Monday, April 23, 2007

DIY aero testing

DIY aero testing.

The goal.
To see if there is a measurable difference in "aero-ness" between using my new aero lid, and using my old standard helmet.

An increase in "aero-ness" is crudely defined as the ability to do the same speed for less watts.

The location.
Outdoor velodrome at Haitaitai, Wellington NZ.
333 metre concrete track. (Bumpy).
Wind . Nil.
Temperature. 9-11 degrees.
From around 8am onwards.
Barometric pressure 1026 hpa.
Humidity 80%

The format.
8 runs. Completed in 1 hour and 15 mins with very little resting or downtime, apart from swapping helmets and noting temperature. Aero means Aero helmet, non-aero means non-aero helmet.
4 x 5 mins at 34 kmh. Aero, non-aero, aero, non-aero
2 x 5 mins at 40 kmh Non-aero, aero,
2 x 10 mins at 35 kmh. Aero, non-aero(35kmh seemed easier to do than 34 kmh)

The difficulities.
1. Getting the track to myself. (No problems)
2. Getting consistant wind . (No problems)
3. Getting consistant temperature. Pretty good.
4. Riding at a consistant speed. Way better than a previous attempt. The trick was to ride by feel (cadence?), rather than obsess on watching the computer.
5. Getting a smooth line. I rode on the sprinters line because it was way smoother than the bumpier pursuiting line. I guess this means I am less vertical than I could have been.

The equipment:

1. Bianchi d2 chrono TT bike and Power tap. Deep front rim. Weight around 9kgs
2. Carrera Dragon Fly helmet (Non-aero)
3. Louis Garneu Rocket helmet. (Aero)
4. Rider about 71 kgs. Add another 3 kgs for kit at least.

The "raw results"" are as follows, and have had no factors applied to them. They are listed in the order that they were undertaken.

Run number:
1. Aero. 5mins 34.6kmh 191 watts temp 9.3
2. Non-aero 5mins 34.5kmh 194 watts temp 9.9
3. Aero 5mins 34.7kmh 196 watts temp 9.4
4. Non-aero 5mins 34.5kmh 197 watts temp 9.8
5. Non-aero 5mins 40.2kmh 280 watts temp 9.9
6. Aero 5mins 40.5kmh 270 watts temp 10.9
7. Aero 10mins 35.1kmh 195 watts temp 11.4
8. Non-aero 10mins 35.3kmh 197 watts temp 11.4

To try to get an smooth transitition from start to finish, I would set my timer off for 5 mins, take two laps to settle in, then go another 2 laps after my time had elapsed, and stop pedaling on the line.

At the end of the day, after downloading this data, I would then "select" 5 mins worth of data, back from that coasting point, so all tests at least stopped in the same place.

The differences I recorded in the 40kmh test were pretty major, compared to the lower speeds, but I guess I would have to do it a couple of times to see if they were consistant and not some kind of an aberration. I think the last two runs are the least impressive as far as being decisive in any way, as the last run was actually faster than the one before it. If I am doing it right, I get a CdA of .233 using Alex Simmon's spread sheet. I am not sure if that is good or not.