SRM adjustment.

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okr
Posts: 273
Joined: Sun Jan 25, 2004 3:55 pm
Location: Norway

by okr

I have just purchased an used SRM amateur, but it seems to be incorrect. Have done some estimations on analyticcycling.com with numbers from hills, and it is off by 10-20% I have calibrated the offset quite a few times, and it is stable. Have been in contact with srm in germany aswell, but thought maybe some of you guys had some tips.

by Weenie


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pinkpanther
Posts: 126
Joined: Tue Jun 06, 2006 4:35 am

by pinkpanther

have you calibrate it before the ride and pushed the set button afterwards?

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simon
Resident Pro
Posts: 1718
Joined: Mon Apr 18, 2005 9:34 am

by simon

i have a mannual here to readjust the slope of the crank. it will take some time(have to do this with my tt bike's srm in the next days)and is a bit complicated if english is not what you're best at.
pm me your e-mail address, i'll send it to you.
from what paul köchli, once ds of lemond and hinault, now swiss srm distributor and "powermeter legend", told me, if you send your crank to srm, they do the same with it, but they have a machine doing what you have to do step by step with my mannual.
everyone interested can give me his mail address, this paper is no secret, it just isn't on the srm homepage.

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pritchet74
Posts: 1076
Joined: Tue May 30, 2006 10:38 pm
Location: NorCal

by pritchet74

I have heard a lot of people say that SRM doesn't do a good job calibrating their own powermeters. I have had my done by them 2x & both times it wasn't done correctly. When I got it new the slope was labeled as 21.7. The power numbers seemed too low by about 20W so I checked the slope myself & came up with 19.2!

That was about 18 months ago. I checked my slope a couple of months ago & it had drifted to 19.0. Last week I got the PM back from SRM (battery change & calibration) & they had the slope as 20.7!

I am very confident in my calibration due to numerous field tests.

Bottom line: be sure to check it yourself!

zakeen
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Joined: Wed Jan 26, 2005 9:13 pm
Location: Australia/Czech-Rep.
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by zakeen

pritchet74 wrote:I am very confident in my calibration due to numerous field tests.

Bottom line: be sure to check it yourself!


I think the most important thing about you doing it yourself is, you do it the same way everytime, it could be wrong(Im sure your not). But you will do it consistent, which is the most important thing about a powermeter. Where at SRM they could have new staff or maybe two different guys do it differently, we dont know.

Does it matter if its 50watts off? No but just make sure its always 50watts off.

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LarsEjaas
Posts: 239
Joined: Sun Jan 21, 2007 10:52 am
Location: Aarhus, Denmark

by LarsEjaas

Hi

Sorry for posting in this old thread - You guys just seem to know a lot about the subject :wink:

I have had my SRM amature powermeter for around 3½ years now, and have always just trusted the yearly calibration done by SRM in Germany.

Well, with all the treads on different forums around the Internet which states that the factory calibration MAY be off + that I SEEM to have gotten stronger (but my numbers seems consistent with last year) I thought it was time to do a little calibration myself ;-)

Anyway - I think I got the basics covered - just got a couple of additional questions that I was hoping some of the knowledgeable people of this forum could answer:

Is ONE weight enough? How heavy should it be?

To make calibration every 3 months easy, I would buy a 10 kg. weight – get it weighted on an accurate scale to make sure the weight is accurate – and then just use this when it's time to get the calibration done.

Do I really have to buy 3 separate weights to get the accuracy of the calibration good enough?

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okr
Posts: 273
Joined: Sun Jan 25, 2004 3:55 pm
Location: Norway

by okr

i use a 5kg weight, i believe it is sufficient... Do three measurements on each side, alternating between the sides, with the same weight.

BdaGhisallo
Posts: 3270
Joined: Wed Mar 17, 2004 1:38 pm

by BdaGhisallo

I believe SRM recommend an absolute minimum of a 20kg load to do the calibration. It's even better if you can do it twice with 20kg and then with 40kg to compare.

Check the Wattage forum and do a search. There is LOTS there about calibrating SRM powermeters.

http://groups.google.com/group/wattage

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LarsEjaas
Posts: 239
Joined: Sun Jan 21, 2007 10:52 am
Location: Aarhus, Denmark

by LarsEjaas

Thanks for the help - I think I got the help I needed at the Google Wattage list - but thanks anyway :-)

by Weenie


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