SRM slope drift
- Thread starter yzfrr11
- Start date
yzfrr11 said:
I'm (almost) scared to answer in case Bozy gets upset again. But, yes it's quite common, and sometimes they're not well calibrated from the factory. There's instructions on the SRM site for how to calibrate your cranks http://www.srm.de/Online_Manual/SRM_English_Manual/PMCalibrate.htm
Why the suspicion and no verification?yzfrr11 said:
It doesn't take that long to check it. You need a weight, an accurate scale, an old inner tube to help hold the wheel, a very sturdy workstand to hold the bike plus the weight, and something to attach the weight to the bike.
The one thing is with the measurement, they say use a pedal blank. Anybody use these? Should we be measuring the weight of our pedals?
Here is my data from a sample of N=1.yzfrr11 said:
From memory (not at home)
The factory calibration was 21.8.
I did the static calibration and got 19.3. This would make my power numbers go higher versus the 21.8.
I repeated the static calibration after two months. I got 19.8. This made my numbers go down a bit from when the slope was 19.3.
I need to do this again this month so will let you know if I remember.
Ric-I'm pleased to hear that you're now so sympathetic to my feelings! For the Forum's readers information the entire SRM calibration tale is more complex than stated by Ric.ric_stern/RST said:
Not too long ago Ric advised me to calibrate a completely new, unused, problem-free SRM prior to its installation. At that time I took his advice at face value (more's the fool me); since the procedure is complicated and time consuming, I had this done professionaly. It was pricey and absolutely unnecessary.
Having said that, if an SRM is giving erratic Wattage results, recalibration should in fact be done-Ric is right in a such a case (even a broken clock tells the right time twice a day!)
Furthermore, I am now informed that in the USA, SRM headquarters in Colorado will perform this arduous procedure quickly and gratis.
bozy said:
i'll state again, it is woth doing straight away when you purchase an SRM. You may have been lucky that yours was correct, but many SRM Amateurs (especially) aren't well calibrated from the factory.
Ric
No fact based study can be found to support Ric's contention that SRM's are not properly calibrated at manufacture.ric_stern/RST said:
The problem is, that as the vendor of a competing power meter (Power Tap-whose problems form many of this forum's posts!), Ric has a conflict of interest in his statements regarding any other products. Though he styles himelf as a "Super-Moderator," he is, in fact, a super entrepreneur, and all his pronouncements must be interpreted with this in mind.
It would be most interesting for the Forum members to know what his financial interest is in this forum itself!
Ric-do you use your influence to censor this forum?
bozy said:
I have no idea why i'm trying to discuss something with someone who is incapable, but as i mentioned before try the Gardner paper. Or see the numerous issues here or on the Wattage list, or alternatively, even Uli Scroberer (apologies on spelling) has said the same thing.
Ric-the duty of a Moderator is precisely to help the forum members regardless of their capabilities. I'm sure the same is expected of a "Super-Moderator."ric_stern/RST said:
Please give us the precise reference to "the Gardner paper."
As you know the SRM factory categorically denies your allegations regarding the need to recalibrate new, properly functioning units, Amateur or Pro.
As you also know, my own experience also flies in face of these aspersions.
bozy said:
i gave it you before and you dismissed as it being worthless (or some similar comment). I'm sure you're able to do a Pub-Med search.
See Beerco's response here http://www.cyclingforums.com/showpost.php?p=1894290&postcount=56 from the "power meters and pedalling effectiveness" thread, where people have contacted SRM about their meters. You seemed to conveniently ignore that message.
And there are similar reports if you trawl the Wattage list at Topica (about people contacting SRM).
And it seems like a couple of people in this thread have already had to check their units.
Ric
Just to add my 2 cents worth.
Here in Australia the AIS get theirs recalibrated every 6 months.
I had mine done recently because the readings looked like they were indecline and I had the battery replaced in the powercontrol.
With the calibration the change was 0.4HZ and speaking with distributor this more likely through the method used here in aussie to do the calibration, it normally results in this magnitude of difference. My unit is 3 years old.
All up the cost was $au240 including the battery change. This in my opinion is not bad.
Bear
Here in Australia the AIS get theirs recalibrated every 6 months.
I had mine done recently because the readings looked like they were indecline and I had the battery replaced in the powercontrol.
With the calibration the change was 0.4HZ and speaking with distributor this more likely through the method used here in aussie to do the calibration, it normally results in this magnitude of difference. My unit is 3 years old.
All up the cost was $au240 including the battery change. This in my opinion is not bad.
Bear
I have never received a proper reference to the paper (or article?) by Gardiner. I would need more information to reference it.ric_stern/RST said:
Beerco's post is interesting, but inaccurate, and doesn't address the need for calibrating new, properly functioning SRM's. His allegation that the SRM Amateur has two strain gauges and the Pro eight gauges is incorrect. The Pro has four gauges. As a result, the wattage readings put out on the Pro are "smoother" than the Amateur. This may explain why a misinformed observer (or even a "Super-Moderator") may mistakenly feel the need to recalibrate the unit even when new!
That units in use may need recalibration is too well known to be commented on.
bozy said:
yes you did. your reply was "As far as the MSSE paper by Gardner you cite, I feel it’s interesting but irrelevant as regards the question I posed in the forum"
so you either read it, or lied previously.
i know it had four - i corrected him in the subsequent post. my point was about his comments that others have contacted SRM about poorly calibrated SRMs direct from the factory.
smoother?
as do new units.
ric
Given the relative rarity of SRM's there are few studies at all on SRM's. The anectdotal evidence from end users and some dealers that I have spoken with is that the dynamic factory calibration does not match static calibration done by end users. My personal experience with calibration is that it is a very straightforward process once one has all the items I listed above.bozy said:
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