Is your power meter rubbish? New scientific study on accuracy and precision.

Discuss light weight issues concerning road bikes & parts.
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sussexhills
Posts: 53
Joined: Fri Nov 18, 2016 10:31 am

by sussexhills

This is interesting, unless anyone more technically minded than me can find a flaw with the methodology.

Most of the big players were subject to testing and only a handful are actually within the manufacturers stated accuracy. Luckily my Quark comes out ok (in the middle of the best performers), Stages have a proper rinsing though.

https://roadcyclinguk.com/how-to/fitnes ... think.html

bilwit
Posts: 818
Joined: Sun Apr 03, 2016 5:49 am
Location: Seattle, WA

by bilwit

It's interesting. Like the article, I wouldn't be worried too much about the the accuracy in regards to "true" power output unless you are, for some reason, comparing the output between multiple separate units. Otherwise, the results are normalized to your unit and bike (a "300w" to you will mean something slightly different to someone else, but that would always be the case given that everyone has different fitness levels). Having multiple bikes equipped with PMs would be a concern though when riding to power. Only way to be for-sure is to treat the numbers separately (ie. measure each effort based off of separate FTP on both bikes/PMs).

The most alarming thing in the article is the variation with the exact same unit. Stages loses out here again, but the article admits (and shows) that many were precise while a few weren't. They tested 12 SRM, 10 PowerTap, 11 Quarq, 13 Stages, 3 Verve, 2 Power2Max, 1 Garmin, 1 Polar, 1 Rotar. Was the testing sample large enough to conclude that this behavior is systemic or they just had a few defective ones (4 out of 13 of the Stages had over 2% variance in the individual precision test)?
Last edited by bilwit on Thu Aug 24, 2017 11:46 pm, edited 1 time in total.

by Weenie


mag
Posts: 149
Joined: Thu Mar 16, 2017 12:23 pm

by mag

It seems it's the same study that was discussed here viewtopic.php?f=3&t=54198&start=3120#p1315887

TobinHatesYou
Posts: 1498
Joined: Mon Jul 24, 2017 12:02 pm

by TobinHatesYou

It's a pretty shitty "study" that lumps multiple versions of branded PMs as one. The sample sizes are also way too small, especially for any brands outside the top 4.

fasdflkjweorinjs
Posts: 25
Joined: Sun Mar 23, 2014 6:25 am

by fasdflkjweorinjs

Who cares about 4%


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Kaboom
Posts: 118
Joined: Wed Mar 22, 2017 3:53 pm

by Kaboom

fasdflkjweorinjs wrote:Who cares about 4%


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So long as it is always either 4% or -4% that's fine, but if the precision is off and it can vary from -4 to +4 from ride to ride, a 350w interval can go from being 334w to over 366w. That's a 32watt spread. Not at all insignificant.

by Weenie


Rubik
Posts: 104
Joined: Sun Apr 23, 2017 1:59 pm

by Rubik

bilwit wrote:It's interesting. Like the article, I wouldn't be worried too much about the the accuracy in regards to "true" power output unless you are, for some reason, comparing the output between multiple separate units.


Which you'll be doing when you get a new powermeter.

Accuracy matters because when you get that new powermeter, if it's different than your previous one than you're essentially starting over with all your power data. Which is hors categorie suckitude.

A big reason I won't touch a one-sided powermeter with a stick.
Cat 1

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