Thursday, February 12, 2009

Getting aero

Well, it's been over two months since I updated this thing. I guess all 3 people who read my blog (including myself) are begging for an update. So, since I am have a slight cold right now and am refusing to leave the couch I might as well update. Plus, there's only so many times you can check people's Facebook status.

Recently I went down to spend a week in Boca Raton doing some work and 09 planning for iBike. I took my time trial bike down there since the biggest hill was a bridge and I'd be riding a lot of flat roads. I always thought I had a pretty decent time trial position. I could have the handlebars pretty low and my back was definitely flat.

The only problem with this was that with my arms flat like that, and kind of far apart so I could breath, I had a huge pocket of air going right between my arms in into my chest area. I tried to position my arms upward a little bit to cut down on this gap. This made my back even lower, and it felt pretty fast. . .but I could barely push out 300 watts on the TT bike for 12 minutes. That's not going to win any time trials.

So I moved the bars back down, did some testing and found out that with training wheels, jersey, shorts, a regular helmet, a bottle, and a seatpack, my cda (drag coefficient) was .246. This is fairly decent and that number goes down (lower drag is better) when I have full race gear (like in the picture). I plugged the numbers into an online wattage calculator, and could see that for the Lowes Speedway Time Trials, the watts I usually sustain (340-345 for 20 minutes), and this cda gives me a time of just over 20 minutes. My normal time at Lowes is usually just over 20 minutes.

Then, the other day I got a crazy idea. . .what if instead of trying to go lower, I flipped my stem so it was higher? If I was higher, I could then angle my arms upward to cut down on the pocket of air entering my chest. I could also move the bars and pads even closer together to make myself more narrow. So I made the changes. The elbow pads are now in a position to that my forearms almost touch each other. The aero bars are about 3 inches apart, and angle upward. I decided to ride in this position before testing the cda numbers. I felt very comfortable, like I could produce the same power that I do on my road bike, and best of all. . .the bike felt faaaaast.

Once I got everything all set and rode around for a bit, I decided to test out the drag coefficient numbers. I was very pleasantly shocked to find that my cda had actually lowered by .02 despite raising my handlebars. Under the exact same clothing and equipment setup as before, my new cda was .223. I went back to the online wattage calculator and plugged in some more numbers.

If my wattage held the same as before, my time at Lowes would go from a 20:30 (no race gear setup) to a 19:50. Now, with race gear on I was usually getting around a 20:10 or so, so hopefully I will be able to put out a time closer to 19:30. Of course this depends a lot on weather conditions.

To get my cda numbers, I was using the combination of the Quarq crankset and the iAero head unit. This combination has the ability to display live cda as you are pedaling. If you stand up for a moment, you will see your cda go up. . .AND you will be able to see how much time it cost you as you are riding. And, given the accuracy of the time at Lowes Speedway given wattage and cda numbers, this combination can really be helpful for anybody wanting to go faster. I will try to get a couple of pictures up soon of my new time trial position and hopefully this will help me be a bit more competitive in my weakest event.

No comments: