SRAM uses a similar removable spider across their road “S” series cranks and some of their mountain “X” series cranks. I’ve taken off the spider on the mountain cranks, and can’t see an issue doing so for the S975 crank (as its the same exact bolting).
Can anyone imagine a reason this would change the calibration of the quarq if I were to go from 175 to 172.5? As I understand it the quarq’s measurements are determined only by the spider and chainring, thus the arm itself is constant. Is that right?
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.
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.
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.
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.
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.
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.
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
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
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)
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.
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.
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?
Besides, it’s pretty simple and takes nearly no time at all.