PowerTap Pro Cadence



BtonRider

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Jan 30, 2006
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I just purchased the PowerTap a month ago and I've been using the additional Cadence sensor. I noticed it has a built in feature where it analyzes the pulsations in the hub to determine the cadence. Has anyone used the built in feature before? I'm wondering how reliable it is. I wouldn't mind shaving off a few extra grams from the total weight of the PowerTap set up, but only if I can trust the numbers.
 

daveryanwyoming

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Oct 3, 2006
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BtonRider said:
I just purchased the PowerTap a month ago and I've been using the additional Cadence sensor. I noticed it has a built in feature where it analyzes the pulsations in the hub to determine the cadence. Has anyone used the built in feature before? I'm wondering how reliable it is. I wouldn't mind shaving off a few extra grams from the total weight of the PowerTap set up, but only if I can trust the numbers.
When I built up a new road bike last fall I didn't bother mounting the optional PT cadence sensor and have been running it on derived hub cadence ever since. My TT bike and older road bike both use the crank based cadence sensor. The values from both systems seem accurate, hard to know for sure as you measure one or the other at a given time but I don't get cadence drop outs or unrealistic high or low cadence values. Hub based cadence might be a bit jumpier when I look at downloaded files in WKO+ but I use a bit of display averaging and it all seems fine. I guess the related question is how much accuracy do you really need in cadence readings? Will you alter your training or racing if a particular section showed 88 rpm when you really wanted 90 rpm?

-Dave
 

strader

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Jun 28, 2007
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I tried using the calculated cadence and found it very inaccurate. When pedalling at 110+ rpms it would report about half that (~60rpms).
 

BtonRider

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Jan 30, 2006
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daveryanwyoming said:
I guess the related question is how much accuracy do you really need in cadence readings? Will you alter your training or racing if a particular section showed 88 rpm when you really wanted 90 rpm?
True enough. I would just like to be sure it's not off by 20rpm.
 

BtonRider

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Jan 30, 2006
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strader said:
I tried using the calculated cadence and found it very inaccurate. When pedalling at 110+ rpms it would report about half that (~60rpms).
Yikes! Was it more reasonable at lower cadence?
 

flanman

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Mar 13, 2008
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The hub-based cadence works ok, with a few flaws.

It cannot read above about 140 rpm. Don't trust any readings above 120 rpm. This isn't a big issue, but if you're training for track or sprinting then it's better to use the cadence sensor.

rpm for one legged pedalling will be off.

Due, I think, to aliasing, there are some values that it never reads. For instance, it may read 93 or 95 rpm but never 94. There are data holes every 12 rpm or so. This is a minor inconvenience. Set cadence averaging to 3 or 5 seconds and you'll never notice it.

In short, hub cadence sensing is usally good enough for most riders' needs. Be aware of its limitations though.
 

RChung

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Sep 12, 2006
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BtonRider said:
but only if I can trust the numbers.
Depends on what you want to do with the cadence numbers but for most purposes it's a red herring. You have a power meter. Focus on power.
 

strader

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Jun 28, 2007
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BtonRider said:
Yikes! Was it more reasonable at lower cadence?
Yeah, it seemed fine at low cadences. I think for anything higher than ~95 rpm it would read only half the pedal strokes.