Thursday, April 12, 2007

Power to the people - power meters for serious cycling

When I started this riding gig I was 16 and it was 1973. The bike was an Aussie-made Alcon, circa late 1930s and well looked after, if hand-painted. 28inch tyres, 40spoke wheels, diamond outrigger with sliding adjustment for handlebar reach and just 2 cogs on the back. On one side of the wheel was a freewheel and the other a fixie. Cool way to get started, eh? Even cooler was the mechanical odometer that clicked over incrementally with every turn of the front wheel. Ahhh, data! I started writing it down. Curiously it made me ride a bit more, just to get a scrap more data.

In the 1980s I found myself with electronic assistance in my data habit: a cycle 'computer', although all it really did was count wheel revs using a magnet and show elapsed time. It did allow me to see my current and average velocity, rather than doing the usual sums at home after the ride. And it was more accurate than some of the guesstimates I had to make. Now that sort of technology got a bit better over the last 25 years or so, but essentially remains as it was: a bunch of data based on wheel rotation over time, displayed on an LCD. (Although some of these new options are very sophisticated: check out BikeBrain for example)

Now this did make me ride for longer distances, and do more miles each week, as I could actually and accurately see when I had slacked off. And being data-obsessed I just wanted to push teh totals ever higher. Funnily enough I still had to chase down attacks, stick with the peleton over varying terrain and avoid being dropped, irrespective of what the displayed velocity was. But now I could also go 'ah, look at that average' after a hard crit.

The next leap forward in this history lesson was to the heart rate monitor. In my case it was the mid 90s and a Polar HRM. So now I could match perceived exertion against both time and distance, as well as estimate my caloric budget. It again made me ride, just to get data. Bizarre, I know. I wanted to exceed 200bpm on my local tough climb and set ever higher averages, so again I could go 'wow, that was a tough ride'.

Which brings me to my newest desire: power measurement. Up to now I've calculated it after the ride, inexactly, and longed to know how many Watts it really took to ride that hard crit. SRMs, offering measurement at the crank seemed a great option. But SRMs were (and remain) waaay too expensive, especially now I had kids to feed. The hub-based CycleOps option was still a bit rich (and what if I swapped wheels?) and Ergomo Pro was again a tad exxy and suffered (like the SRM) from being integrated into the bike. The Polar option was both expensive and tricky to set up. So I looked at the next-best options - the German HAC4 and other options from Germany and Italy, which calculated power from time, speed and altitude gain using accelerometers or barometric changes. Of course this only works on hills, but it was an option. Some of these options don't offer download, so it would be a 'write down later' sort of thing - like back to the 80s.

The HAC4 looks great options-wise but is a bit expensive compared with low-end 'real' power meters. I also looked at GPS units like Garmin's and wondered why no-one had integrated the coolest features into one unit. Maybe one day, I guess.

Anyway, I flipped a coin and went with the simplest, cheapest real-time data logging power meter I could find. The ibike. It back-calculates power by measuring the opposing forces - wind, friction and inclination - and comparing it to real speed (using a magnetic pickup). Easy to fit, easy to use. It looks the goods but does rely upon (a) your calibration accuracy and (b) unimpeded airflow. Which is to say that it misreads power if you aren't good at entering data (weight, aerodynamic and friction data, basically, although the latter is derived by the "coasting" test) or have impeded airflow (in a bunch, maybe, and certainly in a sharp corner).

I ummed and ahhed about this for weeks (whilst watching the Aussie to $US exchange rate fluctuate, too) and wondered if I really needed to spend $A580 on a gadget. I decided it was now or never and pressed the "buy" button in the ibike website. I'll tell you more later...

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