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PostPosted: Mon Sep 21, 2009 10:08 pm 
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The Stig wrote:

I prefer power at the wheel is because I'm coming from an auto perspective, which I think is more "realistic" (excuse the term "accurate"). I think it would be fair to say that someone putting 300 watts of power at the wheel is a bit stronger than someone putting 300 watts at the pedal, wouldn't you say? I'm not taking into account other factors because that's another story. As for your last statement, the hub is the closest thing you could get to net power, unless you want to put the bike on a dyno and account for tire losses, etc... Like I said Jason, it's just me. :beerchug: Just prefer a bigger picture that's all....


Your choice of the word accuracy is subjective. If the purpose of you data is to train, than you want accurate readings from the rider, not the whole picture as you state it. If there are differences in drive-train efficiency you would have to know those differences in order to get accurate data for the rider. In your logic you would have to have both power readings from the crank/pedal and the hub/tire so you can determine if there is a loss in power due to rider issues (fatigue, nutrition) and not bike issues. Without crank/pedal data you have no way of knowing this and therefore are being less accurate for the purpose at hand.

You can prefer it all you want, but the point of a power meter is to develop the rider and the most accurate way to do that is to measure that data as close to the rider input as possible. You don't want variables from the bike to confuse the issue when each watt counts.

-Eric

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PostPosted: Tue Sep 22, 2009 12:57 am 
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This is sort of a silly debate, over 1-2% difference in drivetrain efficiencies on units which have only 1-2% precision....

But there is a side advantage to my powertap. Since I get competitive with myself on power, it causes me to pay more attention to my drivetrain, since I want to maximize my power. This is a good thing. As Kraig Willett says, "fast is fast". A pragmatic crutch, sure, but like the crutch of setting my watch precisely 90 seconds fast to help me be on time, it works.

In contrast, I tend to get sloppy on my tire pressure, since I know PowerTap has that under control. Were I to use an iBike, I'd pay more attention to tire pressure, as well.

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Posted: Tue Sep 22, 2009 12:57 am 


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PostPosted: Tue Sep 22, 2009 1:03 am 
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djconnel wrote:
This is sort of a silly debate, over 1-2% difference in drivetrain efficiencies on units which have only 1-2% precision....



True.

I just thought the argument of taking into account the drive-train as the whole picture doesn't wash if one is using this devise for it's intended purpose, to train the rider.

-Eric

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PostPosted: Tue Sep 22, 2009 1:10 am 
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There's only one way to solve this! Mount the new Metrigear pedals onto an old SRM that fits a Ergomo BB. Then have a PowerTap rear hub and to top it off the Polar power meter. Then measure all the data up against each other and see which one comes out most accurate! :twisted:

No matter spending those thousands on power measuring equipment! Personally, I've never needed nor wanted a power meter. I've had ample power at my disposal.

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PostPosted: Tue Sep 22, 2009 1:20 am 
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AWESOME!

You can do better, though.... add this puppy to the stew:

http://www.google.com/patents/about?id= ... q=11936847

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PostPosted: Tue Sep 22, 2009 2:11 am 
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What's next? Power meters build into socks? :shock:

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PostPosted: Tue Sep 22, 2009 2:29 am 
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HOLD THAT THOUGHT.

I know a good patent attorney....

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PostPosted: Tue Sep 22, 2009 2:53 am 
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Great idea, but strain gauges are dry-clean only :evil:


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PostPosted: Tue Sep 22, 2009 4:54 pm 
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Laproscopic Intra-muscular straingauge/eeg implants...


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PostPosted: Wed Sep 23, 2009 12:17 am 
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in the industry

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Location: Melbourne Australia
mythical wrote:
There's only one way to solve this! Mount the new Metrigear pedals onto an old SRM that fits a Ergomo BB. Then have a PowerTap rear hub and to top it off the Polar power meter. Then measure all the data up against each other and see which one comes out most accurate! :twisted:

No matter spending those thousands on power measuring equipment! Personally, I've never needed nor wanted a power meter. I've had ample power at my disposal.



Like this!

Image

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PostPosted: Wed Sep 23, 2009 8:20 am 
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LOL! :exactly: :lol: :popcorn:

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PostPosted: Wed Sep 23, 2009 12:34 pm 
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Location: FRANCE , Les Landes
When you buy it you have a ANT + head unit or you have to buy one ?


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PostPosted: Wed Sep 23, 2009 1:00 pm 
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What's the accuracy? You can have +/- 2% on some power meters but if it's >3 or 4% then it begins to lose it's value. And I don't mean 3% of the actual power, ie the intersection of the y-axis, more whether the value displayed can always deviate by 3%, ie whether the slope is linear, so you never know exactly how comparable your data is. Battery voltage, temperature etc can effect this linearity.


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PostPosted: Wed Sep 23, 2009 4:16 pm 
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In the data sheets I posted they claim 1.5%, which is as good as PowerTap for example.

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Posted: Wed Sep 23, 2009 4:16 pm 


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PostPosted: Wed Sep 23, 2009 11:15 pm 
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I profess to know nothing about this kind of stuff. That said, I'll ask a dumb question: is there any such concept as driveline loss (as in cars) in bike power meters? Or, do they measure power at a specific location, i.e., [x] watts measured at the hub on a powertap is exactly that: [x] watts? Is there a measurable loss of power from crankset to rear wheel due to whatever inefficiency might exist?

Thanks for any intelligent responses. :beerchug:

By the way I like this pedal meter idea though. Sure keeps things simple.


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