Table of Contents
Understanding Cycling Power
Power in cycling is measured in watts and represents the rate at which a cyclist does work. Total power required to maintain a given speed is the sum of three main resistive forces: aerodynamic drag, rolling resistance, and gravitational force (on gradients). On flat terrain at moderate speeds, aerodynamic drag accounts for 80-90% of total resistance.
Watts per kilogram (W/kg) is the most important metric for comparing cyclists, especially on climbs where gravity is the dominant force. Professional Tour de France climbers sustain around 6-6.5 W/kg for 30-40 minutes on major climbs.
Power Calculation Formula
Where ρ is air density (1.225 kg/m³), CdA is the drag area, Crr is rolling resistance coefficient, m is mass, g is gravity (9.81 m/s²), and v is velocity in m/s.
Power Benchmarks
| Rider Level | FTP (W/kg) | FTP (watts, 75kg) |
|---|---|---|
| Beginner | 1.5-2.5 | 112-188 |
| Recreational | 2.5-3.2 | 188-240 |
| Competitive amateur | 3.2-4.0 | 240-300 |
| Cat 1-2 racer | 4.0-5.0 | 300-375 |
| Professional | 5.5-6.5 | 413-488 |
Aerodynamic Drag Explained
- CdA of 0.32: Typical hoods position on a road bike.
- CdA of 0.27: Aggressive drops position.
- CdA of 0.22: Time trial position with aero bars.
- Reducing CdA by 10% saves more watts than reducing weight by 10% on flat terrain.
Frequently Asked Questions
How many watts does it take to ride at 30 km/h?
An 80 kg rider on flat terrain in a standard hoods position needs approximately 120-150 watts to maintain 30 km/h. Doubling to 60 km/h requires roughly 8 times the power (about 400-500 watts) due to the cubic relationship between speed and aerodynamic drag.
What is FTP?
Functional Threshold Power (FTP) is the maximum power you can sustain for approximately one hour. It represents your lactate threshold and is the most commonly used benchmark for cycling fitness. FTP is typically estimated from a 20-minute all-out test (multiply the average by 0.95).
Does wind affect power needed?
Yes, significantly. A 15 km/h headwind at 30 km/h riding speed is equivalent to riding at 45 km/h in still air aerodynamically. Conversely, a tailwind dramatically reduces power requirements. This calculator assumes still air conditions.