Another newbie question about 'zero offset' on Quarq DZero powermeter

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Greenduck
Posts: 235
Joined: Fri Apr 08, 2011 6:36 pm

by Greenduck

Hello,

I just a Quarq DZero powermeter for my bike. I have installed the Qalvin BLE app and have connected to the powermeter.

According to the app the offset is -53. So I press "Set Zero (Calibrate)" and the app tells me that it has passed and the returned value is -52 [-1.625 Nm]. I press OK and the "Offset" says "Loading..." a few seconds and then return to the said value of -52. The bike is standing still with the drive-side pedalarm in 6 o'clock position.

Here's my question: Shouldn't it go to 0 (zero)?

Regards,
Jake
Last edited by Greenduck on Fri Feb 23, 2018 10:44 pm, edited 1 time in total.
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oldturd
Posts: 93
Joined: Thu Oct 06, 2016 12:10 am

by oldturd

i thought so at first as well.. but it doesnt need to be 0

https://quarq.zendesk.com/hc/en-us/arti ... offset-be-

per website:

Quarq Zero Offset Guidlines: The Zero Offset of a Quarq power meter does NOT have to be a certain number, per se. It should instead meet BOTH of the below criteria.

The zero offset value must return within +/-1000.
The zero offset must not drift more than +/-50 points during a single ride.

mine is typically -150ish

hope this helps

Greenduck
Posts: 235
Joined: Fri Apr 08, 2011 6:36 pm

by Greenduck

This definitely helps. Strange I didn't find that on Quarqs website.

Thanks!
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Greenduck
Posts: 235
Joined: Fri Apr 08, 2011 6:36 pm

by Greenduck

Another question:

Today I rode on my bike on the Wahoo Kickr Power, the latest generation. Zwift recorded the power of the the Wahoo Kickr and my Garmin Edge 520 recorded the power from the Quarq. I zeroed the offset before riding and with the bike mounted in the trainer.

The data between the two was pretty consistent, with the Quarq/Garmin showing bit higher watt and higher average. But in the end of my ride I did a short sprint.

The Wahoo Kickr Power/Zwift recorded a max. power output of 955 watt. The Quarq/Garmin recorded a max. power output of less than 500 watt.

Why is there such a big difference? The difference in average power output was around 15 watt.
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TobinHatesYou
Posts: 1200
Joined: Mon Jul 24, 2017 12:02 pm

by TobinHatesYou

Did it feel like 955W or <500W? At least we’d be able to identify which device was in error... For example, last night I did a 1min max effort starting at sprint power. I could only hold 955W for 9-10s, and after a minute my average was 545W. If I wanted to, I could hold 500W without the heavy peak for probably 90s. So what kind of effort was it?

There is no explanation. If the KICKR had a spindown performed after a 10min warm-up and the Quarq was zeroed, then they should be within a few watts. Traditionally KICKRs have calibrated on the high side what whatever reason, but a 15W lower average could be explained by claimed accuracy tolerances and some drivetrain losses.

Greenduck
Posts: 235
Joined: Fri Apr 08, 2011 6:36 pm

by Greenduck

Thank for the reply...

It did feel more like a 900 watt sprint effort. I will do some more tests this weekend and see if the difference continues. I'm not worried about the difference in average power output.
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Calnago
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by Calnago

Do you have the record interval set for 1 second on your Garmin?
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glepore
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by glepore

Another thing-when did you install the chainrings? They'll take a few rides to settle in and become consistent.
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ergott
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by ergott

Should have 1 sec. recording set and your definetion of a sprint should be a couple rotations of the crank. If you are talking about a single stomp on the crank it won't always give you peak reading since it's an average of 1 sec power each data packet. If you are talking about 900W over a couple seconds then something needs sorting.

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jekyll man
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by jekyll man

Dont forget your kickr records what it does to respond to your effort, so they may not match, esp over very short intervals.
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Greenduck
Posts: 235
Joined: Fri Apr 08, 2011 6:36 pm

by Greenduck

Hey guys,

Thanks for all your replies.

My Garmin was set to Smart Recording and so I have changed that to 1 sec. interval. The power was installed a few days ago. I moved the chainrings from my old crankset to the Quarq. It was a 2-3 second sprint. I'm on the Kickr tonight so I will see what the readings are then.
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TobinHatesYou
Posts: 1200
Joined: Mon Jul 24, 2017 12:02 pm

by TobinHatesYou

2s is not a sprint. This probably has nothing to do with smart recording as many power meters can take 1-2s to respond to changes in angular velocity. The Quarq DZero in particular does not poll angular velocity frequently enough to accurately measure power from non-round chainrings for example. The KICKR doesn’t have this problem as it simply relies on optical detection of flywheel acceleration/speed and a brake strength number to calculate your power.

Had you done even a 5s effort, the peaks from each power source would have probably been similar.

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