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Power Meters - Reliability
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explorerJC




Joined: 20 Oct 2005
Posts: 13635
Location: Farthingstone

PostPosted: Fri Feb 24, 2017 6:46 pm    Post subject: Reply with quote

hammerer wrote:
explorerJC wrote:
i can push higher on my turbo and/or can hold a level better because the focus on purely on the data and not every possible distraction, including my brain...


that's maybe part of the reason for higher watts on track to road, no distractions apart from the bunch which is easy to judge as there's no random pace changes, but turbo I'm pushing as hard, if not harder but just don't generate the watts. Really strange and I know people like myself and also the opposite like you.


yep, it's why i used to do well on indoor racing and the records...
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Nobbie




Joined: 24 Jul 2006
Posts: 4392
Location: Wilmslow

PostPosted: Sat Feb 25, 2017 8:59 pm    Post subject: Reply with quote

TriSam wrote:
How big is big? Because of work, I have access to some pretty large mass hangers.

Where do you have to hang it, around the pedal/pedal spindle I'd assume?

What data are you looking for to make sure it's properly calibrated? Thanks


To make it worthwhile you need at least 10kg, preferably more. From memory, 10kg shifts the number by about 100, so you can only measure the accuracy to about +/- 1%

This explains how it's done

http://jibbering.com/sports/power2max-review.html
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Nobbie




Joined: 24 Jul 2006
Posts: 4392
Location: Wilmslow

PostPosted: Sat Feb 25, 2017 9:03 pm    Post subject: Reply with quote

Oranj wrote:
Point to note: Sending your Power2Max back to the factory for recalibration probably won't bring it back in line with other powermeters because (as I understand it) they use a dynamic calibration test - the powermeter is tested under load when rotating. I'm not entirely sure why but this seems to result in the slightly lower power reading that P2M give. It's not a problem if you always use the same powermeter - you are, after all only comparing like-with-like and this is perhaps a more accurate way of calibrating a powermeter as it more closely mimics what's going on in the real world.

A static calibration (hanging a big weight off a crank arm), will, I imagine, have a different effect and maybe restore those missing watts.


When my P2M drifted lower by 5% as measured using a static test, I had discussions with P2M who insisted that it was not an accurate method and nothing was wrong with my unit. I cross checked with a powertap and still found the 5% difference, so I bit the bullet and paid for recalibration. Despite their claims to the contrary, when I got the unit back and did a static test it confirmed that the unit was back in cal.
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TriSam




Joined: 26 Aug 2011
Posts: 1044
Location: Tunbridge Wells

PostPosted: Sun Feb 26, 2017 9:15 pm    Post subject: Reply with quote

Nobbie wrote:
TriSam wrote:
How big is big? Because of work, I have access to some pretty large mass hangers.

Where do you have to hang it, around the pedal/pedal spindle I'd assume?

What data are you looking for to make sure it's properly calibrated? Thanks


To make it worthwhile you need at least 10kg, preferably more. From memory, 10kg shifts the number by about 100, so you can only measure the accuracy to about +/- 1%

This explains how it's done

http://jibbering.com/sports/power2max-review.html


Cheers Nobbie, will have to have a play this weekend before my 3Up TTT!
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TriSam




Joined: 26 Aug 2011
Posts: 1044
Location: Tunbridge Wells

PostPosted: Sun Feb 26, 2017 9:17 pm    Post subject: Reply with quote

One thing I've immediately noticed from that P2M article, is that it says it can measure up to 200RPM. Mine has only ever given readings of up to 187, where it seems to cap.
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