Following on from my comparison between the PowerTap and an uncalibrated CompuTrainer yesterday I have now taken my tests a step further. Today's test was run having firstly calibrated my CompuTrainer properly according to the instructions using an adequate press on force and a proper trainer tyre inflated to 110psi and cleaned with isopropyl alcohol to avoid tyre slip.
The weather here in Northumberland in the UK was poor so, confined indoors, I rode a route on the trainer that I had previously prepared from GPS data and converted to a 3D course. The route is just short of 50 miles and at a steady pace I would be riding for a bit over 2 hours. The plan was to record the ride on both the PowerTap and the CompuTrainer and compare the data sets.
I was pleased with the results which showed what I had hoped, that is that the 2 units were very comparable in terms of data output. There were of course differences but these are almost certainly a function of the different ways in which the units operate and calculate power. I cannot of course be certain which of the units is "right" but that was not the purpose, the purpose was to find out whether the outputs were comparable.
The main observations I made were as follows:
1). The average and normalised power figures obtained from the 2 power meters were pretty much identical, as were the TSS and IF figures calculated. Looking at the overview graph below it is clear that the overall power figures are very similar for this 2+ hour ride, calibration makes a difference!
2). Looking more closely at the data above and for a 5 minute period (below) it can be seen that the PowerTap records a higher value when there is a short, hard, immediate change in power output, as might be the case in a sprint or other sudden power burst. The result of this is that the PowerTap records a higher maximum power for the ride, at 616W compared to the 565W recorded by the CompuTrainer. The following graph shows the recorded outputs during a 5 minute period including one sudden power output change.
3). I observed that during periods where the "speed" was high, riding in a high gear with a lower cadence the CompuTrainer recorded a slightly but consistently lower power figure than the PowerTap.
A summary of the comparative data as extracted by the TrainingPeaks WKO+ package is enclosed below which shows the remarkable consistency of the figures produced by the units. On the basis of the trials so far I have no hesitation in recommending this combination of equipment for indoor and outdoor training. Having spent a lot of money on this setup I'm happy with the data coming out, even though I'd like the numbers to be higher!
Next week I hope to carry out an FTP test, it will be interesting to see which unit gives me the higher FTP, I think on the basis of my investigations so far it will be the PowerTap.
PowerTap vs CompuTrainer Comparison.
|TSS||139.1 (IF 0.797)||138.7 (IF 0.796)|
|Peak 5s Power||530W||456W|
|Peak 10s Power||395W||386W|
|Peak 20s Power||318W||315W|
|Peak 30s Power||314W||310W|
|Peak 1m Power||287W||290W|
|Peak 2m Power||271W||272W|
|Peak 5m Power||248W||250W|
|Peak 10m Power||242W||244W|
|Peak 20m Power||231W||232W|
|Peak 30m Power||226W||229W|
|Peak 60m Power||224W||225W|