Weight Weenies
* FAQ    * Search    * Trending Topics
* Login   * Register
HOME Listings Blog NEW Galleries NEW FAQ Contact About Impressum
It is currently Fri Sep 22, 2017 3:33 am

All times are UTC+01:00





Post new topic  Reply to topic  [ 10 posts ] 
Author Message
PostPosted: Wed Sep 13, 2017 10:25 am 
Offline

Joined: Tue Nov 03, 2009 7:56 pm
Posts: 225
Location: London
I use a number of power meters, and most of them track quite closely (Powertaps, Neo and Computrainer) and generally seem similar in terms of perceived effort.

I recently purchased a Quarq Dfour and this consistently reads about 10-20w higher than the others for a similar effort.

Is this because of the crank vs hub based measurement? Do other brands track closer to the Powertap, such as the Power2max?

Thinking of selling the Quarq because of this.


Top
   
Posted: Wed Sep 13, 2017 10:25 am 


Top
   
 
PostPosted: Wed Sep 13, 2017 10:41 pm 
Offline

Joined: Thu Mar 28, 2013 4:42 pm
Posts: 786
Location: Pa USA
Probably its drivetrain loss that you're seeing. You really should quantify it as a percentage though. All your other systems measure post drivetrain. If you're talking in the area of <5% that's probably it.


Top
   
PostPosted: Wed Sep 13, 2017 10:53 pm 
Offline

Joined: Sun Apr 23, 2017 1:59 pm
Posts: 67
My powertap hub, c1 chainrings, and SRM are all within 1-2% of each other at threshold so far as I can tell. My P2Max seemed to be as well for the 1-2 months I used it.

10-20 watts seems like too much at a threshold, in my opinion, but I guess that'd still be within 3%.

_________________
Cat 1


Top
   
PostPosted: Thu Sep 14, 2017 12:55 am 
Offline

Joined: Thu Mar 28, 2013 4:42 pm
Posts: 786
Location: Pa USA
Another thing, how many rides on the Quarq/ They don't stabilize for until few rides with new rings .


Top
   
PostPosted: Sat Sep 16, 2017 10:56 am 
Offline

Joined: Wed Mar 05, 2014 9:20 pm
Posts: 100
well you can fudge the quarq to read the same as the others using qalvin, repeatability is the main thing to be concerned about.


Top
   
PostPosted: Sat Sep 16, 2017 11:36 am 
Offline

Joined: Wed Jan 10, 2007 10:56 pm
Posts: 1378
Location: Canada
Who knows which is right, without doing a slope test with a known weight. Or you could end up correcting the quarq to the wrong value.

Sent from my SM-G950W using Tapatalk

_________________
My RCA


Top
   
PostPosted: Tue Sep 19, 2017 5:39 pm 
Offline

Joined: Mon May 21, 2012 7:40 pm
Posts: 54
I have a similar issue and trying how to incorporate it into my training. My Stages trainer has a stages crank based power meter. I put on my new Assioma Duos and the pedals read ~10-15 watts lower, almost all the time. I THINK i might have something to do with flywheel, but not sure.

I'm just keeping a mental tab on the fact, but keeping track of TSS is a little annoying. Still, I don't think 10 watts makes a huge impact on TSS over 45-90 minutes.


Top
   
PostPosted: Tue Sep 19, 2017 6:16 pm 
Offline

Joined: Tue May 23, 2006 4:33 am
Posts: 1081
Read up on the SRM website or on YouTube about how to use calibrated-weight iron plates to get an accurate absolute measurement. You'll be able to plot a simple straight line with a y-intercept and calculate your precise slope, which lets your powermeter output the right power for a given load. If you're using multiple devices and worried about differences between them, you should be doing this on a regular basis anyway.


Top
   
PostPosted: Tue Sep 19, 2017 7:10 pm 
Offline

Joined: Thu Mar 28, 2013 4:42 pm
Posts: 786
Location: Pa USA
You can adjust the slope on the quarq which will make it accurate in the absolute sense, but it doesn't seem that the issue posed has to do with that.

He wants his powermeters to be consistent, and doesn't seem to care about accuracy. We could start a whole thread on why that's not the question to ask. I agree that knowing that the quarq is ok is a first step, but their slope out of the box from the factory is supposed to be pretty good. Knowing that the quarq is good though won't tell you a thing about whether another crank based meter will be equally good or "closer" to his other devices.
He states that his pt, neo and computrainer are consistent while his quarq is a bit high. If he's in the range of 5% or so, its likely not much more than normal variability and drivetrain loss. If he's training, obviously he can adjust his target power - if he did his test using the pt he simply needs to set his target x% higher on the quarq when he uses that.

The elephant in the room is that its pretty well accepted that while metabolic ftp doesn't change, indoor trainers exert a greater training load at a given target power. Who knows why, really, but most folks that have been using them for a while accept this. So there's a lot of target adjustment going on.

Yes, if you track TSS or use a training load tracker adjusting all this can be a giant pain, which is why coaches prefer that you use one power meter and stick to it. I've been using pm's since square taper wired srms pretty much it, and its only this month that I've had multiple outdoor systems at the same time. Yeah, its a bit of a pain.


Top
   
Posted: Tue Sep 19, 2017 7:10 pm 


Top
   
 
PostPosted: Tue Sep 19, 2017 9:41 pm 
Offline

Joined: Tue Nov 03, 2009 7:56 pm
Posts: 225
Location: London
Thanks for the replies.

Yes, I assume it is partly drivetrain loss and might need to run in the Quarq a bit more with the new chainrings.


Top
   
Display posts from previous:  Sort by  
Post new topic  Reply to topic  [ 10 posts ] 

   Similar Topics   Author   Replies   Views   Last post 
There are no new unread posts for this topic. Zwatt Power Meters

in Road

dcpdpayne

6

1198

Mon Oct 10, 2016 1:40 pm

reknop View the latest post

There are no new unread posts for this topic. what power meters are you using on a cipollini bond

in Road

mattCSUK

2

279

Sat Jun 24, 2017 7:10 am

mattCSUK View the latest post

There are no new unread posts for this topic. Left and Right sensing light weight power meters

[ Go to page: 1 2 ]

in Road

bpe

20

1915

Mon Mar 06, 2017 10:16 pm

kulivontot View the latest post

There are no new unread posts for this topic. Which is more accurate, generally, smart trainers or crank based power meters?

[ Go to page: 1 2 ]

in Road

Shrike

15

1062

Mon Mar 27, 2017 12:38 am

HakeemT View the latest post

There are no new unread posts for this topic. "Multiple power meters found" issue

in Training

LouisN

6

548

Mon Mar 06, 2017 7:44 pm

LouisN View the latest post


All times are UTC+01:00


Who is online

Users browsing this forum: Yahoo [Bot] and 4 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
Powered by phpBB® Forum Software © phpBB Limited