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Cycling headwind calculator

See what a windy out-and-back costs at your planned power, how strong the forecast wind is likely to be at handlebar height, and how much riding harder into it wins back.

Your ride

Your target average for the bike leg, as your power meter reports it. Accepts 50 to 600 W, whole watts.

On a flat course only rolling resistance uses this, so a rough figure is fine. Accepts 30 to 200 kg.

Drag areas estimated from wind-tunnel measurements; see the notes below the calculator. A field-tested figure is better if you have one.

The whole course, out and back. Accepts 5 to 300 km.

Race distances

The wind

The mean wind, not the gusts, blowing along the course. Accepts 0 to 60 km/h.

Where the figure comes from
Ground the course crosses

Roads lined with trees, hedges or buildings are not offered: the wind there depends on the obstacles, and no height correction can predict it.

This wind costs about 13 min 10 s at a steady 180 watts.

At a steady 180 W

This wind costs about 13 min 10 s

On a calm day this ride takes about 2 h 41 min at 33.6 km/h.

A 30.0 km/h forecast is about 18.1 km/h at rider height over open flat ground (× 0.60).

Where the time goes

Distance

Riding time at a steady 180 W

Into the wind (striped)With the wind
Into the wind
23.5 km/h
34 min 20 s slower than a calm half
With the wind
45.5 km/h
21 min 10 s faster than a calm half

Same 180 W average, three ways to ride it

Ride harder into the wind, then ease off with it so the average still comes out at 180 W. Riders have been tested at 5% in a laboratory and models at 10% either side of the average; the larger cuts with the tailwind go beyond what was studied.

  • Steady

    Into the wind
    180 W
    With the wind
    180 W
    Against steady
    Baseline

  • 5% harder into the wind

    Into the wind
    189 W
    With the wind
    163 W9% below plan
    Against steady
    Saves 1 min 5 s

  • 10% harder into the wind

    Into the wind
    198 W
    With the wind
    149 W17% below plan
    Against steady
    Saves 1 min 55 s

What this assumes

  • A flat course ridden out and back, with a steady wind blowing straight along the road. Crosswinds, gusts, hills and drafting are not modelled.
  • Sea-level air at 15 °C, road tyres on good asphalt and a chain drivetrain. Differences are rounded to 5 seconds for legibility; the real uncertainty, mostly from the wind at rider height and your drag area, is minutes.
  • No study has tested wind-matched pacing before a run, and studies of variable-power cycling disagree about its effect on the run that follows.

Why a wind costs time even though half the ride is a tailwind

On an out-and-back course you ride the same distance into the wind as with it, but not the same time. Into the wind you are slow, so that half lasts longer; with the wind you are fast, so the help is over quickly. Time is distance divided by speed, so the slow half costs more minutes than the fast half saves, even when the wind moves your speed by about as much in each direction. Drag rising with the square of the air speed is what makes a headwind slow you down so much in the first place.

Take the example the calculator opens with: a 56 mile (90.1 km) 70.3 bike leg at a steady 180 W, 80 kg of rider and bike, on aero bars, with a 30 km/h (18.6 mph) forecast over open flat ground, which is about 18.1 km/h at rider height. Calm, the ride takes about 2 h 41 min at 33.6 km/h. Into the wind the speed drops by 10.1 km/h to 23.5 km/h, and with it the speed rises by 11.9 km/h to 45.5 km/h. Even so, the headwind half takes about 34 min 20 s longer than calm and the tailwind half gives back only about 21 min 10 s. The wind costs about 13 min 10 s in all, and 66% of the riding time is spent going into it.

The same holds on any course that comes back the way it went, including multi-lap out-and-backs, because each lap is a shorter version of the same trade. Only a point-to-point course with the wind behind you comes out ahead, and the calculator does not model that case.

The forecast is not the wind you ride in

Forecasts and weather stations report the wind 10 m above open ground, the standard exposure the World Meteorological Organization sets for wind instruments. Near the ground the surface slows the air. The calculator estimates the wind at 1 m, roughly the middle of a rider's frontal area, with the neutral logarithmic wind profile and the terrain roughness lengths in the same WMO guide. The guide uses that profile to correct an anemometer reading taken at a non-standard height to the 10 m standard; using it to estimate the wind at a rider's height is this calculator's own extension, so treat the result as an estimate. At 1 m it gives about 0.60 of the 10 m figure over open flat ground, 0.79 over a low causeway with open water upwind and 0.50 over farmland with low crops.

It is one of the biggest levers on the answer. In the example, treating the 30 km/h forecast as if it were the wind at handlebar height puts the cost at about 37 min 10 s, 2.8 times the 13 min 10 s estimate. The 1 m height is itself an assumption: evaluating the wind at 0.8 m or 1.2 m instead moves the estimate from about 11 min 30 s to 14 min 35 s.

The profile assumes a neutral atmosphere and uniform ground for a long way upwind, and in other conditions the wind near the ground can differ from it in either direction. Hedges, trees, buildings, cuttings and embankments make the wind on a particular road unpredictable, which is why the calculator offers no class for them, and gusts are stronger than the mean wind speed a forecast headline gives. If you have ridden the course in similar conditions, your own estimate entered as wind at rider height may be better than any correction.

Should you ride harder into the wind?

Coaching advice disagrees. Endurance Nation's long-course coaches have told triathletes not to raise their effort into a headwind and not to ease off with a tailwind; BikeRadar, drawing on time-trial riders, has argued the opposite. The physics favours a modest push: the same extra watt saves more seconds per kilometre where you are slow, and you spend more of the ride being slow.

Models agree. Swain (1997) modelled a 40 km time trial in alternating 5 km sections of 16 km/h headwind and tailwind, and varying effort by 10% either side of the same mean oxygen uptake saved 29 seconds. Atkinson, Peacock and Passfield (2007) reran Swain's windy course with the validated Martin road-cycling model and found 51 seconds for a 289 W rider varying power by 10%, with the lowest-power riders gaining the most.

The only study we found that had people ride it was in a laboratory. Atkinson and Brunskill (2000) put seven cyclists through a 16.1 km time trial on a Computrainer with a simulated 8.05 km/h headwind on the way out and tailwind on the way back. Riding 5% above their mean into the headwind they finished in 1659 seconds, against 1661 seconds at constant power, a gap too small to be sure of, and their overall perceived exertion and rise in blood lactate were the lowest of the three trials. In a first trial, ridden before the other two, they paced themselves, started 14% above their eventual average and finished in 1671 seconds. The authors recommended pacing a windy course by power rather than heart rate or feel.

Holding the same average after riding harder into the wind takes a bigger cut with it whenever the headwind half still lasts longer. In the example, 189 W into the wind needs 163 W with it, a cut of 9% for a 5% rise, and saves about 1 min 5 s; 198 W and 149 W, a cut of 17%, saves about 1 min 55 s. The 17% cut goes beyond the 10% either side that the models tested. Set against a wind cost of 13 min 10 s, the pacing wins back a fraction of it, not all of it.

In the one power-meter study of an Ironman we found, six well-trained triathletes on a flat, three-lap out-and-back course in a fairly steady 17 to 30 km/h wind did not raise their power into the wind: neither their power nor their speed differed significantly between headwind and tailwind sections, so the wind's effect along that course may itself have been small (Abbiss and colleagues, 2006).

What the calculator does not know

It does not know how you will feel, or how you will run. Equal average power is not necessarily equal fatigue. In the 5% laboratory trial riders rated the variable plan the easiest of the three, and when eight triathletes rode 30 minutes with swings of 5 to 15% around the same average, their knee extensors were no more fatigued than after steady riding (Lepers and colleagues, 2008). No study has tested wind-matched pacing before a run, and studies in which power varied without being matched to the wind disagree. Ten triathletes ran 5 km about 50 seconds slower after a 20 km ride that swung between 68% and 92% of their maximal aerobic power than after a steady ride (Bernard and colleagues, 2007), while eight triathletes ran longer to exhaustion after 30 minutes alternating 20% either side of a steady power (Suriano and colleagues, 2007).

It does not reward variation for its own sake. With no wind, the model says riding 10% harder for the first half and easing off for the second costs about 10 s, in line with modelling by Wells, Atkinson and Marwood (2013) that found swings in power add time over 40 km in steady conditions. The gain only exists because the wind changes from one half to the other.

It only sees wind blowing along the road. A crosswind adds drag that depends on how your wheels, frame and body behave at an angle to the air, which no single number captures, and gusty crosswinds also affect handling, which the calculator does not consider. It also assumes a flat road, a steady wind, no drafting, sea-level air at 15 °C (density 1.225 kg/m³), tyres with a rolling resistance coefficient of 0.005 and a 97.5% efficient drivetrain.

The position presets are estimates in every position. They start from one rider's static wind-tunnel drag areas for a time-trial position, the drops and sitting up (Blocken and colleagues, 2013) and add the 31% by which drag area rose between a static position and the effort position at race pace in professional riders on a time-trial bike (García-López and colleagues, 2008), so 0.211 m² becomes 0.28 m², 0.243 m² becomes 0.32 m² and 0.270 m² becomes 0.35 m². Applying that ratio to a different rider, and to road positions, is an extrapolation, and many age-group athletes are less aerodynamic than a rider tested in a wind tunnel. A drag area from your own field or tunnel testing, entered as a custom value from 0.15 to 0.6 m², will beat any preset.

Differences are rounded to 5 seconds (whole minutes once the cost passes an hour) to keep them readable, and the calm-day time to the minute. The real uncertainty, mostly from the wind at rider height and your drag area, is minutes, so compare the pacing options with each other rather than trusting any one figure to the second.

Using the numbers on race day

Decide your targets before the start. Check the forecast direction against the course map, work out which half is into the wind, and write the two power figures somewhere you will see them. Ride to power rather than speed: into a headwind your speed will look alarming, and that is expected.

If the wind blows at an angle to the road, enter the part that blows along it: about 87% of the forecast at 30 degrees, 71% at 45 degrees and 50% at 60 degrees. The crosswind part adds drag that the calculator does not estimate, so for an angled wind the cost it gives is probably on the low side.

Common questions

How much does a headwind slow you down on a bike?
It depends on your power, your position and the wind at rider height, which is usually well below the forecast. In a steady-state road-cycling power model, a rider holding 180 W on aero bars (drag area 0.28 m², 80 kg with the bike) rides at about 33.6 km/h in still air and about 23.5 km/h into an 18.1 km/h headwind at rider height, roughly what a 30 km/h forecast becomes over open flat ground. Over a 90.1 km (56 mile) out-and-back, that wind costs the same rider about 13 min 10 s at steady power.
Does a tailwind make up for a headwind?
No, not on a course that comes back the way it went. Time is distance divided by speed, so the slow headwind half costs more minutes than the fast tailwind half saves, even when the wind changes your speed by about as much each way. For a rider holding 180 W on aero bars (drag area 0.28 m², 80 kg with the bike) on a 90.1 km (56 mile) out-and-back with an 18.1 km/h wind at rider height, the headwind half loses about 34 min 20 s against calm and the tailwind half gives back only about 21 min 10 s.
Should I push harder into a headwind in a triathlon?
Possibly a little, at the same average power. Models favour it: Swain (1997) found a 29 second saving on a 40 km course of alternating 5 km sections of 16 km/h headwind and tailwind when effort varied 10% either side of the mean, and Atkinson and colleagues (2007) found 51 seconds on the same course for a 289 W rider varying power by 10%. In the only rider trial we found, a 16.1 km laboratory time trial with an 8.05 km/h simulated wind, riders who went 5% harder into the headwind were no slower than at constant power (1659 against 1661 seconds) and rated it the easiest of three trials (Atkinson and Brunskill, 2000). Holding the average usually means easing off with the tailwind by more than you added into the headwind. No study has tested wind-matched pacing before a run, and studies of variable-power cycling disagree about its effect on the run that follows.
How do I convert a forecast wind speed to wind at bike height?
Forecasts report wind at the 10 m standard height. Using the neutral logarithmic wind profile and the roughness lengths in the World Meteorological Organization's instrument guide, the wind at about 1 m is roughly 0.60 times the forecast over open flat ground, 0.79 times over a low causeway with open water upwind and 0.50 times over farmland with low crops, so a 30 km/h forecast over open ground is about 18.1 km/h at rider height. These are estimates: carrying the profile down to rider height is an extrapolation, roads lined with trees, hedges or buildings are too irregular for it, and real conditions can differ from the neutral profile in either direction.
What if the wind is blowing across the course rather than along it?
Only the part of the wind blowing along the road acts as a headwind or tailwind: about 87% of the wind speed at 30 degrees to the road, 71% at 45 degrees and 50% at 60 degrees. The crosswind part adds drag that depends on how your wheels, frame and position behave at an angle to the air, which a simple model cannot estimate, so a calculator that uses only the along-road part probably gives a low estimate of the cost for an angled wind. Gusty crosswinds also affect handling, which such a calculator does not consider.

Sources