Join Date: Mar 2010
Location: Southern California
Strings and Spin: Applying What We Know About Copoly
by Joshua Speckman
So can anything be done to keep the main strings sliding and snapping back longer?
Well, on clay courts, it might make sense to rotate rackets more frequently than normal during a match to minimize accelerated friction-wear from the dirt, and then wipe accumulated clay off the strings before playing again.
Rotating rackets more frequently may be important for copoly players.
Fischer notes that plastics like copoly will also melt and notch due to heat from friction. So in practice sessions, where a player might hit many more balls in an hour than in an entire match, it might not be a crazy idea to again rotate rackets frequently to keep the strings from over-heating.
Although it is not widely available outside of Japan, the silicone-based lubricant called Mira-fit may also prolong or revive the snapback ability of worn and notched strings. In a recent experiment, Crawford Lindsey showed that the commonly available lubricant WD-40 both revives the spin potential of notched strings and improves the spin generated by new strings as well. And it should also reduce premature wear by reducing friction and heat. These lubricants are currently legal for tournament play.
Another factor to consider is thickness, or gauge. Traditionally, thin, high-gauge strings have been favored for feel and spin. But the old explanation - that the strings allowed the ball to bite deeper into the pattern, increasing friction - doesn't square with what science is telling us about strings and spin.
But once the link was made between slippery copoly and spaghetti strings, researchers began wondering how copoly strings could be freed to move with less friction and more freedom within the constraints of a woven stringbed. "Thick strings are maybe less slippery, because thick strings, when you weave them there's a bigger angle to the weave," says Cross.
"But if they were only one micron thick there would be hardly any distortion of the strings and they would slide sideways and come straight back." At the other extreme, he says, "if they were a half-inch thick they would be really locked in together."
At present there is, however, no objective evidence that thinner strings do give more spin. Players routinely report that they do, but determining whether they are correct will have to wait for more research.
Finally, what about the great variety of shaped or textured copolys on the market – all advertised as spin strings? Well, according to tennis scientists, because the stringbed is woven, with natural peaks and valleys, all strings have sufficient friction with the ball at most impact angles to generate spin. So, theoretically, any additional friction provided by rough or pentagonal strings shouldn't make any difference.
But subjective reports consistently contradict this. At one online string playtest database, 17 of the top 20 strings rated by players for spin were shaped or textured copolys. Remember, scientists originally dismissed the existence of the poly-spin effect, despite how obvious it was to the players. So perhaps it is a mistake to discount their perceptions again.
So what's going on here? Science is always a work in progress, and this is one area where more research needs to be done.
But so far, there are two possible explanations. First, Crawford Lindsey says that increased friction between the textured strings and the ball may play a role during the snapback phase.
We know that the ball must grip the main strings in order to slide and stretch them sideways. But once the main strings reverse direction and start snapping back, they have to re-grip the ball in order to apply spin-enhancing torque. If the strings can re-grip the ball quicker they can apply spin-enhancing torque for a slightly longer period of time. So it might be during the snapback phase that textured and shaped strings have an advantage.
However, Lindsey's recent experiments showed that lubricating strings increased the spin potential, across the range of string materials. A lubricant will reduce friction between strings, but also between the ball and the strings. So whatever role string-ball friction may have in spin generation, it is almost certainly less important than having the intersections between strings as slippery as possible.
Still, there is one scenario where a player would want the highest possible string-on-ball friction. On almost all shots, theory and lab tests agree that slippery strings, and rough or textured strings, both have plenty of friction to spin the ball.
But on extremely steep swings with the racquet moving very fast – a topspin lob or the heaviest Nadal forehands being good examples - the ball can actually slip off the strings instead of biting them. In this case, a really rough string produces more spin than a really slippery one.
In any case, it's important to note that greater friction generally only makes a difference in the interaction between the ball and the main strings. This is because it is the main strings that are gripping the ball, sliding and snapping back. The role of cross strings in the snapback mechanism is to act as stiff and slippery rails for the mains to glide and slide on.
So one way to possibly have your cake and eat it too is to use a smooth and slippery cross string paired with a slippery but textured main string, something that string manufacturers have realized. Several manufacturers now offer hybrid packages containing two half-sets: a textured copoly for the mains and a smooth copoly for the crosses.
But regardless of the potential of copoly strings, the big question is still: Is this stuff for everyone? For players who hit flat, don't break strings, have tender elbows, or feel they need more pop, natural gut remains the gold standard.
And according to Cross and Lindsey's tests, gut is pretty good at generating spin too: offering about 15% more than nylon. Gut remains popular on the WTA tour, where power and spin may be more valuable than spin alone. The Williams' sisters, along with Justine Henin (up until her 2nd retirement), continue to use gut, the string favored by pros for over a hundred years.
Syngut and multifilament strings, both made of nylon, don't spin the ball as well as copoly or gut. They are softer and more arm-friendly than copoly, but less powerful than natural gut. Many of them are also pretty cheap, and perfectly adequate for most recreational players. The biggest problem with them is that they must be straightened constantly.
And if spin isn't a huge feature of your game, does poly have any use? Quite possibly. For a player with conservative grips and/or traditional mechanics, an experiment with copoly might be worth a try, as the strings will give you more spin with the same swing and effort.
Nate Ferguson says that Pete Sampras, with his relatively flat, classical strokes, switched to Babolat RPM Blast last year and is enjoying the greater "spin control" on the senior tour.
One final thing to note is that lab results will not always be consistent with our on-court perceptions. Because each different string setup will launch the ball at a slightly different angle, and with slightly more or less speed than others, its very difficult to subjectively evaluate how much spin we're getting out in the real world.
Applying lubricant to strings is an extreme example of this. We know from lab tests that lubricant will increase spin considerably. But it will also raise the launch angle quite a bit as well. Consequently, out on the court we may find the ball going long, even with all the extra topspin we're getting. To compensate, we could flatten our swing slightly to lower the launch angle, but this will reduce the spin. Alternatively, we could close the racquet face slightly at impact. This will also lower the launch angle, but increase the spin.
We can adjust to a new string setup in different ways, but unless we know exactly which adjustments we're making it's very difficult to distinguish what we're doing from what the strings are doing.
Lab research is invaluable because it reveals what is really happening. But it's also limited because the player isn't in the lab. On-court results will always be the most important dataset in tennis.
Scientific research into strings has really raised our understanding of why some strings generate more spin than others. But as always, more knowledge leads to more questions. Crawford Lindsey and Rod Cross soon plan to answer some of them by comparing the spin potential of many more strings and combinations in direct head-to-head tests.
But for the individual player, at this point there are no simple prescriptions. Level, playing style, injury—not to mention the patience and cost involved in conducting your own experiments to chose the right string or string combo—all need to be considered when choosing which strings are right for you.
But one fact is indisputable. The copoly effect is real. And the practical applications of the slippery string theory will continue to be refined and evolve as researchers, manufacturers—and players--experiment with more and more variations.
Want to Investigate More About Strings Yourself?
Crawford Lindsey, aka "The Professor", has published the most through, useful and up-to-date collection of scientific papers on strings and spin available. For those who want to learn more about the subject, or about other aspects of tennis equipment, there's no better resource.
C. Lindsey's Tennis Warehouse University
Lindsey's groundbreaking experiments on strings and spin:
"What Strings Generate the Most Spin?"
"Spin and String Pattern"
"String Friction Database"
"Spin and String Stiffness"
"String Lubrication & Movement in Spin"
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