Experimental Results

Results of measuring balance point and swing weight for over 200 different racquets are shown below. The racquets were tested by the US Racquet Stringers Association who kindly provided me with their results. Note that all light racquets are head heavy and all heavy racquets are head light. If a heavy racquet was constructed like a baseball bat or like a golf club with most of its weight in the head then it would be very powerful but difficult to swing using only one hand and difficult to control. The only way around this problem, using a head-heavy racquet, is to make the racquet relatively light so it is easier to swing and easier to control.

The power built into a racquet by the manufacturer, using various tricks to distribute the weight and stiffness, can be measured in terms of its ACOR. The ACOR varies over the string plane. Results for 268 different racquets at a point 16 cm from the tip (near the middle of the strings) are shown in the two graphs below. In general, heavy racquets tend to be more powerful than light racquets, assuming that all racquets are swung at the same speed. Most of the time, players swing their racquets at a medium speed, not as fast as they can.

The second graph shows that the ACOR depends primarily on swing weight and racquet length. All racquets of the same length and the same swingweight, at the same stringbed stiffness, will have the same ACOR in the middle of the strings and will therefore be equally powerful. Stiff racquets will be more powerful than flexible racquets near the tip since less energy will be lost in frame vibrations. But they are equally powerful at the sweet spot (ie the vibration node) near the middle of the strings.

ACOR contours for two different racquets are shown below. The Prince Viper racquet is a particularly stiff racquet so the ACOR near the tip is relatively high, despite it being a relatively light racquet. The ball bounces best near the throat region of a racquet and worst near the tip and around the frame of a racquet. Measurements close to the frame cannot be made since the ball would hit the frame at such impact points. ACOR contours are NOT concentric circles as often shown in advertising brochures. The ball speed off a moving racquet depends on both the ACOR and the speed of the racquet. Since the tip travels faster than the throat, the outgoing ball speed is a maximum for an impact point that depends on (a) the ACOR contours (b) the speed of the incoming ball and (c) the speed of the racquet. The ACOR contours here represent outgoing ball speed divided by incoming ball speed for a case where the racquet speed is initially zero.