| Ball aerodynamics |
 | | Wind tunnel (front) |  | | Wind tunnel (rear) |
Since 2001, the ITF has been conducting wind tunnel tests to measure the aerodynamic characteristics of tennis balls. The ITF wind tunnel is similar to those used by Formula 1 teams when designing and redefining the shape of race cars. Purpose built to hold objects about the size of a tennis ball, the wind tunnel can generate wind speeds of up to 160 mph, using a 25 hp (19 kW) fan. Air is sucked in at the front end and passes through a series of filters before reaching the working chamber, which houses the ball. Curved diverter panels help to cycle the air around the sound proofed room as it exits the exhaust.
As spin has considerable effect on the ball's trajectory through the air, the tunnel has the unique facility of being able to generate spin on the ball. Load cells measure the forces that the ball experiences as it "flies through the air." The first of these is the force in the horizontal direction, which tends to slow the ball down and is known as drag. The seconds acts in the vertical direction, and tends to either keep the ball in the air or return it to the ground, depending on whether it has topspin or backspin.
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