Cycling power calculator
Cycling power splits into three terms: air, rolling and climbing. Air wins above about 25 km/h and gravity wins on any real hill.
m2
%
kg/m3
%
Power required
5583.1W
- Power lost to air
- 5292.0 W
- Power lost to rolling
- 123.6 W
- Power against gravity
- 0.0 W
- Air as a share of the total
- 97.7 %
- Watts per kilogram
- 74.441
- Calories per hour At about 24% gross metabolic efficiency.
- 83 746 kcal/h
Show the working
- Speed = 30
- Rider mass = 75
- Bike mass = 9
- Drag area CdA = 0.32
- Rolling resistance = 0.005
- Gradient = 0
- Air density = 1.225
- Drivetrain efficiency = 97
- v = 30 = 30
- total_mass = 75 + 9 = 84
- Power lost to air = 0.5 * 1.225 * 0.32 * 30^3 = 5292
- Power lost to rolling = 0.005 * 84 * g0 * 30 = 123.564
- Power against gravity = 84 * g0 * 30 * 0/100 = 0
- p_wheel = 5292 + 123.564 + 0 = 5415.56
- Power required = 5415.56 / (97/100) = 5583.06
- Air as a share of the total = 5415.56 > 0 ? 5292/5415.56*100 : 0 = 97.7184
- Watts per kilogram = 75 > 0 ? 5583.06 / 75 : 0 = 74.4407
- Calories per hour = 5583.06 * 3.6 / 0.24 = 83 745.8
Values are shown to six significant figures here; the arithmetic itself runs on exact fractions and is only rounded where a number is printed.
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The formula
- P = 0.5 rho CdA v^3 + Crr m g v + m g v sin(theta), all divided by drivetrain efficiency
Air resistance grows with the cube of speed. Going from 30 to 35 km/h costs roughly 60% more power on the flat.
A CdA of 0.32 m2 is a rider on the hoods; 0.25 on the drops and 0.21 in a good time-trial position.