Recently, I purchased an iBike Sport from Competitive Cyclist. Frankly, I was in need of a new cyclocomputer, and I have been wanting to try one of these to see how well it works as a power meter so I gave it a shot. I should clarify something; the iBike is not really a power meter but more of a power estimator because it doesn't use strain gages for measurements like other popular power meters do (Powertap, SRM, Quarq). Instead, it measures wind speed and the road gradient, and then calculates how much power is theoretically required for a certain rider to be traveling at the given speed. These calculations are based on several assumptions taken as constants, such as aerodynamic and rolling resistances, so there are some inherent deficiencies in the calculations (such as not being able to account for changes in positions, like going from the tops to the drops). But overall, this test done by VeloNews suggests that the calculated real-time power readings from the iBike correspond pretty well to those from a PowerTap.
More after the break...
Anyways, things didn't get off to a good start for me with the iBike. This is because the wind sensor of the first unit that I received from Competitive Cyclist was defective. I promptly sent the unit back to Velocomp (iBike's makers), and in my opinion it took them much longer than it should have to send me a new one. I finally got the replacement unit after about two weeks, and thankfully this one worked well right out of the box. After installing the mount and the sensors on my bike, I went through the quick setup procedures, did the 2-mile calibration ride, and I was ready to go.
Built into the iBike is a fitness test that measures your average power output over a 20-minute period (expressed in terms of watts per kilogram, or W/kg). Basically, you go all out for 20 minutes and see what you can do. I figured this would be a good way to test this thing and myself out, so I went to a local multi-use path that is a 7-mile asphalt paved loop with fairly light traffic to minimize interruptions. See, I would like to think I have a pretty good idea where I stand as a cyclist, and the W/kg reading resulting from the 20-minute test allows me to assess my fitness level using published charts/tables, such as the Allen & Coggan race category table shown towards the bottom of this page.
As far as my riding abilities go, I consider myself a slightly above average cyclist. I used to race a little when I was in graduate school about 5 years ago, but I haven't done any racing since then. I am a lot heavier than what my race weight was (225 lbs today vs. 175 lbs back then, at 6'0" tall), but I can still pedal along at a decent pace as long as the roads stay relatively flat. Gravity pretty much always wins when it comes to hills...
So, I went all out for 20 minutes and the iBike showed an average power output of 245 watts, giving me a W/kg value of approximately 2.4. Looking at the Allen & Coggan table, this puts me just above the "untrained" category and at the bottom of "Fair - Cat 5" category. I think this is probably not too far from the truth, given that I ride with some Cat 4/5 riders from time to time, and the good ones always drop me towards the end. For reference, I covered a total distance of 7.6 miles in these 20 minutes for an average speed of 22.8 miles per hour. Also for what it is worth, the analyticcycling.com website estimates about 240 watts would be required for someone my size (assuming a frontal area of 0.6 m^2) to achieve 22.8 miles per hour (10.2 meters per second) on a flat, asphalt road.
I also figured I would try and see what the maximum power I can generate in a sprint is, and pegged the iBike at 1,484 watts. This puts me at approximately 14.5 W/kg. Referring to the Allen & Coggan table again, this puts me near the top of the "Moderate - Cat 4" category. I have always thought I have a pretty decent sprint, as I usually contest for the win in our Saturday morning fast group ride, so again this is probably not too far off either.
So in short, I think this is a useful device that appears to do a decent job of estimating power based on my experience as well as other parties such as VeloNews. To be quite honest, I was not too worried about absolute accuracy when I purchased this unit as long as it was consistent, and so far it seems to be pretty good at that based on my initial experiences. I still haven't had a chance to evaluate some of its potential quirks (like the effects if riding in a group) because I took apart the bike that the iBike is mounted on shortly after this initial test, and I have been too busy/lazy to put it on my other bike. But based on what I have seen so far, I think it will make a good training companion (it has suggested training programs based on the results of your fitness test). I also think I might upgrade to the Pro version so that I have the ability to download and better analyze the data. Either way, I will report on my future experiences when I have had some more time with the unit.