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Power Tap Power Number is Jumpy

Old 05-18-07, 03:12 PM
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Power Tap Power Number is Jumpy

So I now have about 15 hours on my PT. One thing I have noticed is the power reading while I am riding fluctuates a lot. I am talking as much as 40-80 watts every second or two. Is that normal?
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Old 05-18-07, 03:13 PM
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Depending on the terrain/conditions, power can fluctuate quite a bit. When was the last time you zeroed the torque?
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Old 05-18-07, 03:57 PM
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I zeroed it out when I first got it...15 hours of ride time ago. It shows 0 when I coast.
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Old 05-18-07, 04:00 PM
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Probably it is set for 1-sec averaging, which is very jumpy. You can use the PowerAgent software to set it to 5 or 10 second averaging instead. Check your manual for how to do it in setup mode on the device itself. Note that this only affects the *display* on the device. The measurement and recording are unaffected.
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Old 05-18-07, 04:00 PM
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It's normal. Nobody's power is super even. That's why there's almost always a smoothing factor applied when you view the data.

You'll get used to it quickly. You'll also learn to pedal more smoothly.
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Old 05-18-07, 04:07 PM
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2 sec averaging. also zero your torque before every ride.
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Old 05-18-07, 04:24 PM
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Playing with the Averaging only matters if you're in AV WATTS mode. At any moment, your power can and will fluctuate quite a bit, especially if you have an uneven pedal stroke. One of the nice things is that you can use that to learn a smoother pedal stroke.

Another thing that's mentioned with Powertaps is something called "progression," which apparently causes the power to fluctuate the further your cadence is from 95 rpm, IIRC. That's just a function of the power meter.
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Old 05-18-07, 05:58 PM
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Maybe you can take a screen capture to show us what you mean.

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Old 05-18-07, 06:26 PM
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Originally Posted by DrPete
Playing with the Averaging only matters if you're in AV WATTS mode. At any moment, your power can and will fluctuate quite a bit, especially if you have an uneven pedal stroke. One of the nice things is that you can use that to learn a smoother pedal stroke.

Another thing that's mentioned with Powertaps is something called "progression," which apparently causes the power to fluctuate the further your cadence is from 95 rpm, IIRC. That's just a function of the power meter.
No, the reported "current power" also has an adjustable smoothing factor. I'm going to increase mine now.
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Old 05-18-07, 06:33 PM
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Originally Posted by recursive
No, the reported "current power" also has an adjustable smoothing factor. I'm going to increase mine now.
It may affect AV WATTS mode as well, but the setting definitely affects current power. I originally had mine set at 1 or whatever the default is, and switched to 10. There is a very noticeable difference in plain WATTS mode, not AV. Most noticeably, when I stop pedaling I can watch the WATTS slowly wind down to zero. How long? About....10 seconds...
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Old 05-18-07, 07:05 PM
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Incidentally, the documentation is pretty clear that the smoothing factor does not modify the sampled data but only what is displayed on the CPU. When you upload it to the CP software the smoothing level of the CPU has no effect whatsoever.

Obviously, this is a bit tangential to the OP, but I thought I'd mention it.

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