WIND TUNNELS 101

FANS

Air is powered up to speed by big fans. The Specialized tunnel has six 6ft fans, each with a 75bhp motor. The fans are placed behind the test area and blow the air around the duct

DUCT

Carries the air to and from the test area

BALANCE

Electronically measures drag, usually with sensitive strain gauges and the test subject ixed. Bike balances include a drum under the rear wheel with a heavy ly wheel linked to the front wheel so both can spin

YAW ANGLE

The wind angle seen by the rider; a product of the rider’s forward speed and any crosswind. A 40kph bike speed and a 40kph crosswind hitting the bike at a 90° angle would give a yaw angle of 45°, though more than 20° is rare in cycling