Sunday, January 28, 2007

Slow January TTs

It's natural to want to compare recent time trial or wattage tests to results from older tests to track your progress. Some of my recent testing TT results didn't make sense to me when I compared them to numbers I got on the same course about 6 months ago. But after accounting for temperature effects, they look better.

I found that for my 10.66-mile time trial course, a decrease of 45 degrees Farenheit increases the air density enough to slow me down and increase my TT time by about 50 seconds. That's a very significant amount of time that has to be accounted for when comparing summer and winter outdoor timed tests.

The extra clothing worn at 45 degrees also would obviously increase my drag coefficient as well, and would result in a small increase in my weight (although not as much as January's proximity to Christmas). It wouldn't surprise me to find that the combined effects of January air teperature, drag coefficient, and weight combine to slow me down by 2 minutes or more for a half-hour TT when compared to the same course in July. That's something to think about when the numbers aren't so great for the winter tests.