I have been using the new PowerCal chest strap from Cycleops for the last few months. If you are like me and you have several bikes, and you also like to train with power, it is difficult to afford to outfit all your bikes with the latest greatest power meters. So, when a riding buddy of mine told me about the Cycleops PowerCal, and it only costs around a hundred bucks. I was instantly interested. The PowerCal is a device that you wear just like a heart rate strap, in fact it replaces your current heart rate strap and it communicates to your computer, Garmin or other device, and fakes your device into thinking you have a power meter connected. You then just setup your device to show whatever power related data fields that you want to monitor and the rest is as easy as just going for a ride. The device turns your heart rate data into a power reading that you can then upload to Training Peaks or Strava for analysis. I won’t go into all the details on how the thing works. DC Rainmaker has a great review with lots of detail that you can read about here.
But suffice it to say that the device uses your heart rate to predict power wattage. I was skeptical, as I am most of you are too. I have computrainer at the shop so I figured i would use it to compare my watts. I ran an ftp test on the computrainer and came up with a reasonable number that I believe is accurate. Then, for the last few months I have been wearing the PowerCal strap during rides and races. I have compared my peak 30 minute watts during race conditions to my computrainer ftp test and the numbers are within 2 watts. Pretty impressive. So with information I was very curious just how this thing works. After reading DC rainmakers detailed review, and the tech data that is posted on the Cycleops website, they way i understand it is; the device has an algorithm that doesn’t just read heart rate. It also reads the the rate of ascent and the rate of descent of your heart rate in order to determine a power wattage number. And here is where I am calling bullshit, I think there is more going on in there than what Cycleops is willing to tell us. I understand they may not want to reveal everything as it may be easy for manufacturers to duplicate if revealed. Here is why I think there is more. When i am pedaling and working hard I look down at the power meter and it shows an appropriate looking heart rate and an appropriate looking power output, but then i will stop pedaling and coast and the power output drops, even though my heart rate has remained the same. So if it is solely based on heart rate how can this be? Now I know this is really not a super scientific test, but it seems like a reasonable situation and one that is not answered by Cycleops description. In any event, this little bicycle accessory device is amazing and for everyday use it accurate enough for me. Now i can have pseudo power readings on any bike I happen to be riding which is pretty cool.