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 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.

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.