Cycling creates wind even on a still day. At 20 km/h, you're generating a constant breeze on your legs that an air temperature reading doesn't account for. This matters for shorts decisions.
Wind chill while cycling
Wind chill depends on both air temperature and wind speed. On a bike you add your cycling speed to any actual wind speed. Cycling at 18 km/h into a headwind of 15 km/h means your legs experience 33 km/h of wind.
At 16°C air temperature with 30 km/h effective wind, the wind chill drops to approximately 11°C on exposed skin. That's cold for bare legs over a longer ride.
| Cycling speed | Air temp | Effective feels-like |
|---|---|---|
| 15 km/h, no headwind | 18°C | ~15°C |
| 20 km/h, no headwind | 18°C | ~14°C |
| 20 km/h, 15 km/h headwind | 18°C | ~11°C |
| 25 km/h, 10 km/h headwind | 20°C | ~14°C |
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The rule of thumb for cycling
Add 5–8°C to your minimum shorts threshold when cycling. If you normally wear shorts from 18°C, think 23–25°C for comfortable cycling in shorts. Or bring leg warmers for the first part of the ride and take them off once you're warmed up.
Stopping vs moving
The other factor is stops. Cycling generates body heat that compensates for wind. The moment you stop at traffic lights or a café, that heat production stops but the cold air doesn't. After a longer stop in shorts at 16°C, getting back on the bike takes a few minutes to warm up again.