Tennis Strings On the Court

Life Member and Treasurer David Booth sent me an article by Tennis Warehouse about tennis strings, knowing I would not be able to resist commenting. How fussy are you about your strings?

Professor Brody, who passed away in 2015, was regarded as the world’s foremost physicist of tennis. He wrote a classic book in 1987 titled “Tennis Science for Tennis Players”, chapter one of which deals with strings. From there comes the adage that tighter strings give you more control while looser strings give you more power. The general explanation is the trampoline effect: looser strings deflect more, thereby giving more energy to the ball as they return to their initial position. The loss of accuracy comes about because the ball is on the strings for longer, and unless you can keep the racquet perfectly straight throughout contact, the longer the contact period the harder to control the direction of the ball.

Does this mean if we want more power we should increase the tension?

Surely a pertinent question is how much more power will I get? In more recent years, many more experiments with tennis strings have taken place in physics laboratories around the world (including by Dr Rod Cross from the University of Sydney). It turns out that the extra power that will be gained with even a large increase in string tension is less than 1 percent!

You will not suddenly overpower your opponent if you increase your string tension! A 120 km/h ball will become a 121 km/h ball at best.

Although I cannot remember where I read it, nor the reason why, one noticeable effect of lowering string tension is to cause the ball to leave the racquet at a higher angle of elevation. Since hitting a ball higher will cause it to go further, a player might infer that they are hitting the ball harder because they observe it travelling further.

Another noticeable effect of string tension is the sound the strings make: the higher the tension, the higher pitched the “ping” produced when striking the ball. Tests have shown that most players, if they are deprived of this audible feedback, are unable to tell the difference in strings that are strung 5 pounds apart.

This raises a very interesting point: most people will claim that they really can feel the difference in small changes in string tension. I believe there are (at least) two aspects to this. The first is, we really do associate differences with different objects: if we believe a change has been made, we will feel something different; humans are not machines. The issue is whether that feeling is consistent over time, and whether it accords with any physical difference. Another aspect is self-confidence: just like most people think they have above average intelligence (the illusory superiority bias in the field of social psychology), most people will be inclined to think they can reliably feel changes to strings.

How a string feels will depend on where you hit the ball: an off-centre hit will not feel as nice. And people tend to make up their minds very quickly: studies have shown that in a fraction of a second of meeting someone new for the first time, you have already formed an impression of their personality. (If you are interested, listen to the First impressions: the face bias podcast.) Personally, I suspect the same thing happens when you test out a new racquet or new strings: if you happen to hit the centre of the strings with the first ball you will think the racquet and strings are wonderful, but otherwise, you might decide they are horrible! Or, if someone you trust has told you their opinion, you might be swayed by them (after hitting a few more balls).

Let’s return to the topic of string tension. There is something I find quite ironical. If string tension accurate to a fraction of a pound really matters, the effects would be seen by the professionals. You will have noticed tennis players use freshly strung racquets in matches. Moreover, Federer changes to a freshly strung racquet each time the balls are changed during a match. To emphasise, these strings have not hit a single ball prior to being used in the match.

But string loses a lot of tension over the first 100 hits of the ball! And string loses a lot of tension in the first hour it is in the racquet. In other words, the actual tension Federer uses is not constant throughout a match — but we do not see his form oscillating from good to bad in synchrony with his strings changing tension. Clearly, he adapts to the changing tension, just as players must adapt to the new balls. Referring to this article (whose premise I’m not sure I agree with), they explain how they measured that string can lose as much as 20 pounds in 20 hits. (There are papers in the scientific literature which have also measured string loss as a function of time and number of hits.)

Being aware of all of the above, I have experimented myself with strings. At one stage, I had three racquets strung with three completely different strings: one had a poly, one a nylon, and one a hybrid. Of course they all “felt” different. Importantly though, when I was absorbed in playing points, I was able to play with all of them just fine (and change from one to the other). Over short periods of time, balls lose their pressure and the wind changes; over longer periods, the density of air changes. Then when you change courts the bounce will change. There are so many factors that the only reason we can hit the ball in is that humans use feedback control: we hit one ball, see where it lands, then we adjust our next shot. And the only reason this breaks down is mental: demons in our head telling us that because we missed, it must be the fault of our racquet or strings. (Note that the feedback I refer to is not instantaneous feedback allowing us to correct our shot as our strings come into contact with the ball: this has been proven to be impossible given the short amount of time the ball is on the strings.)

The mental side is important. In fact, it is probably the most important. When I was young, a tennis coach told me that many people thought that it was not possible to be good at two racquet sports but that this was simply a mental block: indeed, he was both a talented tennis player and a talented squash player. Later, I became friends with a champion badminton player: he said you should be able to pick up any racquet and win a match. And I got to see that first hand, when years after he had stopped training, he picked up someone else’s racquet, and played a friendly match against the then number one player in Australia and won!

Returning to my own experimentations with string, I remember one day playing points on clay. I was not playing my best when I broke my string, changed to an identical racquet but different string, and suddenly played extremely well! Is that the string?!! No, it is not. It was simply because my mind went from having negative thoughts (“I am not playing well”) to being distracted with thoughts of “is there any difference with these new strings”?

To play well, you must stop your conscious mind from interfering with your subconscious mind. Your subconscious mind knows how to hit the tennis ball. But as soon as your conscious mind tries to override it, disaster happens. Therefore, you must believe in your strings. And there are two ways of doing this. Either you can go to great lengths to try to find the best string, and thereby gain confidence by believing you have found the best. Or you can honestly believe it makes little difference and just go with what is convenient: how much does it cost, how long does it last, and is it comfortable?

So what do I personally use? I have five Wilson racquets, three are new while two are the older model of the same racquet. And I have Yonex Poly Tour Spin in the new racquets, and at the moment, Solinco Hyper-G in the older racquets; having bought various strings in the past to experiment with, I now use the excess string in my older racquets. And although psychologically I prefer the newer racquets, there have been times when I’ve started a match with my older racquets without realising and it has made no difference whatsoever.

Jonathan Manton
05 Nov 2018

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