Calibration of power meters. Different reading on different bikes?

Triathlon Forum
1

I fitted some BB30 adapters to allow my quarq GXP red power meter to be fitted to my road bike.

I noticed that when I calibrate the the PM that the value is different from what it is on the tri bike, and consistently so.

The method I use is to activate the PM be pedalling a few times and then selecting the manual zero option in Trainerroad. On the tri bike, I always seem to get a value of 542 (or very close to it). Onahe road bike. it appears to come in at 396. I have also calibrated using my garmin 810 and got a value of 398 from this.

Not sure if this is something I should even be thinking about and what the different actually means in terms of power measurement.

Thanks

2

That’s really weird. Try calling Quarq? They’re pretty helpful on the phone. Would love to hear what they say.

3

do you have a pattern of bike storage such that the crank would be at a different temperature when zero-ing it on one bike vs the other?

4

Different offset is no big deal.
Has to do with different bb, chain, chain length, chain wear, etc.
If it was the same it would not be accurate.

5

No. They are both stored in the front room and on the same trainer.

Are you expecting them to be similar then?

Thanks

6

How do those things affect the static zero process?

Different offset is no big deal.
Has to do with different bb, chain, chain length, chain wear, etc.
If it was the same it would not be accurate.

7

I am, yes. But I am not an expert on that power meter. I could be wrong.

No. They are both stored in the from room and on the same trainer.

Are you expecting them to be similar then?

Thanks

8

Interesting.

I have some new batteries for the PM that I intend to install tonight. I got a warning on the garmin on the way into work that suggests it at least thinks the battery is low, even though it was only put in a month or so ago. Once I have done that, I will swap them back over and see what the figures say on both.

Perhaps an email to quarq might be in order.

Thanks

9

Seems a bit odd. I swap my Riken between road and TT bike multiple times per week, using the same Garmin 500. The zero offset varies with temperature a total of 25 units. I don’t see any difference bike to bike and don’t expect that I would.

The offset values you have are also pretty large. I think the max offset amount from Quarq is 500 and then you should talk with them.

10

quarq says mine are fine at 540+/- on my red unit. only thing I can think of is bolt tension maybe affecting it, not sure that it would though

11

Put your powermeter on another bike and see.
Zero offset assumes no tension, but tension of chain and bb resistance are still there and not the exact same on two different bikes.
Heck, if you install a new chain on same bike it could change offset numbers.

12

I am, yes. But I am not an expert on that power meter. I could be wrong.

No. They are both stored in the from room and on the same trainer.

Are you expecting them to be similar then?

Thanks

The zero offset number on a Quarq (especially the older ones) can vary depending on the installation, even when swapping from bike to bike. Not an issue as long as it’s stable once installed.

13

I bet he could put his power meter on any bike designed for 130mm old and his zero offset wouldn’t change because of it.