Cycling Aerodynamics Explained: What Is CdA and How Many Watts Does Getting Low Save?
Two numbers to remember
- Above 30 km/h, 70–90% of total resistance is aerodynamic drag — and the share grows with speed.
- 70–80% of that drag comes from the rider's body, not the frame or wheels. That is why position always comes before purchases.
What is CdA?
CdA = drag coefficient (Cd) × frontal area (A), in m². Aero power ≈ ½ × air density × CdA × v³ — note the cube of speed: going from 30 to 40 km/h takes roughly 2.4× the aero power.
Typical CdA ranges for road cyclists (public research and field testing):
- Hoods: ~0.32–0.36 m²
- Drops: ~0.28–0.32 m²
- Aggressive road crouch: ~0.25–0.28 m²
- TT / triathlon aero: ~0.20–0.24 m² (elite down to ~0.18)
How many watts does getting low save?
At 40 km/h, every 0.02 m² of CdA is worth roughly 15W. Moving from hoods (~0.34) to drops (~0.30) commonly saves 20–30W; a disciplined aggressive crouch saves 20W more. At constant power that converts to 1–2 km/h of cruising speed.
See it with your own eyes in a wind tunnel
We built a free 2D fluid-simulation wind tunnel that runs in your browser: switch hoods/drops/aero and watch the flow field and relative drag change in real time — you can even upload a riding photo and put your own position into the wind.
Open the VeloTunnel ›The cost-effective order for cutting drag
- Position (free–cheap): lower the front end, narrow the elbows, keep the head stable — provided your flexibility and hip angle allow it. See torso angle vs power trade-offs.
- Tight-fitting clothing: a flapping jersey can cost you 10–20W.
- Aero helmet: ~5–10W at 40 km/h.
- Wheels/frame: ~4–8W — last not because it's useless, but because it's the most expensive per watt.
Bottom line: get your position both low and sustainable first — and whether you can hold it depends on saddle height, reach/stack and flexibility. That is exactly what bike fitting solves.
How much room does your position have?
Film a short side-view riding video with your phone for a free 4-angle quick check; the full AI analysis gives concrete saddle height / stack / reach numbers with step-by-step adjustments.
Free position quick check ›FAQ
What does CdA mean in cycling?
CdA is the drag coefficient (Cd) multiplied by frontal area (A), in square metres — a single number for how much air resistance rider plus bike create. Lower is faster: hoods ~0.32–0.36, TT positions ~0.20–0.24.
What share of cycling resistance is aerodynamic?
On flat roads above 30 km/h, aerodynamic drag is roughly 70–90% of total resistance, growing with speed. About 70–80% of that drag comes from the rider’s body rather than the bicycle.
How many watts does riding in the drops save?
At 40 km/h, moving from hoods to drops typically saves about 20–30W in field tests — worth roughly 1–2 km/h of cruising speed at the same power output.
Related: the single biggest free aero gain isn't equipment at all — it's riding behind someone. See how much energy drafting saves on a bicycle (27–50%).