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2014-01-16 6:12 PM

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Subject: Power meter question?
So I got a second hand bike that has a Quarq power meter and I was trying to change the chain rings to put on a set of Q rings. I was not able to remove the smaller round chain ring over the power meter device to install the Q rings. Does anyone know the correct process to do this? I was concerned about doing something that would mess up the power meter's calibration. Also, can I change the crank arms on the power meter? I'm new to power meters and I haven't figured out the do's and dont's yet. Thanks!

Edited by Tri-a-betic 2014-01-16 6:19 PM


2014-01-16 7:33 PM
in reply to: Tri-a-betic

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Subject: RE: Power meter question?

The older quarqs require (or at least highly recommend) you send in the crank and have them replace the chainrings.  It has to do with the calibration of the unit.  Even if you were successful in swapping out the chainrings, the power it spits out may be unreliable unless you are familiar with the calibration process.  I think the Qalvin app (for iphone/ipad) in conjunction with an ANT+ sensor can be used, but that's beyond my expertise.

I would highly suggest you call Quarq (they have excellent customer service) and ask them how to proceed.  The fact that you removed the outer chainrings means you have some careful work to do even if you want to put the ring back on and have it work properly.  I think it's just a matter of properly tightening down the bolts.

The newer Quarq cranks (Riken and Elsa versions) do not rely on the chainrings to measure power, so you can change those rings without re-calibration.

I'm not sure if it's possible to swap the crank arms.  My first thought is no...but I don't know for sure.

2014-01-17 6:14 AM
in reply to: Tri-a-betic

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Subject: RE: Power meter question?
Is this a compact crank set? Two things, you need a OCP3 outside ring, the standard Q-rings do not fit Quarq's. Second, you will more than likely have to remove the crank set to install the inside ring. I have a Rotor 3D with Quarq and Q-rings and it's really a tight fit trying to fit the small ring over the crank and install it that way. It's a couple of minutes to remove the crank, so that saves a lot of aggravation.

And as mentioned, Quarq do calibrate the power meters according to round or Q-rings… it will through off the data, but not by that much and it doesn't change consistency of the information (i.e you may be off a few %, but you are ALWAYS off the same %)
2014-01-17 7:29 AM
in reply to: Tri-a-betic

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Subject: RE: Power meter question?

1. Send your Quarq back to them to have it re-calibrated once you get the chainring thing figured out.  Their customer service is top notch and they will send it back almost as soon as they get it.  There is a way to re-calibrate it yourself but it may be cost prohibitive unless you already have an ANT+ dongle to fit into your smart phone and an accurately measured weight.  See this page for self-calibration: http://www.quarq.com/qalvin

2. My understanding is that you can change crank arms if the crank arms are the same make and model and the switch is to change lengths or replace a broken crank arm.  Changing to completely different cranks isn't going to work as the Quarq is attached to a crank specific spider.  That's my understanding.

2014-01-17 10:46 AM
in reply to: GMAN 19030

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Subject: RE: Power meter question?
They are not compact cranks. They are 175 in length and I was thinking about changing them to 172.5. The size of the Q rings is a standard 130 and will fit on the Quarq. Does anyone have a reference on how to remove cranks to install rings? Once the cranks are off and the rings are put on then I should send it to Quarq to be calibrated? Another thing is I'm not sure of the rings settings yet. So once it's calibrated I shouldn't mess with the bolts and reposition the ring settings? I usually spin about 85rpms and I find the #3 Q rings setting the best right now on my tri bike. But if I put them on the 175 crank arms I may have to change the ring settings
2014-01-17 11:03 AM
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Subject: RE: Power meter question?

Originally posted by Tri-a-betic They are not compact cranks. They are 175 in length and I was thinking about changing them to 172.5. 

"Compact" when speaking of cranks is in regard to the chainrings, not the length of the crank arms.  Standard cranks are usually 53/39......compact cranks are 50/34. (number of teeth)

Here ya go:

 

http://www.stevehoggbikefitting.com/cycling/2011/05/compact-cranks-vs-standard-cranks-gearing-implications/

 



Edited by Left Brain 2014-01-17 11:05 AM


2014-01-17 12:33 PM
in reply to: Left Brain

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Subject: RE: Power meter question?
So do they make 175 length arms on a size 110 BCD chain ring or can you use 160 cranks on 130 BCD 50/34 chain rings? It seems they go hand in hand. Shorter cranks use smaller rings. Mine are 53/39 and use 130 BCD rings. I'm looking at changing 175 to 172.5 both 130 rings and I am wonder if this is possible with Quarq and its calibrations. But I also hear riding longer crank arms isn't bad with q rings because they guide you out of that 12 o'clock position and then the length gives you more leverage for power on the down stroke.
2014-01-17 12:46 PM
in reply to: Tri-a-betic

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Subject: RE: Power meter question?

There is not a correlation of shorter crank arms to smaller rings. There is just what manufactures believe people will by using the standard and compact BCD. There is no reason any crank arm size can't be available in either size BCD. What you are looking to do (as best I can tell?) seems kind of complicated because of the powermeter being built into the crank set. Generally one would sell the whole thing and get the size crank & BCD they wanted. The chainrings do have some limitations as to what will fit, but there are some options for each BCD size.

2014-01-18 9:17 AM
in reply to: Tri-a-betic

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Subject: RE: Power meter question?
Crank arm length is directly related to your bike fit, has nothing to do with your gearing.

The compact (110 BCD) allows you use to use 50/34 (most common), 50/36 (allows for a slightly less of a gap between the chain rings, which may improve shifting and be more comfortable to ride unless it's REALLY hilly around you) or 52/36 (also called mid-compact). Standard, 130 BCD), is usually 53/39, but sometimes you will see 55/42 or even 56/44 (rare, but sometimes used on 650c bikes).

You're not going to see much of a different between 175 or 172.5mm cranks, so safe your money. Plus, not all cranks are available with replacement arms, so if may very well mean a new crank set (and even if they are available, it might be just as cost effective to buy a new crank…)
2014-01-20 7:40 AM
in reply to: audiojan

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Subject: RE: Power meter question?

I called Quarq and they said changing a 53/39 round chainring to a 53/39 asymmetric q ring with only have a difference of 0.6 slope. So It would not need to be recalibrated. Which he said isnt a big enough change in slope. But make sure to tighted the bolts to 10nm if steel bolts and 8nm if aluminum. The power meter I own was discontinued in 2010 and it is not capable of having the cranks changed. The cranks will need to be removed to put on the Q rings which he said can be easy but Im thinking about letting my bike shop take care of that.

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