How hot is too hot to ride a motorcycle?

Why the wind stops helping

Moving air cools you in two ways: it carries heat off skin that is warmer than the air, and it dries your sweat. Skin usually sits around 35 °C (95 °F), and when the air is hotter than your skin, your body picks up heat from it by convection, even though moving air still helps sweat evaporate. So the closer the air gets to skin temperature, the less the wind cools you; once the air is hotter, the wind can add heat instead. From there, evaporating sweat is your main way to shed heat, and how well that works depends on humidity, how much you drink and how freely your gear lets sweat out. Airflow may still help by drying sweat faster, which is why 35 °C is where one way of losing heat flips, not a line above which nobody should ride. Public-health advice on fans follows the same logic: the CDC says that indoors, above 90 °F, a fan can raise your body temperature, and on a motorcycle the wind plays the fan’s part.

The heat index, and the sun on top

Humidity decides how much sweat can still cool you. The US National Weather Service heat index combines air temperature and humidity into one figure and sorts it into four classes, from Caution at 80 °F to Extreme Danger at 125 °F. Dry air lets sweat evaporate, so at the same temperature a dry day reads lower than a humid one; at 35 °C (95 °F) the index is about 33 °C (91 °F) in dry air and 37 °C (99 °F) at moderate humidity. The index assumes shade, and direct sun can add up to 15 °F, about 8 °C. A rider on a hot road is rarely in the shade, which is why the calculator gives the shade figure and reminds you the sun comes on top.

What heat does to a rider, and what helps

In a 2019 laboratory study, volunteers wearing motorcycle protective clothing pedalled lightly for 90 minutes at 35 °C (95 °F) and 40 % humidity, under radiant heaters and a fan simulating wind. Their core temperature rose by about 2 °C (3.6 °F), their reaction times fluctuated by 36 ms (8 %), and they reported feeling less alert. The authors note that many riders leave their protective gear at home in the heat, and that much of the gear on sale copes poorly with it; they call on manufacturers to make gear that works when it’s hot.

What helps is ordinary hot-weather sense, not something that study tested: vented gear, water at every stop, shade breaks, and riding early or late in the day.

Cold instead? The same calculator runs down to −10 °C on our guide to how cold is too cold to ride.

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