Experiencing a strange issue with my PM and wondering if anyone else has seen the same.
I zero offset my PM before every ride. The value given is always between 95 and 105.
I changed my chainring the other day and now my zero offset number is anywhere between 24 and -4. I tried this about 6 times. I then went for a ride and the power numbers didnt seem like a million miles away, but im not that good at riding by feel so it could be misreading as a result of such a different zero offset value.
Any thoughts? Could changing the chainring or torquing the chainset have any affect here?
It’s definitely important to torque down all the bolts properly. A secure (and clean) fit is very important. I believe it’s expected that the offset will change if you change out the chainring, or really anything with the pedals/cranks, because that affects the weight distribution and needs to be reflected in the sensor. With a range of -4-24, that suggests to me there’s still quite a bit of play (could also be the bike wasn’t stable).
Thanks. I used a torque wrench and recommended torque for refitting the chainset. Pretty sure I did that when I fitted it last time. Note that the bolts that attach the PM to the crank arm havent been touched.
Where would you suggest the play is? Theres no play in the BB, as there shouldnt, given that I tightened it to recommended torque. The bike was stable whilst zeroing and was done in the exact same manner as Ive always done it.
The biggest difference between now and then is the size of the chainring, and i can understand this affecting the offset, but it seems like a big change.
Did you take the cranks out of the bottom bracket, or just install the chainring directly onto the bike? Even just pulling the cranks out of the frame and reinstalling can cause offset to change. Also, I’m guessing a new chain, so the weight/tension there is different as well… I don’t usually recalibrate for chains-only changes.
I should probably walk back my “quite a bit of play” comment… that’s the thing with this stuff is you can’t really feel it, but the sensors are very sensitive, so I don’t mean you can feel a wiggle. My cx bike is currently running a 36t on a dzero, and I need to get off my butt and install the 46t now for roadie stuff. Perhaps I can share my experience later today.
Changing your chainring will essentially reset the zero offsets that you are used to. Torque to spec, ride it for a few days with a few sprints, and then monitor the offset. As long as you are floating within a +/-50 range of a stable value, you are good.
I thought the changing rings/torque bolt problem went away with the Dzero series. It was an issue with Riken/Elsa and the older units with a CR2450 battery.
Ok, tore apart my crankset to change from a smaller (elliptical) chainring to a larger circular. Unbolted everything (dzero spider included), cleaned, greased and locktite’d as appropriate. “New” chain… waxed… has some more links than the collection I used for the smaller chainring. I then did a quick spin around the neighborhood to make sure everything was happy. Quarq app shows offset went down slight – from 585 to 541**. I repeated the offset calibration multiple times and it was always +/- 4. At rest, the torque reading would cycle between 0.00 and 0.18 Nm or so. Very slight pressure on the crank would increase the torque, as expected, but no way to validate the accuracy. What I should do is get the tacx neo thru-axle adapter so I can get a comparison, but I’m less convinced that’s $50 well spent.
** Yes, the number is a bit high… went wonky when I bricked a small log jump in a race over a year ago. Doh! but it’s been very stable at this higher offset and feels about right. What little I’ve seen said up to 500 is fine, even under 1000 is probably fine. Outside that, definitely something wrong. Maybe I should ring up sram about it, but seems fine. I’d rather not worry about it unless someone at sram is reading this and wants to send me a new one!
Thanks for this. My offset value is given through my wahoo bolt, ive never used the quarq app. I could give it a go but since I didnt use it before the chainring change, I probably wouldnt learn anything. I guess i’ll just monitor it, try some of my favourite TR workouts and see how they feel
Yeah, I think that’s the article I’m remembering. It’s a lot of words and stuff to basically say “as long as it’s stable, don’t worry about it”. For some reason I had the impression it was +/-1000 for the good-range, but I guess it’s 1500.