14
Jun
10

2%.

A poor head-on shot of my TT position.

The world of Time Trials is really, really complex. In many ways, it’s “The Race of Truth”, but in many ways, it’s also a race of technology. The pursuit of an aerodynamic edge, be it wheels, frames, helmets, or skinsuits, really can mean the difference between hitting the podium, and missing it.

This weekend, I raced an awesome looped course, complete with rolling terrain, different types of pavement, and an increasing wind. It was incredibly fun and challenging, but when the results were posted, I had missed the money by ONE second, and I had missed the win in my category by just about a minute. Let’s play around with some numbers here and there, look at wattage values, and see if we can figure out a way for me to increase my speed and reduce my time, just by using technology.

Over the years, I’ve tried to use technology to influence my positioning on the Time Trial bike, and also to influence my purchasing decisions, so everything tends to be tilted towards that which will produce the lowest amount of drag, while still allowing me to generate adequate power to the pedals. For this event: here’s my equipment list:

  • Aluminum Cervelo P3.
  • Aerobars
  • Oval TT fork
  • Nimble Trispoke up front.
  • Bontrager Aeolus Disc Wheel in rear (2007 model?)
  • TIGHT skinsuit
  • Louis Garneau aero helmet.
  • Pearl Izumi Booties

I opted to not bring a water bottle, though honestly, I should have considered wearing my camelback with a couple of ice cubes inside, but I don’t think my performance suffered from dehydration. I drank adequately prior to the effort, knowing I would lose fluids through perspiration and respiration from the stress and the environmental conditions.

Using Golden Cheetah’s experimental “AeroLab” and also a tried-and-true program from “Analyticcycling.com”, I took a section of road that was smooth and steady in its’ slope, where I knew I was in my aero position as consistently as I could remember, and I tried to determine my Coefficient of Aerodynamics, or CdA.

You try to get the lines to mesh as much as possible.

For the second image, take Frontal Area and multiply it by the Coefficient of Wind Drag. Both numbers come up close to a .265m^2, which is better known as the “HOLE” you cut through the air when you’re in a certain position. Remember, I lost 3rd place by 1 second, and I lost the victory by one minute exactly. The difference then, between 4th, which I got, and first, which we want, is about 1.8%. Thus the title of this post – a 2% improvement in my time would have earned me the win. I may have been able to pedal faster, but honestly, from what I know about aerodynamics, my .265m^2 is probably a little high. I’d like to see if I can lower that CdA down to a .25 or a .24 without losing power, and see what that would achieve.

Here are the results of some Analytic Cycling calculations. Notice the DROP in watts required to travel at the same speed. We’ll go back to my original power average on the last image….

Wattage required at .25m^2

Wattage Required at .24m^2

The savings on watts at the same speed, 10.2 meters per second, goes from 252w to 243w to 237w, or a savings of 3.5% and then 2.4%, or a total of 6% decrease in the amount of power required to hold that speed. So, you’re doing less work, using less energy, to get down the road at the same speed. Now, let’s show the final chart, and reveal just what speed I would have held on that section, had I been able to hold a .24m^2 aero position, and still generate 250w…

250w at a CdA of .24m^2

My speed goes up from 10.2m/sec to 10.44 m/s, or….

2.2%.

Now, this is never a perfect science, but let’s just say that I was able to mostly hold that position, stay at a perfect .24m^2 CdA, and generate 250w, which is about what I pushed on Sunday.

I averaged 25.3 miles per hour, or 11.3 m/s.

a 2% improvement would have yielded an average speed of 25.8mph, or 11.53m/s.

Covering the distance of the TT route, a 2% improvement would have yielded a 55:07, which would have put me 2 seconds out of 2nd place. Raising my power to 252w would have put me down in the 54 minute range, which would have led to a a win in my category.

So what’s the moral of the story? Well, as much as I love power, let’s face it – time trials are almost always won by mere seconds. Never let up, push as hard as you can as long as you can, but remember the little stuff that can, and does, make a difference.

Now – if I can just find a way to shed that drag, ever so slightly! Stay tuned!!!

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