The crank length is an important factor in the power calculation. The Quarq measures rpm and torque. Torque depends upon the length of the crank and the weight/force applied to the pedal.

So no you can't just swap crank arm lengths without going through a calibration.

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Suffer Well.

AH! Thats right! How could I have forgotten?

Pwr = Tq x Spd

thanks.

FWIW, I called SRM about doing the same thing (actually went from 175 to 170) and they said not to worry about it, that any difference would be so minor it would not show up.

Actually, that's not quite true. Since the Quarq already is measuring the torque, then the length of the crankarm applying the torque makes no difference in the calibration. Torque is torque. Theoretically, one should only need to perform a zero offset reset after swapping the spider onto a different crankarm (to compensate for any zero bias changes).

That said, if I was to swap the crankarms on a Quarq I'd STILL put it through a calibration using Qalvin just to make sure nothing has changed. But then, perhaps that's just me being OCD ;-) Besides, it's pretty simple and takes nearly no time at all.

Oh yeah...you would have to change the crankarm length value in Qalvin when this is done...but, that's just to tell the program what actual torque is being applied for the given weight being hung.

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http://bikeblather.blogspot.com/

What are people using for the reference weight for calibration? I would prefer to find an alternative to the expensive reference weight
listed on the quarq site.

You can use anything you want, as long as you have it weighed on a calibrated scale (post office, shipping, etc.)

For example, I actually use a bag of truck tire chains :-)

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http://bikeblather.blogspot.com/

Hi, I also need to change the spider on a quarq riken crankset, but I would like some advice on how to do it.

Since in this thread I see some users who have done it, maybe you could help?

I tried removing the bolts but the spider did not come off.

Should the spider come loose just by removing the bolts or is it necessary to use some tool or some amount of force to remove it? Is it pressed in?

Thanks for any help, I do not want to sent them all the way to the USA just to have this done.

Have a nice day!

There is likely some low strength loctite between the spider and arms. A slight tap is all it should need. I just completed the process and that is all it needed for me

Zach, what model Q were you using and what model/length of crankarms do you install ? Instructions were exact ?

I have a quarq elsa bb30. Used force 22 arms to swap from 175 to 165. I bought a new force 22 crank and just swapped the arms on the two cranks.

This can also be done with s900 series crank arms.

You can also go from bb30 to gxp and vise versa this way.

Instructions are easy.

Clean all residual loctite compound from spider.
Prep surfaces by wiping down
put one drop of loctite 242 in each threaded hole
put one drop of loctite 680 on the other 7 "tabs" between where the two pieces mate.
Install and tighten the three torx screws to 10 nm and let cure for 24 hours.

Done.

Just buy the smallest bottles of loctite (0.5ml) I'd you don't have it already. I got the loctite for around 18 bucks shipped to my door (shipping was most of that)

thanks

did the offset numbers from calibration change much ?

Not that I noticed. I had notification from quarq that calibration was not required post swap

Most useful post ever award goes to Zach. Now I'm looking for a 165mm Force 22 set...

I agree, useful to the max!! Thanks very much, I'll give it a try and come back to you guys to inform how the process goes.

Thank you Zach!!

Tailwinds

Alfredo

EDIT: I completed the process with success apparently, yet to take the cranks for a ride, but for crank number 1: Torque Raw before: 0, after: 0; Torque offset before: 0, after: 0. Crank number 2: Torque raw before: 0, after 0, Torque offset before 100 (not 100% sure), after 125. I did have to remove some loctite residue to be able to mount the spiders back and re-loctited them before tightening.

FOLLOW UP: As I was going from 172.5 to 175mm cranks this seemed to mess up the calibration and high power numbers were showing during my next ride. A quick recalibration with Qalvin solved the problem. Slope was changed from 9.09 to 9.02 if I remember correctly.

Zach, sorry to revive old thread with a potentially stupid question. If I was picking up a crankset purely for the crank arms to put them on my Quarq, would the BCD matter at all? I can't see why it would matter if I wanted to put arms from a compact, for example, on my 53/39 Quarq.

Also, when you say that you can go from BB30 to GXP this way, is that because when you disassemble it the spindle is a part of the crank arm? On my BB30 Quarq the spindle is part of the (edit) non-DS assembly.

Hope that makes sense, and thanks for help.

Bcd does not matter. You will remove the spider anyways.

the spider does not have different interface for bb30 or gxp. So if you have bb30 now you can remove those arms aND replace with gxp arms no problem.

Thanks Zach, appreciate it. My Quarq is 53/39 BB30 in a BSA frame with adaptors. If I'm going to put shorter crank arms on there I'd quite like to go native BSA with a GXP BB, and I've seen some good options on compact cranksets to that might be the way forward. I think I read somewhere that the Rival 22 also has removable crank arms, although obviously not carbon. Might look at that vs Force which are much more spendy.

Cheers again,
Rich.

Just did the swap thanks to this thread! 165 Force 22's fit like a glove on the Quarq Red.
Too bad the quarq is 130bdc. Can't have everything I guess...

I found this thread via a google search, I was wondering, does anyone have any pro tips on how to first remove the crankarms from the spider? Ive removed the three torx bolts but I'm guessing the loctite is doing its job, the arm is stuck in there really good. This is an unused crankset btw. I guess the obvious solution is to tap it gently with a rubber mallet? If so I'll prob bring it to my LBS, let them figure that out, but maybe there are some easy less cringeworthy home grown alternatives? Any way to dissolve the loctite thats probably causing the arm to be stuck?

Nevermind, I grew a pair and gently tapped it with a small rubber hammer. Problem wasn't gunked loctite as far as I can see, its just that the arm doesnt really want to come out straight, and with the splines I had to tap it slightly from different angles to force it out straight.

Hi,

Old thread revival.

I've got a quarq riken and have just bought some SRAM Rival cranks and had them shortened to 150mm.

I've now had the sudden fear about calibrating the power meter to this length, given that the Qalvin app no longer appears active?

I've seen the legacy version of the app but it's a bit of a nightmare as I don't have a PC!

Do I need to change the crank length or will it be ok?! Can you even change the crank length that short?

It's not been used much in the last 5 years.

Spider-based powermeters don’t use/need crank length as they use strain gauges at a set distance to determine torque then use cadence for calculating power.

Perfect, thanks for the reply.

Did you swap the crankarms or did SRAM do it?