Why do racing cyclists shave their legs?

Answer: Bare skin has measurably less air drag

Bare skin has measurably less air drag ✓ — For decades the honest answer was tradition: smooth legs are easier to massage and easier to clean after a crash, and everyone assumed the aerodynamic gain was tiny. Then Specialized put riders in its wind tunnel in 2014, before and after shaving, and measured about 7% less drag, worth roughly 50 to 80 seconds over a 40 km time trial. Hair sticking into the airflow disturbs the thin layer of air over the skin, and at racing speed that adds up. The old habit turned out to have a real physical payoff, and the massage and wound-care reasons still stand alongside it.

Leg hair traps heat and tires the muscles — Leg hair does not insulate a moving cyclist enough to change muscle temperature, and warm muscles perform better anyway. The measurable effect of hair is on the air flowing over the skin, not on heat.

Leg hair weighs enough to slow a climb — A full set of leg hair weighs a gram or two, nothing against a 70 kg rider and bike. The gain from shaving is aerodynamic, roughly 7% less drag in wind-tunnel tests, plus easier massage and wound care.