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Power Meters - Reliability
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leahnp




Joined: 25 Jan 2005
Posts: 1888
Location: Scottish Borders

PostPosted: Thu Feb 16, 2017 1:34 pm    Post subject: Reply with quote

i'm using the same power meter as jorgan and i cannot complain about it. if it works and you can get it for 250 grab it
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KingstonGraham




Joined: 21 Mar 2008
Posts: 7559

PostPosted: Thu Feb 16, 2017 4:04 pm    Post subject: Reply with quote

Got a P2M - been on for almost a year in all sorts of weather, and I've never had to think about it. Just works, and has never had any issue.
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TriSam




Joined: 26 Aug 2011
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Location: Tunbridge Wells

PostPosted: Thu Feb 16, 2017 5:06 pm    Post subject: Reply with quote

Yeah I love my P2M, it's incredibly reliable and doesn't need calibration or zeroing. However, it's not the most convenient thing to swap between bikes. If I was to buy again, I would buy a set of Vectors or a PowerTap hub which I would then stick disc covers over for when I race.
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Oranj




Joined: 27 Sep 2007
Posts: 1180
Location: Oxford

PostPosted: Thu Feb 23, 2017 1:04 pm    Post subject: Reply with quote

I started out with a Power2Max, and regret selling it now. German engineering, you can't beat it (although I always had a slight feeling that it was reading about 5-10W down - when I did the post-race analysis I always seemed to be more aero than I thought I was.)

Most of the TT crowd are racing on Quarq, so I bought one of those and a Stages for the training bike. I found the other 5-10W that I was missing from the Power2Max, but the Stages went through two failures before I got my money back and bought a second hand Quarq for the training bike.

Both Quarqs have recently failed - in one the strain gauges inside the spider failed and the other suffered rapid battery drain la Stages. They were both over 2 years old and therefore out of warranty Evil or Very Mad . I was offered half-price replacements, but with the $/ exchange rate the way it is at the moment I declined. Also a 2-year warranty seemed pretty limited on what is supposed to be a fairly high-end piece of tech.

I'm currently running a pair of the generation-2 Garmin Vectors. They seem pretty good so far...
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stenard




Joined: 04 Sep 2013
Posts: 1147

PostPosted: Thu Feb 23, 2017 1:29 pm    Post subject: Reply with quote

Interesting that both Jorgan and Oranj think the P2M reads low. I know from my own experience it was quite a bit lower than the virtual power trainerroad had been estimating beforehand, but that's not really a fair comparison.

Seeing as I'm not intending to change any time soon, then I guess I don't really care if they are reading a tad low. Having said that, DCR's in-depth review had them lined up with other PMs on the market.


I guess the easiest way to test would be to borrow some P1s or a PT rear wheel and do a comparison ride.
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Nobbie




Joined: 24 Jul 2006
Posts: 4394
Location: Wilmslow

PostPosted: Thu Feb 23, 2017 2:11 pm    Post subject: Reply with quote

I know one of mine drifted low by 5% after a year and I had to have it sent back to be calibrated. Must cross check my training P2M with my powertap as a quick reality check.

You can check the P2M calibration by hanging big weights of it.
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TriSam




Joined: 26 Aug 2011
Posts: 1122
Location: Tunbridge Wells

PostPosted: Thu Feb 23, 2017 3:03 pm    Post subject: Reply with quote

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
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Jorgan




Joined: 12 Nov 2007
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PostPosted: Thu Feb 23, 2017 3:08 pm    Post subject: Reply with quote

The Wattbike at work is 5-10w higher than my P2M on 4-5 min intervals. My FTP is still pants though. I need to do some more sessions on both, to get a better comparison; hopefully the delta will reduce with more data.

Both apparatus are consistent though, which is a big plus; it's my fatigue that's the variable.
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stenard




Joined: 04 Sep 2013
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PostPosted: Thu Feb 23, 2017 5:47 pm    Post subject: Reply with quote

Jorgan wrote:
The Wattbike at work is 5-10w higher than my P2M on 4-5 min intervals. My FTP is still pants though. I need to do some more sessions on both, to get a better comparison; hopefully the delta will reduce with more data.

Both apparatus are consistent though, which is a big plus; it's my fatigue that's the variable.


Out of interest, how do you know that? Is this 4-5mins intervals on the wattbike versus equivalent 4-5mins intervals on a trainer at home?

If so, could this be to do with inertia? One of the reasons I've hardly touched my trainer at home recently is that I prefer the inertia feeling of the wattbikes at the gym, which are more representative of outdoor riding I find. I find I can hold marginally less power on my dumb trainer, simply because I'm having to power through the dead spots, which I guess fatigues me a fraction sooner.

I could therefore see an argument that both power meters are accurate. They're just measuring power in different fact patterns. Although to be honest, I've never done enough riding of my own trainer and the gym wattbikes, in the same training blocks, to determine an inconsistency of my relative power levels on each.
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Jorgan




Joined: 12 Nov 2007
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PostPosted: Fri Feb 24, 2017 8:48 am    Post subject: Reply with quote

^^ I think it will take quite a few more rides to get a better picture. Like I say, the inconsistency of my 'freshness' has to be taken into account too.

Interesting point ref the inertia, like you and probably many others, I find it easier to push harder outside where the real world provides more resistance.
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Oranj




Joined: 27 Sep 2007
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PostPosted: Fri Feb 24, 2017 9:01 am    Post subject: Reply with quote

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.
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Jorgan




Joined: 12 Nov 2007
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PostPosted: Fri Feb 24, 2017 9:44 am    Post subject: Reply with quote

Tacx watts are the way ahead apparently Very Happy
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hammerer




Joined: 19 Nov 2007
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PostPosted: Fri Feb 24, 2017 4:28 pm    Post subject: Reply with quote

Jorgan wrote:
Tacx watts are the way ahead apparently Very Happy


Kickr watts are better. Can find about 40 watts there if you want to race in Zwift Wink

I notice a big difference on my KK road turbo and outdoors, 30-40watts higher outdoors. Its not an indoor thing as my rollers are similar to outdoors and at LV Velodrome I can generally get a bit higher still. Might be something to do with the fixed wheel though as at Herne Hill I push a bit higher also than on the road. Again I haven't enough data of all variations to be ultimately sure of the reasons. I use P1's which are just simple and work. pedal wrench on and off in a minute between track, TT and road bikes. Have nothing to compare them to but the figures seem to match expectations with speed.
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explorerJC




Joined: 20 Oct 2005
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PostPosted: Fri Feb 24, 2017 5:30 pm    Post subject: Reply with quote

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...
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hammerer




Joined: 19 Nov 2007
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PostPosted: Fri Feb 24, 2017 6:40 pm    Post subject: Reply with quote

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.
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