to calculate power. However, based on the high correlation between the iBike and both the SRM and PowerTap, it is likely that the iBike could be used for a power based training program. Nevertheless, coaches and exercise scientists should be cautioned about using the iBike or any power meter to determine very small changes in power output.



bicycles, power mechanics, design and construction, cyclists, training, equipment and supplies


Dix, R. A. (2008). Comparison between the SRM and PowerTap power meters to the iBike pro power meter (Unpublished thesis). Texas State University-San Marcos, San Marcos, Texas.


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