Although manufacturers of bicycle power monitoring devices SRM and Power Tap (PT) claim accuracy to within 2.5%, there are limited scientific data available in support. The purpose of this investigation was to assess the accuracy of SRM and PT under different conditions. : First, 19 SRM were calibrated, raced for 11 months, and retested using a dynamic CALRIG (50-1000 W at 100 rpm). Second, using the same procedure, five PT were repeat tested on alternate days. Third, the most accurate SRM and PT were tested for the influence of cadence (60, 80, 100, 120 rpm), temperature (8 and 21 degrees C) and time (1 h at ~300 W) on accuracy. Finally, the same SRM and PT were downloaded and compared after random cadence and gear surges using the CALRIG and on a training ride. : The mean error scores for SRM and PT factory calibration over a range of 50 - 1000 W were 2.3 +/- 4.9% and -2.5 +/- 0.5%, respectively. A second set of trials provided stable results for 15 calibrated SRM after 11 months (-0.8 +/- 1.7%), and follow-up testing of all PT units confirmed these findings (-2.7 +/- 0.1%). Accuracy for SRM and PT was not largely influenced by time and cadence; however, power output readings were noticeably influenced by temperature (5.2% for SRM and 8.4% for PT). During field trials, SRM average and max power were 4.8% and 7.3% lower, respectively, compared with PT. : When operated according to manufacturers instructions, both SRM and PT offer the coach, athlete, and sport scientist the ability to accurately monitor power output in the lab and the field. Calibration procedures matching performance tests (duration, power, cadence, and temperature) are, however, advised as the error associated with each unit may vary.
And what evidence do you have to back that up? Tests done by Zero Friction Cycling, formerly Friction Facts now owned by CeramicSpeed and others say that it is not “bollox”.
this is a massive can of worms the physics behind how a drive train operates is complex; your total watts in your list is large and can be interpreted differently by each individual that reads it. ceramaic speed are there to sell stuff so naturally they will spin it out to look good for them. general rule of thumb is a well looked after drive train should be 97 -98% effective, so for me with ftp of 250 should be seeing a loss of 5 to 7.5 watts tops; tbh i didnt read your post properly and a lot of those watt losses are duplicates of themselves. I added them all up assuming you meant 30 plus watts loss so apologies for that
I don’t think that zwift should combine the power numbers from the two meters, but rather, allow you to specify one as the primary and one as the secondary “witness” PM for proofing the modulation of the primary.
But this would be really nice if they just incorporated the ability to record from two different sources so it’s all in one place
I’m very close to releasing a Windows app that will capture all relevant ANT+ and BLE sensors, Power, HRM, FEC, MO2, VO2 and data from Sauce4Zwift, and save it all in a FIT file. You can have pretty much as many sensors as you can strap onto yourself or your bike
It remains to be seen what tools we can develop to analyze, for example, multiple power streams. But at least they are all recorded, and no need to merge and match for time. Any FIT tool that can look at Developer Fields will see the additional data fields.
