Generic "feels like" apps ignore humidity. WBGT — wet-bulb globe temperature — is what military and pro-team staff use to set pace limits in the heat, because it accounts for sun, wind, humidity and temperature. We use both the wind-chill index (for cold) and a WBGT-style score (for hot) and translate each into clothing and pacing recommendations.
The standard wind-chill index is correct for cold, dry conditions and a steady rider — but the moment humidity climbs, it stops telling the whole story. A 30 °C day with 80% humidity is physiologically harder than 30 °C with 30% humidity, even at the same "feels like" temperature, because sweat can't evaporate.
WBGT (wet-bulb globe temperature) accounts for sun, wind, humidity and temperature in a single number. Above WBGT 27 °C, sustained heavy exercise becomes risky for unacclimatized riders. Above 30 °C WBGT, even acclimatized riders should consider a pace limit or shortened ride.
Standard apps use heat index (temperature + humidity only). WBGT includes sun and wind, so it tends to be more cautious in direct sun or low wind. For sustained outdoor exercise, WBGT is the better guideline.
Wind chill matters most for exposed skin — face, fingers, toes. If you're covered up, your body feels the actual air temperature, not the wind chill. We use chill for skin-warning timing, but the rest of the recommendation is based on real air temp.
WBGT variants are used by race organisers as part of heat-stress protocols. The UCI's 2023 extreme-weather protocol uses a wet-bulb thermometer reading.
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