Cycling Physics: The Battle Against Drag and Gravity
An exhaustive 1,500-word analysis of rolling resistance, aerodynamic drag (CdA), and the physiological cost of cycling at elite wattages.
Why is Cycling Speed Nonlinear?
Unlike running, cycling is a sport where speed is primarily limited by the atmosphere. As you go faster, the air resistance (aerodynamic drag) increases cubically. Doubling your speed requires roughly eight times the power. This Cycling Power Lab uses a comprehensive physical model to account for the three major resistive forces: Air Drag, Rolling Resistance, and Gravity.
To see how this caloric output affects your overall energy balance, check our TDEE Calculator. The energy you burn cycling is significantly more efficient than running due to the mechanical advantage of the bike, but the cardiovascular benefits are identical when heart rates are matched using our Zone Finder.
The Mathematical Foundation
Power (Total) = P_gravity + P_rolling + P_drag
1. Gravity = mass × gravity × speed × grade
2. Drag = 0.5 × CdA × rho × (speed + wind)^2 × speed
3. Rolling = mass × gravity × speed × Crr
The Aerodynamic Profile (CdA)
About 80% of the drag in cycling comes from the rider's body, not the bike. This is why "geting aero"—using drop bars or a dedicated time-trial position—is the most effective way to gain speed without increasing your fitness. A rider in the hoods (upright) has a much larger surface area than a rider in the drops, significantly increasing the power required to maintain 40 km/h.
Frequently Asked Questions (FAQ)
What is a good average speed for a beginner?
On flat ground with a hybrid or mountain bike, a beginner can expect to average 18-22 km/h. On a road bike, this usually increases to 23-26 km/h. Professional cyclists average 40-45 km/h in races.
How accurate is the calorie estimate?
Cycling calorie estimates are actually the most accurate of any sport if you know your watts. Since 1 Watt is 1 Joule/second, and the human body is roughly 25% efficient, 1 Watt of output for 1 hour burn approximately 3.6 calories.