Slower in Winter? It’s Not Your Legs

Winter slows you down through three separate mechanisms that stack. Understanding them is the
difference between a rider who panics in December and one who arrives in spring fresh and fast.

The short version, with real numbers

Here is a simple model of one rider on a flat road with no wind, holding a steady 200 W. The only thing
that changes is the temperature. Rider and bike weigh 72 kg, CdA is 0.36 m² (hands on the hoods), Crr is
0.0045, drivetrain efficiency is 97.5%, at sea level in dry air.

Between 25°C and 5°C the air is 7.2% denser. To hold 32 km/h you need about 182 W in summer and
about 194 W at 5°C, which is 11 W more for the same speed. At 40 km/h the gap grows to about 22 W
(336 W vs 358 W), because the power needed to beat the air rises with the cube of speed.

Now add what winter really looks like: a jacket, thermal tights and overshoes. If I add just 0.02 m² to CdA
and 10% to Crr, the same 200 W at 5°C gives 31.7 km/h and a 60 km time of 1:53:39. That is nearly 5
minutes slower than summer on the same legs. To hold 32 km/h in that kit you need about 206 W, 23
W more than in July.

The physics in one line

The power you must produce on the flat is the sum of air resistance, rolling resistance, and the small loss
in your drivetrain:

P = \frac{\tfrac{1}{2}\,\rho\,C_dA\,v^3 + C_{rr}\,m\,g\,v}{\eta}

Here ρ is air density, CdA is your drag area, v is speed, Crr is the rolling resistance coefficient, m is rider
plus bike mass, g is 9.81 m/s² and η is drivetrain efficiency. Cold changes two of these terms directly (ρ
goes up, Crr goes up), and winter clothing changes a third (CdA).

At 32 km/h about 84% of the power in my model goes into the air. At 40 km/h it is 89%. At 20 km/h it
falls to 67%. So the faster you ride on the flat, the more the weather taxes you, and the less it matters
on a steep climb at low speed.

What the research says

1. Cold air is a heavier air.
   A 2019 study in the Journal of Biomechanics (Beaumont and colleagues)
   combined computer fluid simulation with a power model across −10°C to 40°C. It found that the power
   needed to hold a constant speed drops as temperature rises, because aerodynamic resistance drops. A
   separate numerical analysis of freezing to scorching conditions put the change in total drag at roughly
   2.8% for every 10°C. That matches my table: 20°C of difference is about 5.6% in drag, and about 6% in
   power at 32 km/h once rolling resistance is included. Track cycling takes this seriously: engineers
   working on the London velodrome estimated that warming the air from 20°C to 25°C is worth roughly
   1.4 seconds over 4 km for a world-class pursuiter.
   
   
2. Cold tyres roll worse.
   Rolling resistance is not a constant. In a lab test series,
   bicyclerollingresistance.com found that raising tyre surface temperature from 20°C to 40°C cut rolling
   resistance by 17.6% on average. Rothhämel (2023, International Journal of Vehicle Systems Modelling
   and Testing) measured the same trend with ambient temperature: as it falls, the coefficient rises,
   especially in the range above freezing. Higher pressure lowers it, which is one reason a slightly firmer
   tyre can help on a clean, dry winter road. On wet or gritty roads, grip comes first.
   
   
3. Cold muscles make less power.
   This is the part most riders underestimate. A review by Racinais and
   Oksa (2010, Scandinavian Journal of Medicine & Science in Sports) reports that in short-duration exercise
   performance changes by around 2% to 5% for each 1°C of muscle temperature. Earlier work by Davies
   and Young (1983, Journal of Applied Physiology) showed that peak cycling power rises and falls in a
   straight line with muscle temperature: cooling the muscle by 8.4°C reduced force, while warming it by
   3.1°C sped up the contraction. A 2009 study by Racinais and colleagues found that pre-cooling the legs
   lowered sprint power, and their advice to athletes was simple: never cool the legs before a sprint.
   My reading as a coach: this third effect matters most in the first 20 to 30 minutes, on hard efforts and
   on sprints. Once you are warm and riding steady, the air and the tyres are doing most of the damage.
   That is why a winter ride often feels “flat” early and then settles.
   

Why your winter average looks worse than the model

The model above is clean. Real winter adds friction in every direction:

• Wet roads and spray raise rolling resistance beyond what dry-road lab tests show.
• Cold chain lubricant and stiffer bearings cost a few extra watts.
• Gloves, buffs and thick layers raise CdA more than my 0.02 m² if they flap.
• Stop-start riding, traffic lights and ice patches reduce your steady average.
  Add all of that up and a rider who is exactly as fit as in August can easily be 3% to 6% slower on the same
  route. That is not lost fitness. That is physics.

How I coach riders through the cold months

1- Judge fitness by power, not speed. If your watts for a given perceived effort or heart rate are
stable, your engine is stable.

2- Compare winter to winter. Use the same loop in similar temperatures, or run a fixed test
indoors where nothing else moves.

3- Warm up longer than you think. The research says muscle temperature drives power. Ten extra
minutes of easy spinning before the first hard effort is cheap insurance.

4- Dress to stay warm, not to be heavy. A close-fitting layer flaps less and costs fewer watts than a
loose, bulky one. Do not freeze to save drag, because a cold muscle costs you more than a
flapping jacket.

5- Reset your speed targets. Plan a group ride or a tour stage with a lower average speed in the
cold, and keep the effort the same.

6- Keep the base work honest. Winter is for aerobic volume and strength. Do not chase a summer
average in December and arrive in spring tired.

Honest caveats

My table is a model, not a lab test. It assumes dry air at standard pressure, no wind, steady effort, a flat
road and the same rider position. Your CdA, mass and tyres will differ, so your numbers will too. Wind,
altitude, humidity and drafting can easily outweigh any of the figures above. Use the table to
understand the direction and the rough size of the effect, and trust your own power file for the rest.

The takeaway

If you are slower in winter, check three things before you doubt your fitness: the air density, the tyres
and the temperature of your legs. Then check your power. In most cases the engine is fine and the
environment is the culprit.
Send this to the friend who is convinced they lost their form in November.
Want a winter plan that builds your base without chasing numbers that do not matter? Get in touch
about coaching at coaching.cigalacycling.com.

Sources

Engineering Sport, The heat is on for cyclists in the London velodrome

Beaumont F. et al. (2019), Aerodynamic investigation of the thermo-dependent flow structure in
the wake of a cyclist, Journal of Biomechanics 82:387–391. Abstract

Racinais S., Oksa J. (2010), Temperature and neuromuscular function, Scandinavian Journal of
Medicine & Science in Sports 20(S3):1–18. Record

Davies C.T.M., Young K. (1983), Effect of temperature on the contractile properties and muscle
power of triceps surae in humans, Journal of Applied Physiology 55(1):191–195. PubMed

Racinais S. et al. (2009), Does the diurnal increase in central temperature interact with pre-
cooling or passive warm-up of the leg?, Journal of Science and Medicine in Sport. Abstract

Rothhämel M. (2023), On rolling resistance of bicycle tyres with ambient temperature in focus,
International Journal of Vehicle Systems Modelling and Testing. Summary

bicyclerollingresistance.com, CRR at different temperatures

Matteo Cigala
Founder & Head Coach