Technically, the PowerTap cannot be user-calibrated, but its accuracy can be checked using a simple test that is similar to the SRM calibration check. First, check that the transmission icon is on, and if not, give the rear wheel a spin. Then, enter the torque mode by holding the “Select” button down for 2 seconds or longer (the “WATTS” designation will disappear from the top line.) Apply the rear brake sufficiently to lock up the rear wheel. Now, measure torque as follows: with the cranks exactly horizontal (right crank at 3 o’clock), hang a known weight of at least 50 lbs from the right crank, or simply stand on it – hence the name ‘stomp test’! Measured torque = (weight in lbs) × (crank length in mm) × (1 in/25.4 mm) × (cog teeth/chainring teeth). For a 159 lb rider standing on a 175 mm crank, with the chain on the 39 tooth ring and the 23 tooth cog, 159 lbs × 175 mm × 1 in/25.4 mm × 23/39 = 646 in-lbs. Compare this to the displayed value by calculating % error as (measured torque - displayed torque)/measured torque.
when i enter rides manually from bikes with no power measuring capability, the Power Dist and HR Dist charts for last 28 days have outlandish spikes in them which ruins the charts
anybody else dealt with this?
google the details.
PowerTap has been flaky the last couple of rides (reading ~40 watts too low across ranges and downloading nonsensical data). I asked around and finally called Saris. Their advice:
i played around some more with manual entries and I'm not happy with the results; as soon as you put in an intensity factor then a constant average power is calculated and then there is a spike in the power distribution chart; if if is omitted then the tss and if chart shows a day with 0 IF which is obviously wrong
i'm not seeing a smooth way to integrate information for efforts that are estimated; maybe i'm missing something or maybe i'll learn more about what matters with more experience
Today I shattered pretty much all of my power records for durations over 5 minutes.
Full post here in the training status thread:
Yes, I'm psyched!
Last edited by ridethecliche; 04-27-09 at 11:02 PM.
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next question is on power profile testing, 5 sec, 1 minute, 5 minute....
is it good to test on slightly inclined road? without the incline I find myself running into bike handling challenges (turns, dips, bumps, gravel) and downhills (lots of rollers here the NC Piedmont)