Cast for two

Sunday, December 11, 2016

Adding virtual power to your Tacx T2600 workout using Python

In previous post 'Adding virtual power to tcx for Tacx' I talked about adding virtual power to your trainer workout. Today I made a Github repository with a Python program for doing that: vpower

What is needed to be able to add power ? First, you must record your speed during the workout. The power is specifically for the Tacx Blue Motion T2600. This model is not for sale anymore, but the Tacx Blue Motion 2650 is:

The lever for the manual resistance control must remain on the same position during the workout. I leave mine in position 5 and use my gears to alter the workload during the workout.

I use my Garmin 810 for recording but any cycling computer will work probably as well. The result from my Garmin 810 is a FIT file that I normally submit to Strava. If you want to add virtual power, you must do following steps before submitting to Strava:

  1. Obtain a TCX file with speed during the workout: In case of a Garmin, I convert the FIT file of my workout to TCX (I use Garmin Training Center for that, but unfortunately Garmin does not offer it anymore for download).
  2. Process the TCX file with the program from the vpower repository. The result is an altered TCX file with power included. The added power element are derived from the speed you were riding at a certain moment during your workout. It is assumed that you did not altered the lever for the manual resistance control during the workout. Since the lever of the Tacx T2600 is purely mechanical, it can not be recorded by your cycling computer during the workout.
  3. Upload the altered TCX file to Strava.

Why do I use TCX and not GPX? GPX has no extensions for power at this moment.

The linear formula to determine power from speed is based on following drawing:
Suppose that your lever for manual resistance control is at position 5 and your riding at 30km/h, your power is then a little less then 250 Watt.