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Quarq D-Zero calibration/accuracy
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So I'm really starting to question the precision of my D-Zero. The calibration number jumps around a bit, usually between 40-50. Is that too big of a range?

If it was just that I wouldn't think much of it, but after racing Sunday I'm really not sure.

In the race on Sunday I avg 25.2 mph on 229ap/232np. (the swim was rough and my HR was sky high at the beginning of the ride and I thought that's why I was having trouble hitting target power)

In a simulation ride a week before (38 miles on the race course in the same weather conditions - 20mph side winds) I averaged 24.8 on 250ap/253np.

Yes, I made a few small changes listed below from the practice ride to the race ride, but nothing that seems drastic enough to avg almost .5mph faster on 20w less.

Swapped 23 4000s to 23 TT tires
Swapped from regular hed skewers to view-speed skewers
Swapped from Jet+ 9 in front to Jet+ 6 for the crosswinds (figured this would have made me slower?)
Moved my garmin from on top of my BTA bottle (xlab kompact) to in between my extensions up by my hands to get it out of the wind
Put on a brand new freshly waxed chain (broke it in for 30min day before)
Swapped to single behind the seat bottle holder from double
Did not wear my 920xt until the run

Can all of those little things really add up to that much difference? The effort felt the same, that's for sure. And my legs felt much worse coming off the bike during the race than any of the tempo bricks I did before, even a 50 miler at 250w.
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Re: Quarq D-Zero calibration/accuracy [Sean H] [ In reply to ]
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Did you zero the Quarq in transition with it at the ambient temperature? The temp cal on them is good, but better when zero'd consistently. In general Quarqs are pretty damn good.

Also, were the weather conditions really the same? A 1mph difference in wind speed, or a different direction will have quite an impact.

Developing aero, fit and other fun stuff at Red is Faster
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Re: Quarq D-Zero calibration/accuracy [Sean H] [ In reply to ]
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Sean H wrote:
So I'm really starting to question the precision of my D-Zero. The calibration number jumps around a bit, usually between 40-50. Is that too big of a range?

If it was just that I wouldn't think much of it, but after racing Sunday I'm really not sure.

In the race on Sunday I avg 25.2 mph on 229ap/232np. (the swim was rough and my HR was sky high at the beginning of the ride and I thought that's why I was having trouble hitting target power)

In a simulation ride a week before (38 miles on the race course in the same weather conditions - 20mph side winds) I averaged 24.8 on 250ap/253np.

Yes, I made a few small changes listed below from the practice ride to the race ride, but nothing that seems drastic enough to avg almost .5mph faster on 20w less.

Swapped 23 4000s to 23 TT tires
Swapped from regular hed skewers to view-speed skewers
Swapped from Jet+ 9 in front to Jet+ 6 for the crosswinds (figured this would have made me slower?)
Moved my garmin from on top of my BTA bottle (xlab kompact) to in between my extensions up by my hands to get it out of the wind
Put on a brand new freshly waxed chain (broke it in for 30min day before)
Swapped to single behind the seat bottle holder from double
Did not wear my 920xt until the run

Can all of those little things really add up to that much difference? The effort felt the same, that's for sure. And my legs felt much worse coming off the bike during the race than any of the tempo bricks I did before, even a 50 miler at 250w.

To answer the first question, an zero-offset range on a Garmin of 40-50 is extremely normal.

Garmin calls this calibration, but it's really the zero-offset in 1/32*Nm increments. Basically, a zero offset of 40=40/32=1.25Nm of offset on the y=mx+b power equation, where zero-offset = b. 50=1.5625Nm. Assuming a cadence of 80rpm, that'd result in a power difference of 0.4w between those two values.

"Non est ad astra mollis e terris via." - Seneca | rappstar.com | FB - Rappstar Racing | IG - @jordanrapp
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Re: Quarq D-Zero calibration/accuracy [Sean H] [ In reply to ]
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Sean H wrote:
(the swim was rough and my HR was sky high at the beginning of the ride and I thought that's why I was having trouble hitting target power)


A hard swim can really hurt your bike; a lot. Your high HR is a sign you put a lot of energy into the swim. Plus, you cannot compare different days when you ride the full course one day, and only part of the course the other; and you don't account for wind on the entire ride. (You did not mention the course, but if this course has any notable hills, that alone will have a huge affect.) This is just one reason why I think people over-rate the value of power meters for racing. The power target you think you should race at may well be wrong on race day for a variety of reason, including over-swimming.

And yes, a range of 10 on the Dzero is normal based on my usage; especially since you put on a new chain. (My understanding is that the zero offset values will slowly change with drivetrain wear. Replacing the chain is thus changing that characteristic.)

2015 USAT Long Course National Champion (M50-54)
Last edited by: Paul Dunn: Apr 4, 17 13:26
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Re: Quarq D-Zero calibration/accuracy [Sean H] [ In reply to ]
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Congrats! You had a great race.

Did your tire swap include changing from butyl to latex tubes? This plus the GP4k to SS swap could be nearly half of the 20 watt difference. Your other changes help. The rest could be weather and the difference between holding aero while racing vs maybe less concentration for training.

The post above about swimming could easily explain the RPE difference you felt. I am a strong cyclist and weaker swimmer and it always amazes me how much it pulls down my bike power.
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Re: Quarq D-Zero calibration/accuracy [SkippyKitten] [ In reply to ]
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Thanks for all of the replies, this has me feeling good about the quarq.

Yes, I always zero the quarq prior to a ride. That's the number that I'm referencing jumping around.

You have a point, it probably wasn't exactly the same but pretty damn close. This was Galveston, so a straight out & back and both rides my speed in both directions was very similar, and both slightly slower on the way back.
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Re: Quarq D-Zero calibration/accuracy [Rappstar] [ In reply to ]
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This was my main question. Thanks for the thorough explanation. I'm a 90 rpm guy but still doesn't look like this calibration (zero) number should be of concern.
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Re: Quarq D-Zero calibration/accuracy [Paul Dunn] [ In reply to ]
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Yes, you're absolutely right, and I've experienced it before. My plan was to swim easy so I could hit target power right away. But when we start the swim almost directly into 20mph winds and every yahoo in my AG thinks he's Michael Phelps, well my plan got destroyed. It was a washing machine. Big gulps of seawater swallowed. Then I guess since the swim was hard on everyone the whole course in front of me was crowded the entire way. I couldn't get into an easy rhythm. I need to work on that for sure. I don't really like the idea of sprinting out in front of my AG, but that might be best then settle down into an easy effort.

As to your second point, I'm not sure I follow how that could be true. Isn't the quarq just a strain gauge? How could a different chain with the cranks under zero load change the calibration (zero) value?
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Re: Quarq D-Zero calibration/accuracy [SummitAK] [ In reply to ]
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Thanks!!!

Nope, latex on both rides. I held aero the whole way on the practice ride but you mentioning that did remind me that I had to stop at 2 lights on that ride so that definitely could have had a big impact that I somehow overlooked.

Agree, as mentioned I've got to figure out how to hit the bike in better shape. I guess I may have to swim more. I don't swim that much and put out competitive times, but I obviously hadn't swam enough to bike as hard as I had been when not swimming before.
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Re: Quarq D-Zero calibration/accuracy [Sean H] [ In reply to ]
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You say it was the same weather conditions... can you look back on the historical weather archives and see if the air density was the same?
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Re: Quarq D-Zero calibration/accuracy [nickwhite] [ In reply to ]
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Good idea. Here's the data.

Race day:
Time Temp DewPt Hum Press Vis Wind
8:02 AM 75.9 °F 73.0 °F 91% 29.77 in 9.0 mi SE19.6 mph
8:52 AM 77.0 °F 73.0 °F 88% 29.75 in 4.0 mi SE21.9 mph
9:33 AM 77.0 °F 73.0 °F 88% 29.74 in 5.0 mi SE19.6 mph
9:52 AM 78.1 °F 73.0 °F 84% 29.74 in 5.0 mi SE20.7 mph
0:49 AM 78.8 °F 73.4 °F 83% 29.75 in 2.5 mi SE20.7 mph


Training day:

8:52 AM 73.0 °F 68.0 °F 84% 30.02 in 8.0 mi SSE17.3 mph
9:52 AM 73.9 °F 68.0 °F 82% 30.05 in 8.0 mi SSE15.0 mph
10:52 AM 75.9 °F 68.0 °F 76% 30.07 in 8.0 mi SE19.6 mph
11:52 AM 77.0 °F 69.1 °F 76% 30.05 in 10.0 mi SE20.7 mph
Last edited by: Sean H: Apr 4, 17 12:54
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Re: Quarq D-Zero calibration/accuracy [Sean H] [ In reply to ]
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You did get considerably different wind on race day. How close to other riders did you ride? Did you slingshot any? (Implying "legal draft" here).
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Re: Quarq D-Zero calibration/accuracy [nickwhite] [ In reply to ]
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On the way out I must have passed a thousand people, it was nearly continuous. But I was passing them on the left and the wind was coming from the left.

On the way back I barely passed anyone compared to the way out but not sure exactly how many. I was all alone for long stretches.
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