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PEEK, Polyester, and the Dynamics of Spin
By Steve Crandall
Vice President, Sales & Marketing
Ashaway Racket Strings
 Ashaway Racket Strings offers two versions of its popular PEEK-based tennis strings, 16 gauge (1.27 mm) MonoGut ZX, and 17 gauge (1.22 mm) MonoGut ZX Pro. MonoGut ZX Pro is a thinner lighter string, designed to provide even better elongation, snap-back and playability for players who do not require the added durability of a 16 gauge string. Both strings are available in black or natural with 100% PEEK monofilament construction, which provides exceptional dynamic stiffness and gut-like playability. |
As in politics, spin is all the rage in tennis these days. Everybody wants to improve their "up and down" game, and drop "heavy balls" like stones just inside the baseline. And to generate that spin many players also emulate the pros by using the "high tech" high-performance polyester strings. But what many find, unfortunately, is that polyester strings don't work as well for them. They feel like they have to work much harder with these strings to get less, and get worked over pretty hard by them in return. One fellow we know likened playing with polyester to "hitting a brick wall with a baseball bat."
So is polyester all it's cracked up to be when it comes to spin, and should you recommend it to your clients? The answer is yes, and no.
We talked about how stiff polyester strings are and how-in addition to rattling your teeth when you hit the ball-they actually generate less power than other string materials like gut and PEEK. So then, how is it possible for a string that generates less power to also generate more spin?
Crawford Lindsey and company at Tennis Warehouse University have studied spin extensively, and published a number of highly technical reports on the mechanics and physics of spin on the TWU website. Their comparative study, Which Strings Generate the Most Spin, concluded that polyester strings do indeed generate more spin: on average, about 20% more than nylon and 7% more than natural gut. But they also point out that:
1. The player has by far the larger role in generating spin. Racquet head speed, angle of racquet, and angle of swing basically trump all other considerations. Other non-equipment factors include incoming ball speed, angle and amount of topspin.
2. While string material, tension and stringing pattern do play a role, the key factor in this regard is lateral string movement and snap-back. Polyester strings simply move laterally more easily than nylon or gut, and thus produce more spin.
So what is it about polyester that allows it to move laterally? TWU suggests stiffness, tension loss, and slipperiness as the main candidates. "Polyester is stiffer, loses more tension, and is slippery. The stiffer material may be more able to overcome inter-string friction or move faster; the lower tension decreases inter-string friction enabling more movement; and slipperiness (low coefficient of friction-COF) also lessens inter-string friction. These may all act in interactive combinations to facilitate string movement and snap-back."
The key element here is inter-string friction. "Because polyester string is stiffer than other strings, it deforms the ball more, which loses energy, and this results in less power for the same swing. Because the ball had less speed, players swung faster to get more depth. But swinging faster (at an angle to the ball) causes more spin, so they could swing faster again, and so on - more speed, more spin, more speed, more spin."
In short, high performance polyester strings work for the top pros because they are top pros. They swing harder and faster, hit at better swing and racquet angles, and are more likely to hit with the sweet spot on the racquet. Thus, they are able to do things with these strings that the rest of us can't. But even the pros have their limits with polyesters. Many are stringing at lower tensions or going to hybrid set-ups to reduce stiffness and impact shock. And you'll notice that when they do occasionally off-hit, the ball goes zooming away like a rocket. High performance polyesters are like formula-one racecars: they take a lot of skill to drive.
So, what's a poor recreational player to do-or even a pro who's sick of getting beaten up by his string? Is there another way to generate spin?
Although Crawford Lindsey and company have yet to study it scientifically, reports we're getting at Ashaway from players of all stripes indicate that PEEK-based strings like our MonoGut® ZX and ZX Pro do indeed generate spin like polyesters, and do so more easily and more comfortably with less impact shock on players' arms and shoulders. To understand how this works, go back to our discussion of Dynamic Stiffness. Dynamic stiffness is a measure of a string's elasticity and ability to "snap back." The more a string stretches, the more power it returns to the ball. The less it stretches, the more energy is lost in flattening the ball and the less total power is available for rebound.
This is true regardless of whether a string stretches perpendicular to the string bed as in a straight hit, or lateral to the string bed in generating spin, so long as friction does not get in the way. The reason both natural gut and nylon generate less spin than polyester is because these strings are stickier than polyester. Their snap-back gets stuck. Gut is less sticky than nylon, but is still stickier than polyester. Our evidence suggests that PEEK is as slippery as polyester, especially when configured as a monofilament in MonoGut ZX. So you get more spin with less work.
This gives you the best of both worlds. Rather than a highly specialized 'formula-one' string, PEEK strings are like Porsches. You get all the power and handling of a finely built racing machine, but one that drives easily and can be taken on the road. But don't take our word for it. Before you recommend them, take one for a spin in your own racquet and see how it works for you.?
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