Results / Riders
Time-trial position.
The question
Hannah rides a 40 km time trial at about 255 W. Her fitter had made her comfortable. She wanted to know how much speed the comfort cost, and which changes she could hold for an hour.
CdA before
0.262m²
CdA after
0.228m²
Power saved at 42 km/h
33W
Over 40 km at the same power
≈2½min faster
The runs
| Run | Change | CdA m² | W at 42 km/h |
|---|---|---|---|
| 01–02 | As she arrived (average of two) | 0.262 | 255 |
| 03 | Pads 4 cm lower | 0.249 | 242 |
| 04 | Pads 3 cm narrower | 0.241 | 234 |
| 05 | Extensions tilted up 10°, hands together | 0.236 | 230 |
| 06 | Head down, helmet tail on the back | 0.226 | 220 |
| 07 | Same, repeated | 0.229 | 223 |
| 08 | Pads a further 2 cm lower | 0.231 | 225 |
| 09 | Back to run 06, confirmed | 0.228 | 222 |
Watts are the power to push the air only: ½ × 1.225 kg/m³ × CdA × (11.67 m/s)³. Rolling resistance and drivetrain losses come on top and didn't change.
What she kept
Run 08 went lower again and measured worse: her shoulders rose and opened a gap in front of the chest. We went back to run 06's position and confirmed it.
The biggest single gain wasn't the bars. It was the head: tucked down so the helmet's tail sat on her back, which closed the gap the smoke kept rolling into. It is also the change that is hardest to hold, so we filmed her from the side at minute one and minute twenty of a hold test, and marked the head height on the video for her training.
“I'd been told to get lower for two years. The smoke showed me it was my head, not my back.”Hannah Pryce