SB20 Power Meters - Zero Reset
What is a Zero Reset?
The Stages SB20 bike has power meters that support a zero reset function.
Zero Reset tells the vertically positioned crank power meters: "Torque should now be zero Newton-meters (Nm)". This allows subsequent readings to be made from a correct offset value. It's like setting 0 lbs/kg on a bathroom or kitchen scale.
Here are things that commonly affect the offset value:
1. Different pedals.
2. Temperature or humidity changes.
3. Nearly depleted batteries.
The Left and Right numbers you see in the Stages Cycling app are an internal representation of the amount of torque that will be added or subtracted from each PM reading.
Before Every Ride?
Should you do a Zero Reset before every ride? It depends. If your riding environment has consistent temperature and humidity then Zero Reset does nothing. If temperature and humidity changes significantly between riding sessions, Zero Reset may be needed.
How do I know if a Zero Reset was needed?
If the offsets shown for Left and Right are within -/+ 1 after successive Zero Resets, then no internal changes were made and the Zero Reset did nothing.
Write down your left and right values. Compare next time you do a Zero Reset.
🔬A change of -/+ 1 is insignificant and should be considered as an unnecessary Zero Reset.
FWIW: My Left and Right numbers don't change very often. I regularly measure my cranks with a Torque Test. It shows that Zero Reset is not needed most of the time in my environment. Result: I do a Zero Reset after changing batteries and then once every couple of months.
Zero Reset is not Calibration!
A zero reset does not "calibrate" the power meter's primary function: measurement of force as you push the pedals. Sometimes called "slope adjustment", a true calibration affects power measurement from low to high efforts.
Much of the confusion comes from vendors like Garmin who incorrectly label their Zero Reset function as "Calibration".
Who can do a Complete Calibration?
Only Stages can do a complete power meter calibration. They limit access to the required software that does a full calibration. Why the restriction? Unscrupulous riders could cheat and calibrate their power meters to inflate power readings. For this reason, true calibration is normally done at the factory in a controlled environment.
Can I do some Calibration on my own?
Yes. You can increase or decrease your overall power readings by -/+ 5% by changing declared crank length.
Here are two ways to do it:
What is "Auto Zero Reset"?
Stages PMs will attempt to do a Zero Reset when the cranks are at rest. They measure crank angle (deviation from vertical) and then do a best effort approximation of the expected reading for vertical cranks.
If you want "Auto Zero Reset" to be more accurate, leave your bike with cranks in the vertical position. But as mentioned previously, Zero Reset is not needed very often when your riding environment has consistent temperature and humidity.
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