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PostPosted: Thu Jun 20, 2013 12:44 am 
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SLC -> Salt Lake City? Does the temperature profile of your rides look like this?

Image

Spinning backwards a few times is not something you'd ideally want to do in the middle of a threshold test. That and when trying to do it quickly, I'd occasionally get some funky results (Quarq S975).

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Posted: Thu Jun 20, 2013 12:44 am 


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PostPosted: Thu Jun 20, 2013 1:09 am 
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airwise: excellent analysis, even using the Ferrari grade adjustment. Fully consistent with DCRainmaker's test. Indeed, I won't criticize his test, but he could have compared analytic power to the recorded powers to put the nail in the coffin of the assertion the Quarq was correct with PowerTap and Stages coincidentally wrong and each consistent with heartrate.

I've plotted analytic power (calculated from altitude, distance, time) with PowerTap on climbs and the two typically agree well, although there's fitting parameters like CdA, Crr, and total mass (typically uncertain to 2 kg or so).

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PostPosted: Thu Jun 20, 2013 3:22 am 
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jmilliron wrote:
SLC -> Salt Lake City? Does the temperature profile of your rides look like this?

Image

Spinning backwards a few times is not something you'd ideally want to do in the middle of a threshold test. That and when trying to do it quickly, I'd occasionally get some funky results (Quarq S975).



I can't say it's identical to that, no. Similar? Yup. And yes, Salt Lake City.

Luckily I don't do a threshold test every ride, so the 3 back spins isn't ruining my ride. Again, I download every ride and havent to this point experienced any drift on long climbs or any other ride for that matter.

Just reporting what I see. I assume you're seeing something different?


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PostPosted: Thu Jun 20, 2013 6:25 pm 
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Airwise- which Quark was this?

Rchung- I suspect you have something in mind. Could you post a pointer to it?


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PostPosted: Thu Jun 20, 2013 8:11 pm 
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RChungs referring to his virtual elevation program/testing protocal.


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PostPosted: Thu Jun 20, 2013 8:58 pm 
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I didn't know it could do that.

Here's a comparison test between PMs using VE: http://www.bikeradar.com/blog/article/t ... als-32678/

it looks like you can compare drift between PMs, but not absolute drift.


Would it be possible to detect drift from a single PM's data by comparing the power to the standard calculated model for multiple segments of a climb? If the PM drifts then the relationship between the real power data and the calculated power would change. You would want to use a climb with consistent grade at the top and bottom, consistent road surface and wind, but a good temperature variation.


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PostPosted: Thu Jun 20, 2013 10:04 pm 
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SLCBrandon wrote:
Luckily I don't do a threshold test every ride, so the 3 back spins isn't ruining my ride. Again, I download every ride and havent to this point experienced any drift on long climbs or any other ride for that matter.

Just reporting what I see. I assume you're seeing something different?


Yes, saw. I've got a ~20 minute climb near my house that's a pretty good control. Rode it a number of times for a year with a PowerTap PRO+ and a number of times the following year with a SRAM S975 Quarq. The PT seemed seemed much more consistent and I didn't have to do any spinning backwards silliness.

Got a new frame at the beginning of this year and my Quarq didn't fit on it. So I sold it. Wasn't bummed.

YMMV.

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PostPosted: Thu Jun 20, 2013 11:35 pm 
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Location: san francisco bay area, ca
Jason, I'm guessing you're talking about Old La Honda. :) I used to ride with a Powertap, but have been riding with a SRAM S975 Quarq the last couple years. I've gotten very inconsistent readings in my power up OLH and on my climbs in general. For some of my rides this year up OLH, I just don't believe the power data at all. It's kind of a bummer when you have no faith in the power data from your power meter... I wasn't really calibrating the Quarq very often, so I now try to consciously manually calibrate it before every ride. I'm going to also try the auto calibration by spinning backwards, but my concern with that has always been whether or not the calibration actually occurs, because there is no indication to let me know if the calibration was successful. I really liked having a Powertap and not worrying about the calibration, but I really like being able to use any wheels I want with the crank-based system. Of course, it's kind of meaningless if you don't trust the data being generated by your crank-based system.... argh...


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PostPosted: Thu Jun 20, 2013 11:55 pm 
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I'm finding anything short of an SRM is going to have its issues/detractors.

Seems everyone of them has their shortcomings or people debating and wondering about their accuracy. I used an iBike Aero for a few years before getting the exogram quarq recently. I still use the iBike head unit as the head unit for the quarq, so I get both data when I download. One thing that has surprised me is how close the iBike actually is.

On things like sprints or other short, high output efforts the ibike is very generous, but steady state climbs or long rides its astonishing how close it is. Last weekend I did a 91mi/8600ft ride and the ibike showed only a 2.2w ave diff.

On a very well known climb in my area it was .9w ave off for 29mins. Now, again, on sprints and other rides its anywhere from 30w ave off (2 min VO2+ efforts) to 200w off peak for sprints.

Anyway, I've been very happy with the quarq so far. Hopefully I don't experience the issues others have.



Ps- the reason I didn't go powertap was because I interchange 2 sets of wheels regularly.


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PostPosted: Fri Jun 21, 2013 12:31 am 
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I have issues with SRM, as well. No reason to believe it's appreciably better than Quarq. For example...

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PostPosted: Fri Jun 21, 2013 12:46 am 
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Good to know, thanks for the link.


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PostPosted: Fri Jun 21, 2013 1:04 am 
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FYI: There's a post on the wattage list related to DCr's stages review and the Quarq temperature drift from a Quarq employee calling out DCr's Quarq as being faulty and that any other users experiencing similar problems should contact customer support.


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PostPosted: Fri Jun 21, 2013 2:17 pm 
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And all of this applies to power meter rumours?

Sure wish you all opened up a new thread so we can get back on the subject.


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PostPosted: Fri Jun 21, 2013 3:45 pm 
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eric wrote:
Airwise- which Quark was this?



Eric it was the Rotor 3d+.


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Posted: Fri Jun 21, 2013 3:45 pm 


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PostPosted: Fri Jun 21, 2013 6:09 pm 
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That's the Cinqo power meter, the older design.
The new one's spec'd to a tighter tolerance of 1.5% vs 2%. For whatever that is worth.


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