Comparison of Tacx Bushido vs Powertap SL+

Here’s one for cyclists: A quick comparison of the power measurement from a Tacx Bushido and a PowerTap SL+ hub. The data was acquired over a 10 mile time trial simulated by Tacx Trainer software 2. Data from the PowerTap was recorded with a Garmin 705.

The procedure:

  • Calibrated Bushido with the coast down test. Obtained 10.9
  • 5 minute warm up at ~250 Watts
  • Calibrated Bushido again. Obtained 10.2
  • Calibrated PowerTap via the Garmin 705
  • Road the 10 mile TT (took 20 minutes 49 seconds)

I then wrote a quick Python script to plot the data exported from Tacx Trainer and tcx file from the Garmin. Here are the results:

Some observations:

  • Cadence which is estimated from variations in torque by both devices is only an approximation to the real cadence.
  • Heart rate which in both cases is measured by a Garmin Ant+ monitor is (almost!) the same as would be expected.
  • Average power output from the Bushido is recorded ~6% higher at 372W than the PowerTap which averages 352W.
  • The power output from the Bushido drifts upwards with time, whilst the output from the PowerTap does not. However the output from the PowerTap was used for pacing so it is impossible to determine which one is drifting.
  • The power output from the Bushido is less noisy than that from the PowerTap.
  • Tacx Trainer 2 is easily the worst piece of software i have ever used.
  • The Bushido on the other hand is well engineered, that is apart from the screen on the head unit which is terrible.

In conclusion I was very pleased to see a good agreement between both devices. If the correction factor on the Bushido was adjusted, it could be made to agree closely with the PowerTap. However, most importantly the Bushido measures consistently and is therefore a very useful training device on its own.

I’ll upload the script i wrote when i get a chance.