Soft, greasy tarmac
In a heatwave, road surfaces get much hotter than the air — far above 50 °C in direct sun. The bitumen that binds the surface softens and bleeds to the top, leaving shiny, greasy patches. They collect where traffic stands and brakes: junctions, roundabouts and the approach to lights.
Tyres run too hot go greasy rather than sticky. Combined with bleeding tarmac, a very hot day can offer less grip than a mild one.
Heat and the rider
Dehydration and heat exhaustion slow your reactions long before you feel unwell. Drink before you are thirsty, stop in the shade, and keep your kit on — asphalt at speed is no place for bare skin. A vented jacket and an evaporative vest go a long way.
Riding early or late avoids the worst of it: the road surface is coolest in the morning.
How RideWindow scores heat
The ride score's temperature points fall away quickly above your comfortable range (up to 32 °C by default, adjustable in a rider profile), and the grip estimate separately prices very hot tarmac and air. The ride windows will lean toward the cooler morning and evening hours on a hot day. Check your area or a city or pass.