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Old 12-12-13, 06:42 AM   #5326
thechemist
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Originally Posted by robabeatle View Post
Sorry if I missed it but can someone point me to a link/thread that discusses how to recalibrate a powermeter? I have a Powertap if that is relevant.
http://www.cyclingpowerlab.com/power...libration.aspx

All of this also brings up a good point in that some may think it is a MAJOR hassle to check calibration/slope. As TR pointed out, it really isen't hard to do. All you need is an ACCURATE weight(20kg is what I will be using with quarq) and like 5 minutes. You can also measure your weight at USPS to see if you can get +-2%.




edit: sorry to hear gsteinb
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Old 12-12-13, 07:23 AM   #5327
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Yea I was curious about that too?

With the new Riken I'm seeing higher numbers then my S975 and that's indoors. I have made adjustments to my FTP moving forward and of course zones for training. It's not very often I look back at what I did power wise and use TT times, general race results and performance in team rides a s measure of progress.

With all that stated, I am never at the pointy end of the race so I feel I can take a less then critical view of these numbers. That, and I have more important things to occupy me mind.

Now if it's a relatively simple process to check accuracy and make adjustments then I'd be into that for sure.
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Old 12-12-13, 07:31 AM   #5328
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http://www.cyclingpowerlab.com/power...libration.aspx

All of this also brings up a good point in that some may think it is a MAJOR hassle to check calibration/slope. As TR pointed out, it really isen't hard to do. All you need is an ACCURATE weight(20kg is what I will be using with quarq) and like 5 minutes. You can also measure your weight at USPS to see if you can get +-2%.




edit: sorry to hear gsteinb
i don't know about you guys, but i wouldn't trust the accuracy of the scale at my local usps.
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Old 12-12-13, 07:36 AM   #5329
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i don't know about you guys, but i wouldn't trust the accuracy of the scale at my local usps.
It would just be to verify your known weight. So if you have 50lbs and USPS weighs it at 50.05 you are good to go.If I recall though, USPS scales have to be pretty accurate per policy. Obviously the better option would be to get a calibrated test weight.
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Old 12-12-13, 07:54 AM   #5330
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My philosophical training is in Cartesian epistemology; do I know with certainty they are 100% accurate to some power number standard that exists somewhere? Not even no, but hell no. But I'm told that they're good enough for government work.
My formal training is in statistics, finance, and engineering. There's a philosophical hurdle that people who work with statistics in the real world have to cross, which is understanding that any measurement and prediction system will have inputs that are inaccurate to some degree, that the resulting inaccuracy of the outputs can be estimated, that the outputs are better than just making stuff up even if the inputs are inaccurate.

Every input has error bars around it: the power meter, what you think your zones are, how your body will adapt to specific work in any given zone, and so on. You want all of the estimates to be as accurate as possible, because that contributes to the effectiveness of the whole system. But in the end they are all estimates.

When you see 300W on a perfectly calibrated PM, most of the time that means you're within 5W of that number, but a meaningful part of the time you are further away. That doesn't mean you shouldn't care if your PM is miscalibrated by 10W, but it does mean that at some point, as gsteinb said...

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Fix what you can and don't worry too much about it. It it what is, move on.
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Old 12-12-13, 08:07 AM   #5331
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My formal training is in statistics, finance, and engineering. There's a philosophical hurdle that people who work with statistics in the real world have to cross, which is understanding that any measurement and prediction system will have inputs that are inaccurate to some degree, that the resulting inaccuracy of the outputs can be estimated, that the outputs are better than just making stuff up even if the inputs are inaccurate.

Every input has error bars around it: the power meter, what you think your zones are, how your body will adapt to specific work in any given zone, and so on. You want all of the estimates to be as accurate as possible, because that contributes to the effectiveness of the whole system. But in the end they are all estimates.

When you see 300W on a perfectly calibrated PM, most of the time that means you're within 5W of that number, but a meaningful part of the time you are further away. That doesn't mean you shouldn't care if your PM is miscalibrated by 10W, but it does mean that at some point, as gsteinb said...
the estimated inaccuracy is certainly quantifiable to a certain degree dependent upon your least accurate variable... but you can make all of your variables less than 2%.
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Old 12-12-13, 08:13 AM   #5332
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Hey, maybe I can derail the holy war with a joke.

A firefighter, an engineer, and a mathematician are in adjoining hotel rooms. Through an amazing coincidence, a small fire breaks out in the wastebasket of each room.

The firefighter sees the fire, rushes into the hall, gets the fire hose, and puts out the fire.

The engineer sees the fire, notices a water glass in the room, does a quick calculation, fills a glass with water from the sink and puts out the fire.

The mathematician sees the fire, notices a water glass in the room, says "trivial!" and goes back to bed.
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Old 12-12-13, 08:21 AM   #5333
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i don't know about you guys, but i wouldn't trust the accuracy of the scale at my local usps.
That's rather unfounded when you don't have proof. The USPS scale gets calibrated every month, and the scales at FedEx and UPS gets an annual check.

all three told me that the weight plates i had were 19.8 lbs.
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Old 12-12-13, 08:27 AM   #5334
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I weighed my stuff at home, at fedex and at the USPS.

home - 48
usps - 47, 15oz
FedEx - 48
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Old 12-12-13, 09:18 AM   #5335
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Thanks much.

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Old 12-12-13, 12:16 PM   #5336
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I think I could make a compelling case for:

Quote:
Originally Posted by rbart4506 View Post
I am never at the pointy end of the race so I feel I can take a less then critical view of these numbers.
False

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Originally Posted by rbart4506 View Post
I am always at the pointy end of the race so I feel I can take a less then critical view of these numbers.
True

Last edited by Racer Ex; 12-12-13 at 12:24 PM.
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Old 12-12-13, 12:19 PM   #5337
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That's rather unfounded when you don't have proof.
Who needs proof when you have a perfectly good ignorance to fall back on?
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Old 12-12-13, 12:27 PM   #5338
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Hey, maybe I can derail the holy war with a joke.

A firefighter, an engineer, and a mathematician are in adjoining hotel rooms. Through an amazing coincidence, a small fire breaks out in the wastebasket of each room.

The firefighter sees the fire, rushes into the hall, gets the fire hose, and puts out the fire.

The engineer sees the fire, notices a water glass in the room, does a quick calculation, fills a glass with water from the sink and puts out the fire.

The mathematician sees the fire, notices a water glass in the room, says "trivial!" and goes back to bed.
My response:

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Old 12-12-13, 12:36 PM   #5339
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stfu MDcatV, if you'd spend less time fooling around on bf and more time calibrating your powermeters, maybe you'd win a race more than once every 6 years.
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Old 12-12-13, 01:08 PM   #5340
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Who needs proof when you have a perfectly good ignorance to fall back on?
And there are times when ignorance is bliss
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Old 12-12-13, 01:22 PM   #5341
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Guys, if all else fails just calibrate your power to your weight on known Strava hillclimb segments.
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Old 12-12-13, 01:28 PM   #5342
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^meh http://alex-cycle.blogspot.com/2013/07/windbags.html
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Old 12-12-13, 04:53 PM   #5343
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you know I only mention strava for the outbursts of haters. don't bite and take it too literally.
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Old 12-12-13, 05:23 PM   #5344
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Strava!!!
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Old 12-12-13, 05:24 PM   #5345
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Strava!!!
Watch the profanity...
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Old 12-12-13, 05:33 PM   #5346
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Watch the profanity...
ahhahahaha. I sometimes yell "strava" on group rides when I see someone attack the group for no reason. I usually start chuckling so hard its hard to contain myself.

When I first got it, I was going around Strava 'huntin'. Now I just do rides and watch progress.
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Old 12-12-13, 06:03 PM   #5347
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Strava!!!
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Old 12-12-13, 06:07 PM   #5348
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you know I only mention strava for the outbursts of haters. don't bite and take it too literally.
I almost fell for it..
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Old 12-12-13, 06:09 PM   #5349
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I calibrated 3 SRM's this afternoon.
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Old 12-12-13, 06:10 PM   #5350
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I almost fell for it..
don't feel bad. sometimes you're the tortoise, sometimes you're the wombat.

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