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Outlook 2005: String

Research into strings and stringing are leading to a whole new understanding of their effects on play.

By Crawford Lindsey

Research in the string field in the last several years has revealed some perplexing, contrary-to-expectation conclusions that are leading to a new understanding of racquet strings and, possibly, a new vocabulary to go along with it. What are some of these research conclusions? Most have to do with the role of tension in string performance, and many cause more questions than answers.

Tension and Power

Perhaps the most startling revelation is how altering string tension affects power (ball velocity). The old adage “string loose for power, tight for control” still holds, just not to the extent that we previously thought (i.e., looser strings will not change power by 20 percent, 10 percent, or even 5 percent).

If you drop string tension by 10 pounds, the percentage gain in ball velocity will be less than 1 percent (about .7 percent), or about .4 mph on a 60 mph ground stroke. That is certainly not significant enough that you can feel the difference in the ball leaving your racquet or see during its flight. But it can add several inches to the depth of your shot, which is significant depending on your usual consistency level and when viewed over the long-term of an entire match.

The ball travels farther for two reasons. First, it actually is traveling a bit faster, so it will land deeper. Second, because the ball stays on the racquet longer with looser strings, the player will swing through a larger arc during this time and the ball will, therefore, take off at a higher angle and travel farther. So the increased depth is due to both an increased launch speed and angle.

If we can’t see or feel the power difference during the hit, but only infer it by where the ball lands, and if the increased depth is due to speed and angle, perhaps the old adage should be revised to “string loose for depth and tight for safety.”

Tension and Spin

Another old adage says, “String tight for spin.” Lab tests at the University of Sheffield, England, have shown that string tension has virtually no effect on spin. Yet players insist they get more spin. What gives? The answer is probably two-fold.

First, because tighter strings produce less depth, the player swings harder to get the depth back. A faster swing will then produce more spin. The second explanation is based on an illusion of more spin. If the ball is leaving the racquet slower (i.e., assuming the player does not compensate with a faster swing) with tight strings but with the same spin, the spin-to-speed ratio will be greater, and the ball will bounce as if it has more spin. So, tight strings do not in themselves cause more spin, but they might cause the player to create more spin. The adage might thus be rewritten to read, “String tight if YOU want to add more spin.”

Tension and Stringing

But what does stringing tight or loose really mean? What you feel when the ball hits the strings is the consequence of the stringbed stiffness. Every string material, construction, gauge, and tension, as well as every racquet head size and string-pattern density contribute to stringbed stiffness. But all that most players ask for when they go for a restringing is a particular tension.

The tension is the closest thing to a universally used indicator and prescription of stringbed feel. That is fine if you use the same string in the same racquet. But tension in itself is not a common denominator between different racquets and strings. Stringbed stiffness is, however.

A stringbed stiffness reading that is the same in two different racquets with different strings should make the racquets feel very similar; two different size racquets at the same tension would not. Knowledgeable stringers can compensate by adjusting tension to make racquets feel similar, but wouldn’t it be easier if there was a universal comparative such that a player would come to know what value they like, regardless of the racquet or string being used?

There are two problems with establishing a universal stringbed standard — one logistical and one technical. The logistical problem is that stringbed diagnostic machines are expensive and not widespread. The second problem is that a stringer could never consistently combine all the variables listed above to satisfy the new customer who comes in with a new racquet and new string saying, “String this up to a 70 (a typical RDC diagnostic machine reading) stringbed stiffness.”

Tension and Player Perceptiveness

Virtually all players assume that they can tell the difference between different tensions. Some claim to be able to identify a difference of a pound or two. Tests have been performed (Professors Rod Cross and Rob Bower) that bring that claim into question. In a test of 41 advanced recreational players, only 11 (27 percent) could determine a difference of 11 pounds or less. In fact, 15 (37 percent) couldn’t correctly identify the difference even when the tension between two racquets varied by 22 pounds.

Using earplugs to dampen auditory clues lowered the success rates even more. Players were only allowed four hits with each racquet, so the only data the player was interpreting was feel, not an accumulated history of location of ball placement that could be used to deduce string tension. Some players said that they noticed a difference, but then incorrectly chose which racquet had a higher tension.

Conclusion

These findings, of course, bring into question what players really feel or think they feel and how they describe what they feel. If they can’t properly differentiate the feel of power, spin, and tension, what do they feel?

What is actually felt is the shock and vibration of the handle hitting the hand. This sensation is made up of the rotation, translation, and bending of the racquet.

You don’t actually feel the strings, but rather you feel how they alter the duration and amplitude of the thump and buzz of shock and vibration. The brain has to analyze this information and turn it into the vocabulary of “feel.” As such, it is an interpretation, not a raw feel. And there is not enough information in this impact feel alone to produce the rich vocabulary that players use to describe the sensation — crisp, dead, grabby, clean, springy — nor is there enough information to determine the amount of power or spin.

The natural conclusion is that players “experience” the string; they don’t just feel it. This is a holistic experience that includes feel, sight, sound, intellectual interpretation based on the placement results of many shots, and how the player knowingly or unknowingly alters his stroke as a result of those shot results. The interpretation then becomes the lens through which a player describes his “feeling.” And then, the player attributes the cause of this post-facto interpretively constructed “feeling” as a characteristic of the strings — “these strings have a lot of bite.” It’s a convoluted web we weave.

However, there is no denying that string materials, tensions, gauge, etc. alter the performance outcome of a racquet and the player. Future string research will help clarify these phenomena and help us talk about them, but in the meantime, we will simply have to interpret each other’s string babble. After all, we all know what we mean … right?

See all articles by Crawford Lindsey

About the Author

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

From the February 2005 issue
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