The hour record: how much power it takes and why CdA and air decide as much as legs

To ride 56.8 km/h for an hour, the model asks for about 400 W with a CdA of 0.16 m² and thin air, and more than 530 W with a CdA of 0.21 m² and dense air. The gap between those extremes is larger than the one separating many professional riders: in the hour record, CdA and the air decide as much as power.

How much power does each average speed take?

On the track, with no wind or gradient, almost all the power goes into beating the air, and rolling resistance is small because tubulars on wood roll very well^2,3. Because drag grows with the cube of speed, each extra kilometre per hour costs more than the last.

Every hundredth of CdA (0.01 m²) is about 22 W at that speed. Going from 0.19 to 0.17 m² is equivalent to gaining 45 W of sustained power for an hour, something training only achieves over years.

Why do the velodrome and the day matter so much?

Air density changes the outcome as much as CdA. An indoor velodrome lets the temperature be raised, which lowers density. Altitude lowers it further: at 450 m and 25 °C, as in Grenchen, air is around 1.12 kg/m³; at about 1880 m, as in Aguascalientes (Mexico), it drops to about 0.94 kg/m³.

But altitude also reduces aerobic power, by around 6 % per 1000 m in endurance athletes⁴. Models comparing hour records at different altitudes show that balance between lighter air and lost power¹. Up to what altitude it pays depends on how much each rider loses, which varies widely between people. We explain it in more detail in air density, altitude and speed.

How is an attempt planned?

• Measure CdA on the track itself, with the day’s equipment and position, because on bends and banking it is not the same as on the road (see how to measure CdA).
• Calculate the target power using the forecast density in the velodrome at the time of the attempt.
• Choose the gear: at 56.8 km/h and 105 rpm you need about 9 metres per pedal revolution. You can work it out with the track gear calculator.
• Pace by lap times: over an hour, an almost constant pace is the most efficient, because any acceleration costs far more than it returns.

Rule of thumb: at that speed, 0.01 m² of CdA is worth about 22 W, and 1 % of air density about 4 W. Before chasing watts, chase CdA and a good day.

What is known and what is not

The power model is validated on the road and explains most of the variation in measured power². On the track there are effects this simplified version leaves out, such as rider lean in the bends and the extra distance ridden outside the measurement line, which raise the required power somewhat. Reviews of cycling performance agree that aerodynamics is the dominant factor at these speeds⁵.

Frequently asked questions

How many watts does the hour record take?

For 56.8 km/h, between about 400 and 540 W depending on CdA and air density, with this article’s model.

Why is the hour record attempted at altitude?

Because the air is less dense and drags less. In exchange, the body produces less power, so altitude only pays up to a point.