Thoughts on Indoor Time Trials, Power, and Aerodynamics


2011/02/19

The last indoor 10k time trial was last Sunday, February 13th. I rode all four of the monthly events starting last November. Starting with November, my results were 356 avg wts/4.5 wts per kg/time of 15:02, 364 avg wts/4.68 wts per kg/ time of 14:57, 382 avg wts/ 4.91 wts per kg/ time of 14:46, and finally 379 avg wts/ 4.87 wts per kg/ time of 14:39. Obviously with an indoor time trial there is no aerodynamic advantage for any rider. This simply a matter of watts per kilogram. If you go to the results at www.w8ds.com, you'll see that for the most part the highest wts/kg in each category was the winning time for that category.

From the first tt to the last I improved my time 23 seconds but this also required 23 extra watts on my average. If we look at the relative numbers I added 6.7% to wattage average but only improved my time by about 2.5%. This doesn't seem like the best return on your investment in power, especially when you consider that riding outside that the increase in wattage isn't a straight percentage but an exponential increase due to aerodynamic drag. My time would likely have improved even less outside if we assume no head or tail winds.

I also did four indoor 20k tt's at NKU with similar results although it was a perfectly flat course. I think the course in Dayton, with its hills, allowed for improvement in riding efficiency. This would account for my last ride showing a lower wattage avg and per kg while I went faster. Looks like I improved my downhill efforts to pick up speed while not going higher on the power in between.

I guess what these indoor tt's show is that improvement in aerodynamics could be the better pay off when riding outside. The energy it takes to add more power to overcome the resistance of the air has a minimal return compared to gaining more speed by being as aero on the bike as possible. And remember that your position accounts for 80% of the aero equation. Its not always about the most aero frame. In fact we know that the skinsuit and helmet mean more than the frame as do the wheels. I'm not at all saying power isn't relevant! you still need to take power as high as possible but at some point you have to take into account other ways to improve your avg speed and finishing times.

For road racers, there is a lesson here in that you want to conserve power until absolutely needed, be aero on road bike, use downhills to your advantage, and in general ride as efficiently as possible. We all know that being the strongest rider in the pack isn't a guarantee of winning. You have to ride smart and play to your strengths.







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