Thus far, the Power Up series has focused on only one measurement device: the Quarq crankset. And while there are many other options on the market, they all share a fairly hefty price tag. Today we're going to look at one of the cheapest solutions there is, made by Kurt Kinetic. That's right, the company that primarily makes trainers has in its arsenal a bit of gear that calculates power based off of the trainer itself, or more specifically, how fast the flywheel is spinning.
So let me say that again. If you want to get into power on the cheap, all you need is a Kurt Kinetic trainer, and their $79 cyclometer. Of course, that means you have to be riding indoors to get power data, but there are pretty respectable riders who have no problem doing their training inside.
So how does it work? Kurt's fluid chamber is filled with a silicon solution that exhibits very predictable properties. It doesn't expand or change viscosity as it heats up, so its power curve can be very accurately calculated for a given range of loads. In fact, Kurt publishes the equation they derived for the trainers. The equation makes a couple of assumptions to narrow down the variables involved, such that all you have to plug into the equation is speed, and it will spit out power. How accurate is it? I found it to be very good, tracking my Quarq within a couple of percentage points. TrainerRoad did a more thorough analysis of its accuracy, and found basically the same thing that I did. One caveat is that changes in rolling resistance can have a measurable impact on accuracy, so make sure you crank the flywheel down to your tire with roughly the same amount of force. It's worth noting that Computrainer has a sensor to measure that force, so that you can get more repeatable results.
Now, if all that's required to derive power from these trainers is speed, then why do you need the computer? Well, because it has the equation built in - it will show you your power as you're riding. But the downside is that it will only show it to you live. There's no way to record and download the data for later analysis. Fortunately, there are other solutions available. As mentioned above, Kurt Kinetic very smartly published their power equation, and this opens the trainer up to more universal applications. TrainerRoad, mentioned above, is first and foremost a software package that lets you record your data straight to your computer via an ANT+ stick and a laptop. It's a pretty slick solution, and definitely worth a look. In fact, I'll be doing just that in Part 6 of this Power Up series.
Kurt Kinetic also has a couple more indoor-specific products that aren't directly-related to power, but are definitely germane to the topic of riding on a trainer, and worth a mention here. Hit the jump to read about Kurt's heavy-weight flywheel option, and their indoor-specific training tire.