Tennis Industry magazine


String Selector Map 2007: String it up!

Whether your customers realize it or not, their games depend not only on the string they choose, but also on how often they restring.

By Crawford Lindsey

Our String Selector lists nearly 600 strings, which can easily make you want to throw up your hands in despair. Given all these choices, selecting a string is a daunting task. To make things even more complicated for your customers, deciding when to restring can be confusing, too.

When to restring depends on your choice of string to begin with. So let’s look at the interplay of string selected, frequency of restringing, and performance.

When Should You Restring?

Touring pros restring every day. Recreational players restring anywhere from every three or four times they play to once a decade, or until the strings break. But the pros’ frequent restringing tells us something: String — especially fresh string — matters a lot. Why? What possible difference could restringing your racquet every day make?

Tennis string has an unfortunate property — beginning from the very second it is put into the racquet, it loses tension. A racquet strung at 60 pounds will most likely be at 50 pounds the next day, and tension continues to decline with every second and with every hit. Tension loss is the only physically significant process impacting your tennis racquet (and string wear). This is why racquets need to be restrung.

You probably have customers who will say, “Heck, I don’t even pay attention to what tension it gets strung at in the first place.” Well, they need to consider what tension loss does to racquet performance.

More power, less control, change in stroke.

As tension goes down, the strings stretch more upon impact. This cushions the ball’s landing, minimizing the squashing effect. When the ball flattens, it loses a lot of energy. So less squashing means more energy for rebound. The strings always return almost all the energy that goes into stretching them, whatever the tension. So power is all about what happens to the ball, not what happens to the strings.

Power is good if you want it, can control it, and know how much to expect from day to day. That is how you groove your stroke — by responding the same way to the same situation. But your strings deliver varying amounts of power from day to day and from hit to hit. This works against “grooving” anything. As you struggle to keep the ball in, you constantly change your stroke.

More dwell time, less control, change in stroke

When the strings stretch more, the ball stays on the strings longer. The increase is only a millisecond or two (depending on where on the racquet you hit and how violent the impact, dwell time is typically 5 to 7 milliseconds). But, surprisingly, during that extra millisecond, your racquet will sweep through both a larger vertical and horizontal arc. This will launch the ball on a higher and more sideways trajectory than you are used to. The ball goes long and wide. This coupled with more ball speed from less ball squashing is a double whammy. You can’t figure out what technical flaw has emerged in your stroke, and you begin to mess with perfectly good mechanics to fix your mysterious ailment.

Change in feel, feedback, and stroke

As strings lose tension, you may feel that the racquet is “going dead,” “getting mushy,” or “losing its punch.” Obviously it is not, since the ball is going faster and farther. But what is happening is you have lost the “crisp” feel you have become accustomed to. “Crisp” of course means more shock, but shock is feel. The only sensations of striking a ball that your hand feels are shock and vibration. This is your feedback mechanism. When the feel is the same every time, your response is to groove the stroke; when it is different, you respond by continually adapting and adjusting your stroke.

The other feedback that changes is auditory. The sound the strings make changes. As tension goes down, hitting the ball goes from a “ping” to a “thud.” Players may interpret these sounds differently as to what they mean about the “cleanness” of their hits, and when this sound changes, so does the player’s psychology. It affects what they think they are doing, how they are performing, what the results are, and whether they are in “the zone” or not. All this affects the mental and physical approach to the next shot.

Change in spin and stroke

It has been shown that string tension has very little impact on spin. A ball fired obliquely at the same racquet with different tensions rebounds at about the same spin. However, if tension goes down and you are thus hitting the ball deeper (too deep), your natural response will be to either hit it more softly or to add more spin. The loose strings don’t cause more spin; rather, they cause you to add more spin. Again, these are usually unconscious adjustments to your strokes as your day-to-day racquet performance changes. Your strings change your strokes daily. And you thought you were just having a bad day.

More string movement, less durability, less performance

Strings slide across each other more easily at lower tensions. The main strings move back and forth over the crosses. This has a couple of obvious effects. First, it shortens the life of the strings as they saw through each other. Second, if you don’t move the strings back into place after each hit, you will have an uneven string pattern and will end up with an uneven power and control response across the string face. This will affect the bounce of the ball and you will be making stroke adjustments to compensate.

Consistency is Key

I could go on, but you get the idea. If you don’t restring often enough, chances are you’ll spend much of your tennis life compensating for your changing string tension instead of honing your swing. “Consistency” is the key. You want to play with the same racquet as you did yesterday — one that will behave the same way in the same situations, so you can let your muscle memory take care of swinging while you figure out what you’ve got to do to beat the guy on the other side of the net.

So, how often should a customer restring? If they’re a frequent player, the answer is most probably, “More often than you do now!” I’ll bet that for most of the recreational playing population, doubling their restringing frequency from what it is now would not be overkill.

More objectively, a good guide is to restring when the stringbed stiffness (measured by equipment in your pro shop) has dropped by 20 percent from the reading immediately after stringing. Your customer will have to experiment to find what works and feels best to them.

In the end, though, I think your customer will find that this is definitely a case where more is better.

Test Procedure

Each string was tensioned to 62 pounds and allowed to sit for 200 seconds. Then the string was hit five times with a force equivalent to hitting a 120 mph serve. The tension loss represents the total amount of the relaxation over both time and impact. The stiffness value is a calculation derived from the amount of force created at impact to stretch the string. Lower values represent softer strings and lower impact forces. Higher values represent stiffer strings and higher impact forces.

The Geography of ‘Feel’

Finding Your “Feel Good” Location

Refer to the “maps” that show tension loss vs. stiffness for each string. There is one overall map, and individual maps for each of the four major string types (nylon, poly, gut, aramid).

Hybrids: to look up a hybrid combination, you must look up each string separately. If it is a pre-packaged hybrid, most packaging indicates the name of each string. Here is a listing of hybrid combinations.

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About the Author

Crawford Lindsey  is co-author of The Physics and Technology of Tennis and Technical Tennis



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