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STAC ZERO: Calibration

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Spin down calibration fails 

STAC Zero trainers do not require a spin down calibration. Look for the option to skip this step. To learn why, see this article. 

Is there a calibration procedure? 

The STAC Zero Halcyon and Powermeter come calibrated for a 700c road wheel or 29" MTB wheel. If you have a different wheel size update the wheel rim circumference value using the STAC Control Panel app.

Where can I update my Brake Rim Circumference? 

  • Download STAC Control Panel from Play Store or App Store.
  • Open the app and connect to your STAC Zero Halcyon or Powermeter.
  • Select "Settings and Firmware"
  • Update the value in "Brake Rim Circumference (mm)" and press send.  

What does the default value "1951" mean? How do I know what value I should use?

1951 is the default value for a 700c (or 29" MTB) wheels.  How did we get there?

  • The diameter of a 700c wheel (ISO number) is 622 mm.
  • We subtracted 1 mm because the magnet arrays did not face the outermost edge of the rim on the 700c wheel we used for this initial calculation. 
  • Multiply the diameter by pi to find the circumference. 
    pi*621 =1951. 

This Wikipedia article has a list of wheel sizes with their ISO numbers: To make your own calculation for a different wheel size, use:

(D-1)*pi

If, like in our example, the magnet array is just inside and the edge of the brake rim, and

D*pi

if the bottom edge of your magnet array line up with the edge of the brake rim. 

Can I calibrate the STAC Zero Powermeter or Halcyon to exactly match another Powermeter?

To match two difference power readings: 

  1. Do a short ride, recording the power readings from both devices.
  2. Take the average reading of both devices.  
  3. Divide the trainer's average power by the powermeter's average power. 
  4. Open the STAC Control Panel app on you phone, and connect to your trainer.
  5. Select "settings and firmware".
  6. Multiply the default value in the "mV perV" field by the result of your first calculation.
  7. Enter this new number in "mV perV" field.
  8. Select "Send."

In other words: newMilliVoltsPerVolt = (TrainerAverage / PowermeterAverage) * oldMilliVoltsPerVolt

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