Newberry said:
Interesting how many of the 18g strings outperform their 16g counterparts for tension loss. Opposite of what I would have thought...
* About half of all thin strings are stiffer than thick versions of the same string. The reason is that the stress (tension per square inch) on the thin string is larger and that the stiffness of most strings increases quickly when the stress increases above a certain value. A thin string will generally stretch further than a thick string when it is strung at 60 pounds, but it often stretches less than a thick string when the tension rises above 60 pounds during a shot.
String stiffness is a combination of material, gauge (i.e., string diameter and, thus, amount of material), length, and tension. But it is not a single number that is the same all of the time such that you can say, "This string has a stiffness of such and such." The stiffness of the string changes depending on what the tension is before you start stretching it. A string at 50 pounds will stretch more for each pound of impact force compared to a string at 70 pounds. In other words, the string is stiffer at higher tensions, not just because of the tension, but also because of a change in the material property itself. This is a property of all common string materials. A steel string would not act that way. It would stretch lengthwise the same amount for each pound of impact force whether it were strung at 40, 60, or 80 pounds, and you could say that the steel string has a definite value for lengthwise stiffness. Fortunately, in the normal stringing range of 50-70 pounds, different string materials don't change stiffness radically compared to each other as tension is altered. So, if one string is stiffer than another at 50 pounds, it is, for all practical purposes, safe to say that it is stiffer by about the same proportion at 70 pounds. Each string will feel about the same relative to the other at each tension. However, they will each feel stiffer than they did at the lower tension. The one exception is gut, which is stiffer at lower tensions compared to nylon, but the stiffness stays relatively constant at the ranges of higher tensions caused by ball impact, and it is less stiff than other strings at these tensions as a result.
As the String Selector shows, there are only four different string materials in common use. In order from softest to stiffest they are: gut, nylon, polyester, and aramids, such as Kevlar. These groups have very little, if any, overlap in measured stiffness values from one group to another. There is beginning to be a tiny bit of overlap between nylon and polyester (but only for a very few strings), as new manufacturing processes have allowed polyester to be softened. Within each category, there is a range of variance, but nothing as significant as the leap between separate categories.
The Selector Map also plots tension loss. This is a property of the material and is related to stiffness because it determines the consistency over time of the stringbed stiffness. Every string loses tension from the second it is installed and with every hit of a tennis ball. The rate of tension loss determines how much and how quickly the stiffness of your stringbed will change and, with it, the performance and feel. The tension loss was measured by pulling the string to 62 pounds, waiting 200 seconds, and then impacting the string five times with a force comparable to hitting a 120 mph serve. The tension loss is thus a combination of static time tension loss and dynamic impact tension loss. Polyester loses the most tension and gut the least.
The rate of loss slows to a mere creep after a couple of days and remains "perceptually" about the same for a few weeks. This means different things to different players. If you are a typical recreational player, the feel you are looking for is the stabilized feel that you experience after a couple of days and then for weeks after. If you are a pro, you need your racquets to feel exactly the same every day. That is why high level players restring so frequently.
The Selector Map also plots tension loss. This is a property of the material and is related to stiffness because it determines the consistency over time of the stringbed stiffness. Every string loses tension from the second it is installed and with every hit of a tennis ball. The rate of tension loss determines how much and how quickly the stiffness of your stringbed will change and, with it, the performance and feel. The tension loss was measured by pulling the string to 62 pounds, waiting 200 seconds, and then impacting the string five times with a force comparable to hitting a 120 mph serve. The tension loss is thus a combination of static time tension loss and dynamic impact tension loss. Polyester loses the most tension and gut the least.
The Selector Map also plots tension loss. This is a property of the material and is related to stiffness because it determines the consistency over time of the stringbed stiffness. Every string loses tension from the second it is installed and with every hit of a tennis ball. The rate of tension loss determines how much and how quickly the stiffness of your stringbed will change and, with it, the performance and feel. The tension loss was measured by pulling the string to 62 pounds, waiting 200 seconds, and then impacting the string five times with a force comparable to hitting a 120 mph serve. The tension loss is thus a combination of static time tension loss and dynamic impact tension loss. Polyester loses the most tension and gut the least.
The rate of loss slows to a mere creep after a couple of days and remains "perceptually" about the same for a few weeks. This means different things to different players. If you are a typical recreational player, the feel you are looking for is the stabilized feel that you experience after a couple of days and then for weeks after. If you are a pro, you need your racquets to feel exactly the same every day. That is why high level players restring so frequently.
String stiffness and tension loss are just two variables in overall stringbed stiffness. Table 1 summarizes the effect of additional variables that affect that stiffness, and Table 2 summarizes the resulting affect on performance.
http://www.racquetsportsindustry.com/issues/200509/200509stringselector.html
