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Old 11-04-12, 11:48
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Originally Posted by Alex Simmons/RST View Post
I'm not so sure. I think it'll have potential to be another gateway drug, but not a killer app.

It only measures the left leg and doubles that to report total power output, which relies on the invalid assumption that power production is left-right symmetrical, when in fact L-R asymmetry is normal, and not only is asymmetry normal, the level of asymmetry is not consistent person to person, nor is it consistent for the same person (it varies depending on absolute and relative power output, cadence, fatigue level, type of riding, bike and so on).
Some good points AS.

I'm still not sure you say you can't calibrate the PT when Garmin say you can in that link I provided before.
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Old 11-04-12, 11:55
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Despite measuring on one side (left), the unit does correctly give you total power by taking the left power and applying an algorithm to determine total power. If you compare it to spider based power meters, that is measured at the spider, which takes into account force from both cranks.

Note however that none of the left/right crank based power meters currently available on the market today however independently measure left/right power. They all estimate it. The only direct force power meter today on the market that separately measures left/right power is the Polar/Look pedal based power meter. There are crank based units coming down the line next year that will measure it independently (i.e. the ROTOR system).
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Old 11-04-12, 21:25
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Some good points AS.

I'm still not sure you say you can't calibrate the PT when Garmin say you can in that link I provided before.
Just because Garmin misuse the word calibration, does not make it so.

Calibration of any measuring instrument is a process of ensuring that the device is reading accurately. That involves both checking it and making the necessary adjustments to ensure the data is accurate.

You can do the first bit with a Powertap, but not the second.


It's like a set of bathroom scales. It gives you the ability to check the zero point is set correctly by reading zero kg when you are not standing on the scales. But what if you then place a precisely known 50kg mass on the scales and they read 48kg? There's nothing you can do to fix the bathroom scales that will make them accurately report weight.
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Old 11-04-12, 21:40
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Despite measuring on one side (left), the unit does correctly give you total power by taking the left power and applying an algorithm to determine total power.
All its "algorithm" does is double the left leg reading, which falsely assumes that our power output is always symmetrical, and under all circumstances.

This is not the case. Asymmetry is normal and it varies significantly.

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Originally Posted by durianrider View Post
Note however that none of the left/right crank based power meters currently available on the market today however independently measure left/right power. They all estimate it. The only direct force power meter today on the market that separately measures left/right power is the Polar/Look pedal based power meter. There are crank based units coming down the line next year that will measure it independently (i.e. the ROTOR system).
Sure, but that's a red herring and does not speak to the invalid assumption being made by StageOne.

And besides, even the StageOne can't tell you left leg data independently, since the cranks are connected it's telling you the net forces on the left crank applied by the whole system (i.e. both legs).


As for knowing left-right power, to be frank, it's way over rated as an issue to be concerned with in any case, but that's an entirely different discussion.
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