Tuesday, 20 May 2008

PowerTap vs CompuTrainer Comparison - 2x20 SST Session @ "265W"


The graph below shows the data from tonight's session as recorded on my CompuTrainer (Lab Pro 3D version) and the loan PowerTap. Important points to note are as follows:
  1. Continental trainer tyre inflated to 110psi.
  2. CompuTrainer warmed up for 10 minutes at 175W prior to calibration.
  3. CompuTrainer calibrated after warmup, calibration reading (press on force) 2.37.
  4. CompuTrainer calibration rechecked after session, calibration reading 2.35 (effectively no drift).
  5. All power (load) settings controlled by CompuTrainer .erg file, no user interference or adjustment.
So, 2x20 minute efforts in ergometer mode at a nominal 265W were performed.

Here are the results:

It can be seen that the PowerTap readings were consistently lower, the overall (whole session) averages for the session recorded were CompuTrainer 233W, PowerTap 224W. The average figures for effort 1 were CompuTrainer 265W, PowerTap 257W and for effort 2 CompuTrainer 264W, PowerTap 258W.

So, there was a difference, who knows which figures are "right". If I assume that the ergo function on the CompuTrainer keeps the load steady there did seem to be more minute by minute fluctuation in the PowerTap readings but that's a bit subjective.

Any thoughts on the matter welcomed!

1 comment:

  1. 6/258, it's a 2.3% difference...The Powertat reads the power on hub, is the computrainer reading on cranks? The strictions and chain works could explain this small gap.
    Thanks for your expi!

    a french blogger