I have a left arm sram rival axs left arm crank power meter on my gravel bike? I have do the calibration in in garmin edge before each ride. I had not been facing the drive side crank arm in the 6 o’clock position before doing the calibration. I wonder if that makes a big difference. I either didn’t realize it was supposed to be in that position or just forgot over time.
Most of my outdoor rides, especially when not training for any event, are mostly just endurance stuff where I am not paying too much attention to power and riding by feel. But I’ve had a few rides where I’ve ridden pretty hard either in a race or just with some friends and have been surprised on the lower PM numbers based on how I felt during the ride and also what my HR readings were.
Would not calibrating with the crank arm in that 6 o’clock position make that much difference in PM readings?
I have a kickr bike at home so can’t throw the crank arm on there for comparison.
I know both dcrainmaker and gplama had posts long ago about low readings for the sram crank arm PMs but I have not seen much else referencing issues.
I’ve had my eye on the assioma pro-mx pedals anyway since I would like power on my mountain bike so at that put I could do a real comparison.
The reason to put the crank vertical for calibration is so that the weight of the arm and pedal are not contributing a torque when the strain gauges are zeroed. I haven’t thought about it or tried to calculate the effect so IDK how big an effect it is. I won’t be huge.
FWIW: Power is torque times angular velocity. Torque is the component of force perpendicular to the crank arm times the crank arm’s length. With the crank arms vertical, the weight of the arm and pedal act parallel to the arm so contribute no torque.
At the beginning of your ride . Yes. It gets rid of any temp accumulation correction built into your power meter from previous rides.
“”” Active Temperature Compensation
Power meters with this technology adjust for changes in temperature during your ride, leaving you free to focus on the churning out the watts. Roughly two-thirds of power meters actively compensate for temperature drift. “””
If the temperature is fairly constant, I’ll go for weeks at a time without calibrating my Stages. My calibration always comes back on the mark (~905) when using good batteries.
For those with Stages, I found that name brand retail batteries made a huge difference in power reporting reliability. Those cheapo 10 and 20 packs you find on Amazon were a no go. Even oem packs of Energizers off Amazon were bad - maybe fake?
I’ve had the best of luck with full retail Duracell, Energizer, and Panasonic CR3032s lately. (You can still buy them on Amazon if you want.)
The retail pack batteries also last 2-3X as long as the cheap 20 pack batteries so the actual cost per ride is minimal and inconsequential.
Well zero offset is what is doing thst, bit like zeroing scales before weighing anything. Certainly 4iii don’t do it automatically, you have to zero offset.
Yeah I found the same thing, though with Sony batteries from Amazon, they were expiring very quickly, after a few weeks in some cases, thus I assume they were fakes. Using Duracells now, lasting much longer
I’ve wondered if this is why Stages often got a bad rep over the years. I mean, doesn’t everybody buy multipacks on Amazon? My Stages has been rock solid reliable and consistent since figuring this out. (Sadly, I struggled off and on for two years before I figured it out. Stages support never suggested this.)
They clearly require more consistent voltage than other devices. I’ve never found any other device that didn’t work with cheap batteries.
