This has been bugging me for a while, so thought I’ll write about it. I had long since  heard about bigger motorcycles having trouble managing engine heat in heavy stop-and-go city traffic, even more so with air-cooled Harley-Davidson motorcycles.

They need air moving over the cylinder cooling fins at a minimum speed of 40-50 km/h to take away all the heat generated by the massive engines. Liquid cooled engines have it much easier as most typically have a radiator fan to help with cooling when the bike is stationary or at very low speeds. While the system is much like a car, most motorcycle radiators are much smaller than cars while their engines are not, so they can only cool effectively for a while when stationary or at low speeds, before the engine starts overheating.