Over the weekend I went for a ride on my time trial (TT) bike for the first time since racing in Dallas last October. The black Beyond Fabrications frame is the same bike I rode in 2007 when I won Amateur Worlds in Germany, but I’ve made a few key upgrades to it. Most recently, I added an SRM Dura-Ace powermeter, which uses ANT+ wireless technology to pair seamlessly with my Garmin Edge 705. On my road bike I’d been using a Quarq CinQo powermeter for about a year and a half, and I was excited to see how the SRM’s performance would compare.

My Edge 705 display is set to show seven data fields (out of a possible on the main page: Lap Split, Heart Rate, Power (3s running average), Cadence, Speed, Distance, and Energy (Kilojoules). I use the 3s average because typically power data sampled at higher rates is not steady enough to follow. The Edge 705 also has an option for 10 second averaging, which gives an even better idea of the steady state wattage you’re pushing.  The Energy setting is really nice to look at instead of distance as a measure of how hard I have worked. A Kilojoule (KJ) is power multiplied by time. So if you push one thousand watts (kilowatt) for one second, you’ll produce 1KJ of energy. Or – if you’re human – you may produce a KJ by pedaling 125 watts for 8 seconds, or 200 watts for 5 seconds… you get the idea. To help you conceptualize, a kilowatt hour – like the ones you pay for every month on your electricity bill – is equal to 3,600 Kilojoules. In my three-hour, 55 mile ride on Saturday I produced just under 2,000 KJ (connecting your trainer to a power generator will not save you much money). A few weeks ago, however, I rode three hours and covered only 50 miles of pavement, but produced 2500 KJ of energy because the terrain was significantly more difficult, the weather was worse, and somehow the downhill sections still required pedaling.

Back to my first impressions of the SRM powermeter.  Without a calibrated ergometer to test both powermeters side-by-side, I can’t make a claim for which is more accurate, but judging by how they perform during rides on a computrainer, both seem to provide data precise enough for me to rely on it during my training and racing. The big difference between my two units is the quality of the crank that the powermeter is mounted to. The Shimano Dura-Ace cranks and chain-rings of my SRM are much higher quality than the FSA Team cranks on my early-issue Quarq CinQo. Quarq now sells their product on more reliable crank systems (from SRAM, Specialized, even Rotor). Otherwise, I can’t tell a performance difference – they both work very well.

To learn more about viewing Power data on your Edge 705, check out this video from Garmin’s online learning center.