New Quarq does not match P1 Pedals

Jul 3, 17 10:40

Post #1 of 26 (3569 views)

I got a new tri bike last week and I had a Quarq w/ Rotor aero chainring installed, mostly because this is a purportedly aero combination with the closed spider. I have been using PowerTap P1 pedals for the last ~1.5yrs, and before that always used PowerTap wheels w/ a brief foray into an SRM for a year. Anyhow, I noticed in my first couple trainer rides that harder efforts appeared to produce a significantly higher than normal power reading on the Quarq, then I did a long ride last Thursday where my average power for almost 6hrs was only ~15W shy of my best 1hr power for the year. So today I built an interval workout in Garmin Connect, downloaded it to a 735XT and a Garmin Edge 510, connected the 510 to the Quarq and the 735XT to my PowerTap Pedals, synchronized the start of the workout, and set off to see what happened. Here goes:

5min warmup: 84W Quarq, 80W P1 (P1/735XT seemed to take a bit before it read anything other than zero, so wasn't too worried about this).

2min interval: 177W Quarq, 176W P1 (dang, maybe I did get a ton faster!)
3min recovery: 109W Quarq, 107W P1

2min interval: 205W Quarq, 198W P1 (3.5% difference, could be worse)
3min recovery: 98W Quarq, 90W P1 (yikes, that's ugly)

2min interval: 234W Quarq, 222W P1 (5.4% difference, no longer acceptable!)
3min recovery: 84W Quarq, 75W P1 (more than 10%!)

2min interval: 260W Quarq, 244W P1 (6.5% difference, keeps getting worse!)
3min recovery: 114W Quarq, 102W P1 (still more than 10%!)

2min interval: 277W Quarq, 261W P1 (6.1% difference)

After this I decided to hop off the bike and recalibrate each power meter. The Quarq didn't change much, remained in the 280s, the PowerTap went from 10->5. I suspect that isn't a huge change, but don't really know. Recalibrating on the 735xt required stopping the interval session, so I was no longer synced up. I did manage to do one more synced interval up a hill after the recalibration which resulted in 271W for the Quarq vs 259W for the P1 (4.6% difference).

I'm just curious if anyone has any ideas on something I should do to try and sync them more closely? Or at least get the percentage difference to be more consistent? Also wondering if there are opinions on which is more accurate? My bias is that the PowerTap is likely more accurate. I'm disappointed to have this trouble, I had read a fair bit of DC Rainmaker's reviews on power meters and it seemed most power meters are reading within 2-3% of each other across brands in his experience. I want to be able to move back and fourth between bikes seamlessly, so leaving the issue as-is probably doesn't work for me.

Dimond Bikes Superfan

Re: New Quarq does not match P1 Pedals [ericlambi] [ In reply to ]

Jul 3, 17 11:14

Post #2 of 26 (3534 views)

you want apples and oranges to taste the same?

Re: New Quarq does not match P1 Pedals [jkhayc] [ In reply to ]

Jul 3, 17 12:32

Post #3 of 26 (3491 views)

jkhayc wrote:

you want apples and oranges to taste the same?

Helpful response, thanks. Pretty sure this is apples to apples.

Dimond Bikes Superfan

Re: New Quarq does not match P1 Pedals [ericlambi] [ In reply to ]

Jul 3, 17 12:37

Post #4 of 26 (3482 views)

hmm. no, this is an apples to oranges comparison. you are trying to get two different types of powermeters to ''sync up.'' they read at difference places on your bike, right?

personally i trust, in order:

(SRM) - never used one though
Powertap Hub
Quarq
Garmin Vector
Powertap P1s - never used them though
Powertap C1s - never used them though
Stages

Each of those read differently so your desire to have two different powermeters ''sync up'' is inherently flawed.

Re: New Quarq does not match P1 Pedals [ericlambi] [ In reply to ]

Jul 3, 17 12:44

Post #5 of 26 (3471 views)

As per DCR's tests, I think it is normal for some variation, but 10% does seem like a lot! Whichever you are going with, I guess as long as its consistent with itself?

Question - why the second PM? Not happy with the Powertaps?

Re: New Quarq does not match P1 Pedals [ericlambi] [ In reply to ]

Jul 3, 17 12:50

Post #6 of 26 (3460 views)

why don't you sell the quarq buy the same crank without a quarq and just switch the pedals back and forth and not worry about it. isn't' that what you said you wanted to do anyway in the last paragraph?

2019 T-Rex Tri Series

Last edited by: mknight84: Jul 3, 17 12:50

Re: New Quarq does not match P1 Pedals [ericlambi] [ In reply to ]

Jul 3, 17 12:57

Post #7 of 26 (3439 views)

mknight84 wrote:

why don't you sell the quarq buy the same crank without a quarq and just switch the pedals back and forth and not worry about it. isn't' that what you said you wanted to do anyway in the last paragraph?

What this guy said. Rotor makes an aero spider or go even more aero with the rotor flow cranks.

I'll take that quarq off your hands and test it against my PMs to verify it's consistency.

Re: New Quarq does not match P1 Pedals [ericlambi] [ In reply to ]

Jul 3, 17 13:00

Post #8 of 26 (3432 views)

I would suggest you check the calibration of the quarq (not talking zero offset here). I assume you can do the same for the pedals.

That will tell you everything you need to know.

Re: New Quarq does not match P1 Pedals [ericlambi] [ In reply to ]

Jul 3, 17 13:45

Post #9 of 26 (3386 views)

It looks like one or both is drifting. I wouldn't worry about the recovery intervals being off I mean you're doing 80 watts.

That said no it's not apples to apples they are different powermeters measuring at different points.

Also you didn't recalibrate them you adjusted the zero offset. It's possible one may not be calibrated correctly.

Re: New Quarq does not match P1 Pedals [ericlambi] [ In reply to ]

Jul 3, 17 13:51

Post #10 of 26 (3380 views)

Just to verify for the new bike did you calibrate the crank arm length for the P1 pedals to match the new bikes crank arm length?

Re: New Quarq does not match P1 Pedals [ericlambi] [ In reply to ]

Jul 3, 17 14:06

Post #11 of 26 (3362 views)

I have been riding P1 for a year & have never seen a calibration of 10. Mine usually runs 5-6. Was the P1 not calibrated correctly to begin with? That is a big difference from before & after the ride.

Re: New Quarq does not match P1 Pedals [SBRcoffee] [ In reply to ]

Jul 3, 17 15:24

Post #12 of 26 (3314 views)

SBRcoffee wrote:

Question - why the second PM? Not happy with the Powertaps?

I wanted to run the speedplay aero pedals, mostly because of the lower stack. I've had good luck with the PowerTap pedals, though maybe they are cutting me short on my top end power!

Dimond Bikes Superfan

Re: New Quarq does not match P1 Pedals [tyme] [ In reply to ]

Jul 3, 17 15:27

Post #13 of 26 (3304 views)

tyme wrote:

Just to verify for the new bike did you calibrate the crank arm length for the P1 pedals to match the new bikes crank arm length?

I did.

Dimond Bikes Superfan

Re: New Quarq does not match P1 Pedals [turningscrews] [ In reply to ]

Jul 3, 17 15:42

Post #14 of 26 (3282 views)

turningscrews wrote:

I have been riding P1 for a year & have never seen a calibration of 10. Mine usually runs 5-6. Was the P1 not calibrated correctly to begin with? That is a big difference from before & after the ride.

I doubt this is an issue. Both of mine have more typically been ~15, but I think this moves with environmental factors (temp, humidity, etc)

I think the thing to do next is dust off my PowerTap wheel and run it vs the others to see what happens. Though it appears I might be SOL in terms of doing anything that could make the two PMs more consistent. I could maybe replace the Quarq w/ the Power2Max if I become confident the Quarq is the issue, or ditch the pedals and go back to the wheel on the older bike if they are the problem, especially since I don't plan to race it anymore.

Dimond Bikes Superfan

Re: New Quarq does not match P1 Pedals [ericlambi] [ In reply to ]

Jul 3, 17 21:50

Post #15 of 26 (3160 views)

My power2max is 3-4W higher than my p1 pedals. Consistently though in the 200-360 range. But I also run q rings so maybe it's the difference in how they both adjust for that

ericlambi wrote:

turningscrews wrote:

I have been riding P1 for a year & have never seen a calibration of 10. Mine usually runs 5-6. Was the P1 not calibrated correctly to begin with? That is a big difference from before & after the ride.

I doubt this is an issue. Both of mine have more typically been ~15, but I think this moves with environmental factors (temp, humidity, etc)

I think the thing to do next is dust off my PowerTap wheel and run it vs the others to see what happens. Though it appears I might be SOL in terms of doing anything that could make the two PMs more consistent. I could maybe replace the Quarq w/ the Power2Max if I become confident the Quarq is the issue, or ditch the pedals and go back to the wheel on the older bike if they are the problem, especially since I don't plan to race it anymore.

Re: New Quarq does not match P1 Pedals [ericlambi] [ In reply to ]

Jul 3, 17 22:24

Post #16 of 26 (3143 views)

My P1s are typically 11-14, my girlfriend's P1s are typically 7-10.

I've run my P1's against my P2Max and found a consistent 3-4 watt difference across a variety of wattages, though short recovery intervals can sometimes be quite different.

However, I purchased a C1 and that varied in a similar way to the way that you are experiencing. Sometimes at 280watts over 10 minutes there would be a 5 watt difference and sometimes there would be a 20 watt difference. I exchanged the C1 for a replacement (after showing powertap the files) and the replacement behaved the same way. I sent the C1 back and paid to upgrade it to a second pair of P1s, which track true with my P2Max.

Comparing two power meters, whilst maybe not an apples to identical apples comparison, I don't believe is an apples to oranges comparison, as someone suggested above. One brand of apple to a different brand of apple more like. They'll taste slightly different, but actually fairly similar.

Re: New Quarq does not match P1 Pedals [rmt] [ In reply to ]

Jul 3, 17 23:13

Post #17 of 26 (3123 views)

ericlambi wrote:

I'm disappointed to have this trouble, I had read a fair bit of DC Rainmaker's reviews on power meters and it seemed most power meters are reading within 2-3% of each other across brands in his experience. I want to be able to move back and fourth between bikes seamlessly, so leaving the issue as-is probably doesn't work for me.

Sadly, this is part of the problem. Those reviews lead people to believe that there is not much differentiation between meters, but they fail to consider a number of use cases.

Matching average power over longer durations is a pretty low bar, but things get more interesting (and out of whack) when some of the variables are rapidly changing (rapid cadence/torque changes, shorter durations).

In your case, though, in addition to trying to compare different meters you also seem to have an issue where one (or both) meters may be operating out of spec. It is for this reason that a static calibration of slope is advisable. It only takes a few moments when you know how to do it (and have a calibrated mass), and it can help to determine which meter is the source of the problem (or if it is both).

I recommend that anyone who is serious about training with power buy a power meter that can be calibrated at home -- and to actually do so on a regular basis (e.g. every 6 months -- or at least once a season when you know you have a stable meter).

rmt wrote:

Comparing two power meters, whilst maybe not an apples to identical apples comparison, I don't believe is an apples to oranges comparison, as someone suggested above. One brand of apple to a different brand of apple more like. They'll taste slightly different, but actually fairly similar.

the only reason this is true is because consumers have accepted two things:
1: that consistency to itself is the only thing that matters in a power meter (wrong: accuracy is important, because people switch brands, get warranty replacements, etc.); and
2: that every meter is as consistent as "the gold standard" (wrong: many companies simply copied accuracy claims (SRM was the first out there with verified accuracy) because they knew consumers would not be sophisticated enough to call them on it.)

it's unfortunate that both of these get repeated so often that many users wind up saving money in the short term (if two things advertise the same features but one costs less, we'd be fools to go for the more expensive one, right?) -- but they don't know how it will cost them until years down the road.

the OP's issue is a classic example of this, unfortunately.

Re: New Quarq does not match P1 Pedals [tetonrider] [ In reply to ]

Jul 4, 17 2:24

Post #18 of 26 (3083 views)

I agree. I was making the point to the poster above who said that comparing two power meters is an apples to oranges comparison. It isn't. They are unlikely to be identical, due to losses in the drive train etc, but they *should* be within a few watts of each other. There's no excuse for them to be out by more than that. I guess theoretically if one was measuring 2% high and the other 2% low, that would be 12 watts at 300 watts but that has to be the maximum allowable discrepancy, and the difference should, as a percentage, remain constant.

Re: New Quarq does not match P1 Pedals [jkhayc] [ In reply to ]

Jul 4, 17 3:26

Post #19 of 26 (3064 views)

Last edited by: Pantelones: Jul 4, 17 3:32

Re: New Quarq does not match P1 Pedals [tetonrider] [ In reply to ]

Jul 4, 17 4:56

Post #20 of 26 (2995 views)

I don't know much about this Quarq, but I do know the PowerTap do not allow a true slope calibration. I suspect that SRM is the only one that allows this. I think PowerTap hubs have done pretty well without allowing the calibration. I am giving PowerTap some credit as I have thought their hubs were very good and assumed the pedals followed suit.

Dimond Bikes Superfan

Re: New Quarq does not match P1 Pedals [ericlambi] [ In reply to ]

Jul 4, 17 5:14

Post #21 of 26 (2976 views)

sorry its not much help for your current issue but I have another question...have you used the Powertap hub and peddles at the same time. I have and while during peddling the hub and peddles are similar give or take the average power can be 10% less for the peddles do you notice this? or indeed how does the average power compare....P1 V quarq

Re: New Quarq does not match P1 Pedals [ericlambi] [ In reply to ]

Jul 4, 17 7:52

Post #22 of 26 (2906 views)

Quarq units allow for a manual slope calibration.

I think the pedals ARE very good, the problem you are running into is in not really being sure of either unit. For what it's worth, I have 2 x Quarq (XX1 and Red) and a set of Vectors and am relatively unsure of any of them (i.e. I have never performed a static calibration). But I also just don't really care.

Re: New Quarq does not match P1 Pedals [ericlambi] [ In reply to ]

Jul 4, 17 8:04

Post #23 of 26 (2893 views)

From the way you noted the intervals, it does sound like drifting. Plotting* the two units over the top of each other can help to sort out the drift piece.

The shift in zero offsets on the P1 from 10 to 5 is drastic. That's big. At that point I'd want to know more about the temp before you started riding, when you zero offset pre-ride, etc... Also, it's not clear to me, was this the first ride after installing them on this crankset? I saw that it sounded like you had them on but swapped. If it's the first ride - did you do some solid sprints (just 2-3) to settle?

Also of course if you configured/checked crank length on the P1. I always like to just ensure it's set to something in the Garmin, for the mere reason that if somehow somewhere else it got set to a wrong value, the Garmin will automatically override it back to reality.

Of course, as others noted you could easily do a static check on the Quarq too, which might help. But I suspect it's the P1 and something was amiss with the offset.

*There's a slew of tools out there to use, Golden Cheetah is free, WKO4 can do it too, Excel for free, or also the DCR Analyzer too. Whatever floats your boat.

-
My tiny little slice of the internets: dcrainmaker.com

Re: New Quarq does not match P1 Pedals [dcrainmaker] [ In reply to ]

Jul 4, 17 12:49

Post #24 of 26 (2805 views)

You are right, I did this test immediately after installing the pedals on the bike. Hadn't remembered that they would need some time to settle. Unfortunately, they still didn't match after the second zeroing. Do you think it's worth repeating with a break-in period for the pedals? If so, what do you recommend to prep the pedals after install?

To the other user that asked about wheel vs pedals ... I haven't tried, I just set the wheel aside after I got the pedals as I didn't have this scenario where I wanted to switch back and fourth.

Dimond Bikes Superfan

Re: New Quarq does not match P1 Pedals [ericlambi] [ In reply to ]

Jul 5, 17 0:41

Post #25 of 26 (2702 views)

So I suspect that explains everything (and thus, this entire thread), especially depending on how tight you had torque'd them.

My procedure is pretty simple to be honest. I tighten them first to a 'normal' feel. I don't know what normal is, but I'm certainly not fighting with the bike having an arm wrestling contest. Then I do a zero offset.

After that, I do approx one loop around the block, which gives me a chance to do 3 sprints of about 5-8 seconds each, usually maxing out around 700w or so. Often I'll backpedal 4-6 times. Then I do another zero offset. I'm not 100% certain the second zero offset or backpedal really does anything in this case (pretty sure it doesn't), but it's a bit of a habit.

I've had pretty good luck with this process...thus, I just kinda leave it as is. You can obviously do this on a trainer instead.

-
My tiny little slice of the internets: dcrainmaker.com

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