Shimano power meter inaccuracy, and assymetry

Discuss light weight issues concerning road bikes & parts.
eins4eins
Posts: 124
Joined: Wed Sep 28, 2016 11:49 am

by eins4eins

I'm a happy quarq user, but wonder if this whole inaccuracy discussion isn't overrated. Looks like someone wanting some extra clicks for his youtube channel.
Ineos, Bora, FDJ, Jumbo - all using those cranks. If its good enough for them, how big of a problem could there be?

TobinHatesYou
Posts: 4310
Joined: Mon Jul 24, 2017 12:02 pm

by TobinHatesYou

eins4eins wrote:
Mon Oct 07, 2019 8:00 am
I'm a happy quarq user, but wonder if this whole inaccuracy discussion isn't overrated. Looks like someone wanting some extra clicks for his youtube channel.
Ineos, Bora, FDJ, Jumbo - all using those cranks. If its good enough for them, how big of a problem could there be?

If you think GPLama is reliant on YouTube channel views as a revenue stream, then 1) you don’t know Lama and 2) you don’t understand how little money channels of that size make.

by Weenie


eins4eins
Posts: 124
Joined: Wed Sep 28, 2016 11:49 am

by eins4eins

Yes, don't know all that. But doesn't matter, as my core statement was: how could this be a big issue, if the best professional athletes have no problem with it?
This discussion is totally blown out of proportion in my opinion.

zirxo
Posts: 185
Joined: Wed Mar 19, 2014 12:46 pm

by zirxo

Because as we saw with Sky and left only Stages, the big teams ride what the sponsors wants them to ride. It's as simple as that.

Nefarious86
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by Nefarious86

zirxo wrote:Because as we saw with Sky and left only Stages, the big teams ride what the sponsors wants them to ride. It's as simple as that.
Then train on SRM and Quarq lol

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RocketRacing
Posts: 937
Joined: Thu May 10, 2018 2:43 am

by RocketRacing

eins4eins wrote:
Mon Oct 07, 2019 10:13 am
Yes, don't know all that. But doesn't matter, as my core statement was: how could this be a big issue, if the best professional athletes have no problem with it?
This discussion is totally blown out of proportion in my opinion.
Power meter accuracy is not that key. You just need consistency. But i figure that if i buy a power meter... i want an accurate one. Or at least shimano should come clean with the true accuracy %.

As someone suggested prior, expect shimano to release symmetrical cranks next gen.

BdaGhisallo
Posts: 2324
Joined: Wed Mar 17, 2004 1:38 pm

by BdaGhisallo

RocketRacing wrote:
Thu Oct 10, 2019 2:31 am
eins4eins wrote:
Mon Oct 07, 2019 10:13 am
Yes, don't know all that. But doesn't matter, as my core statement was: how could this be a big issue, if the best professional athletes have no problem with it?
This discussion is totally blown out of proportion in my opinion.
Power meter accuracy is not that key. You just need consistency. But i figure that if i buy a power meter... i want an accurate one. Or at least shimano should come clean with the true accuracy %.

As someone suggested prior, expect shimano to release symmetrical cranks next gen.
PM accuracy is key unless you only plan to ever use one powermeter. If you ever change PM's don't you want to be able to use your previous power levels as a guide? Is it good if one PM reads 300W as being 280W and another as 310W?

velolive
Posts: 21
Joined: Sun Sep 09, 2018 6:49 pm

by velolive

zirxo wrote:
Mon Oct 07, 2019 11:39 am
Because as we saw with Sky and left only Stages, the big teams ride what the sponsors wants them to ride. It's as simple as that.
A bit offtopic :wink:

Sockman
Posts: 32
Joined: Mon Jun 17, 2019 1:58 pm

by Sockman

I own a Shimano PM. It reports the same power numbers as my Quarq, my old P2M & my past two smart trainers. Where exactly does the innacuracy come in?


TobinHatesYou
Posts: 4310
Joined: Mon Jul 24, 2017 12:02 pm

by TobinHatesYou

Sockman wrote:
Thu Oct 10, 2019 3:50 pm
I own a Shimano PM. It reports the same power numbers as my Quarq, my old P2M & my past two smart trainers. Where exactly does the innacuracy come in?

Considering you can’t use a Quarq or P2M at the same time as a Shimano crank based PM, how do you even know? Magic?

spud
Posts: 816
Joined: Sat Feb 07, 2009 5:52 am

by spud

^ you can correlate with the smart trainers

TobinHatesYou
Posts: 4310
Joined: Mon Jul 24, 2017 12:02 pm

by TobinHatesYou

spud wrote:
Thu Oct 10, 2019 5:12 pm
^ you can correlate with the smart trainers

As always, not that simple. Testing two power sources at once doesn’t tell you which one is accurate, if either. Removing and remounting a bike can upset a trainer’s calibration. Average watts over an entire ride doesn’t tell the whole story. In other words there is always a doubt over whether the known good quantity is actually good at one time or another.

For a while I was using a pedal PM, smart trainer and a Quarq, all recording to different head units and uploading the FIT files to DCR Analyzer.

More data is better though. If he could run some concurrent tests and FIT files with, say the same ERG workout, I could upload them to the analyzer tool and we could start making some assumptions.

Hexsense
Posts: 953
Joined: Wed Dec 30, 2015 12:41 am

by Hexsense

Sockman wrote:
Thu Oct 10, 2019 3:50 pm
I own a Shimano PM. It reports the same power numbers as my Quarq, my old P2M & my past two smart trainers. Where exactly does the innacuracy come in?
They need dynamic compensation. To do so, they need to change offset values based on crank angle multiple time a circle.
And even so, it'll only accurate if your pedaling circle is "standard" as there can be some left/right interference, left over momentum etc which isn't equalize to situation they measure and collect the data to create dynamic offset values.

If you get accurate value, good then. But why risking accuracy issue when you can buy power meter that doesn't have to do all these assumption to be accurate.

TheRich
Posts: 472
Joined: Tue Jan 01, 2019 1:36 am

by TheRich

Hexsense wrote:
Thu Oct 10, 2019 8:28 pm
They need dynamic compensation. To do so, they need to change offset values based on crank angle multiple time a circle.
And even so, it'll only accurate if your pedaling circle is "standard" as there can be some left/right interference, left over momentum etc which isn't equalize to situation they measure and collect the data to create dynamic offset values.

If you get accurate value, good then. But why risking accuracy issue when you can buy power meter that doesn't have to do all these assumption to be accurate.
There IS a way to check the accuracy of a power meter, but it doesn't involve using it as a power meter.

Apparently, almost all the crank based meters that GPL tested are just as wrong as Shimano, but somehow the problem is with Shimano.

Kinda baffled why a 1-2% is somehow critical. Oh, you were actually doing 300w and it read 306w, who cares? Worried about your TSS being off by 1 or 2 points? Is there some huge difference in effort that this critical error hides?

Edit: If you want a legitimate gripe, talk about the price.

by Weenie


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