How much does a headwind slow you down on a bike?
See what 10 to 40 km/h (6 to 25 mph) of headwind does to your speed and time, and how to pace it.
The short answer
A 20 km/h (12 mph) headwind slows a rider who does 25 km/h (15.5 mph) in still air to about 15 km/h (9.3 mph) at the same effort. That's why headwind cycling turns a four-hour 100 km (62-mile) ride into 6 hours 40 minutes, and a tailwind home never wins the time back.
Key takeaways
- A 20 km/h (12 mph) headwind cuts a 25 km/h rider to 15 km/h at the same effort.
- Air resistance rises with the square of the air speed hitting you, not your ground speed.
- An out-and-back in steady wind is always slower than the same ride in still air.
- Pace by power or heart rate, and plan time, food and light for the slower speed.
Definitions
- Headwind component
- The part of the wind blowing straight against your direction of travel.
- Air speed
- How fast the air moves past you, which is your ground speed plus the headwind component.
- Drag area (CdA)
- A single number for how much air resistance you and your bike create; lower means faster for the same effort.
What does a headwind actually do to you?
A headwind adds its speed to the air hitting you. That's the whole problem with headwind cycling: you push through far more air than your ground speed suggests. Ride at 25 km/h (15.5 mph) into a 20 km/h (12 mph) headwind and the air meets you at 45 km/h (28 mph).
Air resistance rises with the square of that air speed, so 45 km/h (28 mph) of air pushes back about 3.2 times as hard as 25 km/h (15.5 mph). On a flat road at 25 km/h (15.5 mph), air resistance is already about 70% of your effort. The bigger picture is in our complete guide to cycling in wind.
How much speed and time does a headwind cost?
At a steady effort, a 20 km/h (12 mph) headwind cuts a 25 km/h rider to 15 km/h and adds 2 hours 40 minutes to a 100 km (62-mile) ride. This table holds the effort that gives 25 km/h (15.5 mph) in still air, about 97 W.
| Wind, km/h (mph) | Your speed, km/h (mph) | Time for 100 km (62 miles) | Change, minutes |
|---|---|---|---|
| Still air | 25.0 (15.5) | 4h00 | 0 |
| Headwind 10 (6) | 19.6 (12.2) | 5h06 | +66 |
| Headwind 20 (12) | 15.0 (9.3) | 6h40 | +160 |
| Headwind 30 (19) | 11.4 (7.1) | 8h48 | +288 |
| Headwind 40 (25) | 8.6 (5.3) | 11h40 | +460 |
| Tailwind 10 (6) | 31.1 (19.4) | 3h13 | −47 |
| Tailwind 20 (12) | 37.8 (23.5) | 2h39 | −81 |
| Tailwind 30 (19) | 45.0 (27.9) | 2h13 | −107 |
A stronger rider, at the 152 W that gives 30 km/h (18.6 mph) in still air, loses less but still loses hours.
| Headwind, km/h (mph) | Your speed, km/h (mph) | Time for 100 km (62 miles) | Change, minutes |
|---|---|---|---|
| None | 30.0 (18.6) | 3h20 | 0 |
| 10 (6) | 24.3 (15.1) | 4h07 | +47 |
| 20 (12) | 19.4 (12.0) | 5h10 | +110 |
| 30 (19) | 15.2 (9.5) | 6h34 | +194 |
| 40 (25) | 11.9 (7.4) | 8h24 | +304 |
The assumptions behind these numbers
Every figure in these tables comes from the standard road-cycling power model, validated on the road by Martin and colleagues (1998). We assumed a flat road, a steady effort, no drafting and wind blowing straight along the road. Rider 75 kg, bike 9 kg and kit 2 kg: 86 kg (190 lb) in all. Drag area (CdA) 0.32 m² (3.4 sq ft), hands on the hoods. Rolling resistance coefficient 0.005. Sea-level air at 15°C (59°F), density 1.225 kg/m³. Drivetrain efficiency 97.5%. Your numbers will differ. The pattern won't.
Want this for your own route? Windline shows the wind for every stretch, timed to your pace. Free. Make a free ride page →
Why doesn't the tailwind pay back the headwind?
Because you spend far longer in the headwind. Ride 50 km (31 miles) out into a 20 km/h (12 mph) wind and 50 km back, and the same 97 W takes 4h39 instead of 4h00, an average of 21.5 km/h (13.4 mph).
The outward leg at 15.0 km/h (9.3 mph) takes 3h20; the return at 37.8 km/h (23.5 mph) takes 1h19. You fight the wind for nearly three-quarters of the ride. The stronger rider still loses 24 minutes (3h44 instead of 3h20). Which leg to ride first is covered in should you ride into the wind first.
How much harder do you have to push to hold your speed?
About two and a half times harder. Holding 25 km/h into a 20 km/h (12 mph) headwind takes about 248 W instead of 97 W. Holding 30 km/h (18.6 mph) takes about 359 W instead of 152 W.
Power is drag times speed, so in still air the power for the air rises with the cube of your speed: 10% faster needs about a third more (1.1³ = 1.33). In a headwind it's worse, because your legs pay for the air speed but only get credit for the ground speed.
What changes these numbers on a real road?
Mostly height and angle, and both usually shrink the real headwind below the forecast figure.
- Height. Forecast wind is for 10 m (33 ft) up, the World Meteorological Organization (WMO) standard. By the standard wind profile, wind at 1–1.5 m (3–5 ft) is about 60–70% of that over open grassland. A 30 km/h (19 mph) forecast on open ground is nearer 18–20 km/h (11–12 mph) where you sit. More in why the wind on your bike isn't the wind in the forecast.
- Shelter. Hedges, trees and buildings cut the wind; WMO notes their wakes can stretch 12–15 times their height downwind. Ridges, bridges and coasts expose you.
- Angle. Wind at 45° to the road gives about 71% of its speed as headwind.
- Gusts affect your handling more than your average speed: see how windy is too windy to cycle.
How much do tucking and drafting save?
Drafting saves far more than tucking. In a wind-tunnel study, moving from upright to the drops cut drag area by about 10% (Blocken et al., 2013). In our model, that lifts the 97 W rider from 15.0 to 15.8 km/h (9.3 to 9.8 mph) into a 20 km/h headwind: 20 minutes saved per 100 km.
Sitting right behind another rider, wheels almost touching, cut drag by about 27% in the same study. Earlier pace-line studies put following riders at 50–70% of solo drag; mid-pack in a big peloton it's 5–10% (Blocken et al., 2018). At 70% of solo drag, our rider does 17.7 km/h (11.0 mph) into that wind; at 50%, 20.5 km/h (12.8 mph).
How should you pace a ride into a headwind?
Pace by power or heart rate, not speed. Choose the effort you could hold in still air for the length of the ride, and accept the speed it gives.
- Don't chase your usual average. Holding 25 km/h (15.5 mph) into 20 km/h (12 mph) of wind takes 2.5 times the power.
- Plan time, not distance. 100 km (62 miles) takes 6h40 into a 20 km/h (12 mph) headwind. Carry food, water and lights for that.
Frequently asked questions
Is a headwind worse than a hill?
At the same effort, a 20 km/h (12 mph) headwind slows our model rider as much as a steady 1.8% climb in still air: both give about 15 km/h (9.3 mph) at 97 W. But a climb ends at a summit, while a headwind can last all day.
Does the rule of thumb "you lose half the wind speed" work?
Roughly, in moderate winds. A rider doing 25 km/h (15.5 mph) in still air loses 5.4 km/h into a 10 km/h (6 mph) headwind and 10 km/h into a 20 km/h (12 mph) one. Beyond that the loss falls below half, but your time still climbs steeply because every kilometre takes longer.
Does riding into a headwind burn more energy?
Per hour, no: at the same power you do the same work every hour. Per ride, yes, because you're out for longer. Our 97 W rider does about 1,400 kJ of work over 100 km (62 miles) in still air and 2,330 kJ into a 20 km/h (12 mph) headwind. Plan food for time on the bike, not distance.
How do I work out the headwind on my own route?
Take the forecast wind speed and direction for the hour you'll ride each stretch, then compare the direction with the way the road runs. Wind straight on the nose counts in full; wind at 60° to the road gives half its speed as headwind. Our guide to [reading wind direction](/blog/wind-direction-explained/) shows the method step by step.
What headwind is too strong to ride in?
There's no single safe number, and speed loss isn't the main risk. Gusts and crosswinds are, because they can push you sideways into traffic or off the road. Official weather warnings always come first. Our [decision table for windy rides](/blog/how-windy-is-too-windy-to-cycle/) maps wind and gust speeds to the Beaufort scale.
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Make a free ride page →Sources and method
- Journal of Applied Biomechanics (1998). Validation of a mathematical model for road cycling power (Martin, Milliken, Cobb, McFadden and Coggan)
- Computers & Fluids (2013). CFD simulations of the aerodynamic drag of two drafting cyclists (Blocken, Defraeye, Koninckx, Carmeliet and Hespel)
- Journal of Wind Engineering and Industrial Aerodynamics (2018). Aerodynamic drag in cycling pelotons: new insights by CFD simulation and wind tunnel testing (Blocken et al.)
- World Meteorological Organization (2018). Guide to Instruments and Methods of Observation (WMO-No. 8), Volume I, Chapter 5: Measurement of surface wind
Speeds, times and power were calculated with the standard road-cycling power model (Martin et al., 1998, "Validation of a mathematical model for road cycling power", Journal of Applied Biomechanics 14(3)), solving for the steady speed at which the rider's power, after drivetrain losses, equals air resistance plus rolling resistance. Flat road, steady effort, no drafting, wind blowing straight along the road. Assumptions: rider 75 kg + bike 9 kg + kit 2 kg = 86 kg (190 lb); rolling resistance coefficient 0.005; drag area CdA 0.32 m² (hands on the hoods); air density 1.225 kg/m³ (sea level, 15°C); drivetrain efficiency 97.5%. The first rider holds the effort that gives 25 km/h (15.5 mph) in still air (about 97 W); the second holds the effort for 30 km/h (18.6 mph) (about 152 W). Out-and-back times are 50 km (31 miles) into the wind plus 50 km (31 miles) with it. Air resistance at 25 km/h in still air is about 67 W of the 97 W (69%). The drops figure applies the 10% drag-area reduction measured by Blocken et al. (2013), upright to dropped position (0.270 to 0.243 m²), to the same model; the drafting figures apply 70% and 50% of solo drag, the small-group range reported by Blocken et al. (2018). The equivalent climb is the steady gradient that gives the same 15.0 km/h at 97 W in still air (1.8%). Work in kJ is power multiplied by time. Wind at rider height uses the neutral logarithmic wind profile, U(z) proportional to ln(z/z0), between 10 m and 1–1.5 m, with roughness lengths of 0.03 m (open flat grassland) and 0.10 m (low crops) from the WMO terrain table in WMO-No. 8. Imperial conversions use 1 mile = 1.609 km and 1 kg = 2.205 lb.
About the author
Wes Thomson, Founder, Windline. Wes Thomson builds Windline, live wind and weather forecasts timed to when riders reach each stretch of road. He built it for his own 2,093 km tour from Pont Drift to Cape Town, and writes these guides with the same focus: what the wind will do to your ride, and how to plan around it.