The inch that changed tennis forever
By Rod Cross
The modern game of tennis is played at a furious pace compared with the old days when everyone used wood racquets. Just watch old film from the 1950s and you will see that the game is vastly different. Ken Rosewall and Lew Hoad barely broke into a sweat. Today’s game has players grunting and screaming on every shot, calling for the towel every third shot, and launching themselves off the court with the ferocity of their strokes. The difference is obviously due to the change from wood to graphite racquets, which happened during the late 1970s and early 1980s. Everyone concluded that graphite racquets were much stronger, lighter, and more powerful, while the players themselves somehow became taller, stronger, and fitter. How else could the game have changed so drastically?
Racquet Width, Spin, and Power
The real reason for the change is more subtle. It’s because racquets got wider. Wood racquets were always 9 inches wide and 27 inches long, so players could check the 36-inch height of the net by putting one racquet on top of another. Today’s players can’t do that. Most racquets are still 27 inches long, but they are now 10 to 12 inches wide. They are also lighter, which means they are less powerful, but it also means that players can swing them faster, which they need to do just to get back the power they lost when they became lighter.
When players started swinging their racquets faster, they noticed an interesting effect—they generated more topspin on the ball. A ball with topspin dives down more steeply into the court after it passes over the net compared with a ball without spin. Players noticed that the ball went in more easily, despite the fact that the ball was hit at about the same speed as with their old wood racquets. So they started hitting the ball even harder, which made the ball spin faster, and it still went in. Not only that, the added swing velocity wasn’t resulting in mis-hits, due to the larger sweet zone and extra inch or two of frame clearance.
So what did they do next? The extra frame clearance allowed players to start swinging upwards at the ball to get even more spin, and they rotated the racquet in their hand to a Western grip in order to swing at even steeper angles to the ball. That grip gave them problems with their backhand, so they had to grip the handle with the both hands to tilt the frame back into a vertical position. The faster they hit the ball, the faster it spun, and the faster it spun, the harder they could hit it. That’s why players today usually have both feet off the ground when they hit the ball, and it’s why they need to grunt and scream.
Players were given an inch in the 1970s and they took a mile. The ball now spins 4 or 5 times faster than it did before the 1970s. An increase in just one inch allowed an amazing increase in spin due to steeper, faster swings and a tilting of the racquet forward by up to 5 degrees, all without clipping the frame. An example will make this very clear.
Five Times the Spin
When a ball bounces off the court it acquires topspin, even if it had no spin before it hit the court. In fact, it spins faster than most players can generate themselves when they hit a topspin return. In order to return the ball with topspin, a player needs to swing the racquet both forwards and upwards and fast enough to reverse the rotation of the spinning ball. If the player doesn’t reverse the direction of the spin, then the ball will be returned with backspin—it is still spinning in the same direction but traveling in the opposite direction back over the net.
Suppose, for example, that the ball spins at 3,000 rpm (50 revolutions/sec) after it bounces off the court. That is a typical amount of spin when a ball hits the court at around 30 or 40 mph. Returned with a wood racquet, a player won’t be able to swing up at a very steep angle without clipping the frame. He will still be able to reverse the spin, but he will get only 200 rpm or so of topspin by swinging the racquet upward fairly rapidly at about 20 degrees to the horizontal. A change in spin from 3,000 rpm backwards to 200 rpm forwards is a change of 3,200 rpm, which is a relatively big change, but it is only enough to return the ball with a small amount of topspin.
Now suppose the player switches to a 10-inch-wide racquet and swings up at 30 degrees to the ball. The player can do that and can also tilt the racquet head forward by about 5 degrees, with even less risk of clipping the frame than with a 9-inch-wide wood racquet being swung at 20 degrees with the head perpendicular to the ground. In this way, the player will be able to change the spin by about 4,000 rpm instead of 3,200 rpm, with the result that the spin changes from 3,000 rpm of backspin to 1,000 rpm of topspin. The result is therefore a factor of five increase, from 200 rpm to 1,000 rpm, in the amount of topspin. That’s an amazingly big effect considering that the racquet increased in width by only one inch, or by only 11 percent.
Why Width Matters
A 9-inch-wide racquet swung with the strings in a vertical plane has about 8 inches of string in the vertical direction and about one-half inch of wood above and below the strings. A 10-inch racquet swung in the same way has about 9 inches of string in the vertical direction. The ball is just over two and one-half inches in diameter, so 3.1 balls can fit across a 9-inch racquet and 3.5 balls can fit across a 10-inch racquet. If the 10-inch racquet is tilted forward 27 degrees, then the strings extend 9 inches diagonally and 8 inches vertically, as shown in Figure 1. The racquet can therefore be swung upwards at 27 degrees or tilted forward by 27 degrees, and it will then present to the ball exactly the same area of string as a 9-inch racquet. No one tilts the racquet forward by as much as 27 degrees, but they now swing up into the ball at angles of 30 degrees or more to generate topspin. Tilting the racquet head forward slightly generates even more topspin.
Giving a player an extra inch of width allows the player to swing up at a steeper angle or faster or both. In that case the ball slides farther across the strings, so you really do need that extra inch. A change in 4,000 rpm rather than 3,200 rpm is therefore not surprising given the extra speed, angle, and tilt made possible by the extra one inch of width.
Going from a 10-inch to an 11-inch racquet does not deliver another huge increase in topspin. The reason is that if players tried to increase the upward speed of the racquet any more than they do now, the ball would sail over the baseline. They can do that for a topspin lob, but the forward speed of the racquet and the ball remains relatively small for a topspin lob. An 11-inch racquet will work better for topspin lobs but not for any other shot. On the other hand, 9-inch racquets were only just over the limit of being able to generate any topspin at all. Give a 9-inch graphite racquet to a player today and the result would be some serious clipping of the frame every few shots, though perhaps not as many as “old-timers” might expect because modern players are so practiced and skilled at steeper swings.
Further details are described in the new book Technical Tennis: Racquets, Strings, Balls, Courts, Spin, and Bounce, by Rod Cross and Crawford Lindsey, available from book store web sites or from the publisher at usrsa.com.
See all articles by Rod Cross
About the Author
Rod Cross retired in 2003 as an honorary member of the Sydney University staff and continues to work on the physics of sport and forensic physics. He is a physicist and co-author of The Physics and Technology of Tennis available from the USRSA.