String Tension

Generally there is a recommended “string tension range” for any racquet that is likely to be suitable to most poeple's requirements and the chances are you’ll be happy with a tension in the middle of this range. You may know you like a slightly tighter or lighter tension and advise accordingly and be done with it even if you don’t know why. If you are however interested in how these factors interplay and fancy tuning your string and tension to your game then read on....

General guidance on tension

Lower tension gives more power:  There is more elasticity available in a string with lower tension providing a larger “trampoline effect” and thus more additional power. Thinking used to end at this point: Research has shown that there is another factor to consider. The point at which the extra power is added to the shot (the injection of the recoil or the “trampoline effect” of the strings) tends to be when the racquet is past the low point of the shot and on the rise so it actually adds to the depth of the shot. Thus the more current thinking has it that lower tension adds depth to shots.
Lower tension leads to string wear:  There can be a durability issue for lower tension string-beds caused string on string abrasion. The lower tension allows greater string movement than would be the case at higher tension resulting in strings wearing each other out - particularly for hard hitters.
Lower tension gives a different feel:  Some players like the feel of lower tension as the ball dwells on the strings for longer and the strings fold more around the ball. As the ball longer this gives more opportunity for variation of racquet face angle or direction during the “point of impact” detracting from or adding to control. ie: more cut can be deliberately applied with a looser string or more inadvertent direction can be added with an out of control swing!
Lower tension reduces control:  If a ball is hit off centre on a loose string-bed then the trampoline effect will not be symmetric. The strings on the shorter side will recoil quicker than the strings on the long side giving an uneven “trampoline effect” imparting an unintended directional bias to the ball thus detracting from the control.
Higher tension improves control: Tighter strings stretch less thus retaining a flatter string-bed through the shot which enables the player to better control the direction of the shot. For players who hit the ball hard the force of the faster swing can generate sufficient elasticity on a tight string-bed for plenty of power and with less loss of control than would occur at lower string tension. Hard hitters can thus use higher tension to compenate for loss of control.
Higher tension increases chances of string breakages:  The durability issue for higher tension string-beds is overstretch failure caused by the impact of the ball on an already tight string-bed, particularly for hard hitters. The strings are simply more prone to snap because of the load imposed on them. Tightly strung strings often break where they pull hard against the grommets (the plastic protectors) in the racquet frame holes, or even sometime the string end knot.

So what does all that mean?If you don’t know what tension you like then stick with a mid tension. If you can generally place the ball where you want to but would appreciate more power then try a lighter tension (or one of the power frames at the same tension - If you’re also a big hitter then avoid one of the power frames as this is likely to cause you loss of control and string on string wear).If you have plenty of power but would like to improve your ability to place the ball where you want then ask for a higher tension.

String tension over time
String tension is reckoned to drop by 10% within a day of the racquet being strung. This is due to creep in the string material, the molecules of which resettle in a different position to each other and stop trying to return to their original positions. For this reason don’t judge the string tension if you use it within the first day of it being strung as it will have changed, permanently, by the next day. Tension continues to drop over time and more so the more the racquet is used. It can’t be avoided though different materials will suffer this to different degrees: It is one area where the cheaper monofilament strings win over the usually superior multi-filaments, the mono-filament being better at holding the string tension over time.
A string-bed that loses tension to creep as described above obviously has less tension as a result but it does not provide the additional power associated with lower tension as the string has also lost its elasticity and thus has a reduced trampoline effect.
If a string tension is important to you and you use a multifilament string you may want to restring more frequently in order to achieve tension consistency. Alternatively you might prefer to move to a narrower gauge string which can give improved playing characteristics but wear out naturally (through string on string wear or natural string breakage) more quickly before any noticeable loss of performance through creep in the string material. This way natural string breakage on a higher performance string prevents an insidious slide into playing with dead strings.

Materials and construction
Generally different string materials are chosen for different playing characteristics rather than the tension at which they’re strung. Polyester can be good for big hitters who consistently break their mains with other string materials. It doesn’t however demand a different tension. The multi filaments (microfilaments) are generally accepted as better at emulating the playing characteristics of gut better than other strings but again they don’t demand a different tension.
Probably the most relevant tension consideration for the average player regarding materials and construction is the fact that the monofilaments tend to retain their tension better over time than the multifilament’s. To find out why read on.
Infrequent player
Well if you’re a “once a fortnight” or even a “once a month” kind of player then you’re unlikely to wear your strings out. For you the relevant issue is that the material from which your strings are made will creep over time and they’re likely to feel dead after a few months unless you have the racquet restrung when the strings actually look fine. As the onset of creep in the strings is so infinitesimally slow you’re unlikely to notice until one day you just realise the racquet feels dead – probably after you’ve tried using your mate’s racquet for a few shots and suddenly realised what strings with life in them feel like again. Rather than choosing a string for its playing characteristics you’re probably better choosing a string for its tension holding characteristics so you should choose a monofilament rather than a multifilament .
More frequent player
If you play weekly or more frequently you’re more likely to wear your strings out (ie: they physically break) rather than have them go dead through creep of the string material. As you play more frequently you’re also likely to be more interested in a premium string acknowledged as having better playing characteristics. For you the optimum string is probably a multifilament. The downside is the strings will loose more tension and feel deader if you leave it for months in the cupboard than would be the case with a monofilament but as you play regularly this is not an issue.

Head shape and stringing pattern
What relationship does the racquet head shape and the stringing pattern have to the optimal tension for a racquet?
Some racquets have small compact heads and some have larger longer, wider (or both) heads. In the squash world for instance some Prince and Head racquets have elongated heads with longer main strings. Other factors remaining equal such heads can add power to the game of the average player. Strictly speaking it’s not the tension in the string that matters but the tension per unit length – the same tension across a longer racquet head gives lower “tension per unit length” which is equivalent to lower tension which is why it increases power.
If you choose such a racquet (power frame) then ask for it to be stung up at higher tension then you’ll loose some of the benefit of the extra power it can add to your game. There may however be other valid reasons to want it at a higher tension (to reduce string on string wear) but this is unlikely. The same consideration applies to the oversize racquets popular in the tennis world for beginner/intermediate players.
A similar tension consideration applies to the stringing pattern as to the length of the strings. A typical squash racquet for instance has 14 main strings, sometimes 12 or 16 but usually 14. Generally there will be more crosses than mains and also generally if there are more than the avergae number of mains in a racquet there will be more than the average number of crosses too - the racquet will have a denser stringing pattern. Typically main strings in a squash racquet will be strung at around 28 lbs on each. Compare the typical sum of the tensions across the mains of a 12 string racquet versus a 16 string racquet: 336 lbs versus 448lbs: 112lbs is 8 stone - across the mains only - This is a considerable difference in tension! Both racquets strung at the same tensions will feel very different and the 12 string racquet is going to feel like it gives more power as there will be more stretch in the string-bed for any given shot. So again if you’ve chosen a racquet with a sparse (as opposed to a dense) stringing pattern and then ask for it to be strung up at a high tension you’ll loose some of the benefit of the extra power it can add to your game. Again there may however be other valid reasons to want it at a higher tension (to reduce string on string wear) but this is unlikely.

Tension and sweet spot
The sweet spot is the point in the string-bed where the injection of extra power from the resilience of the string returning to its original length after being stretched, known as the trampoline effect, is at its maximum. It will be at the centre of tension of the string-bed and will dissipate in effectiveness the further from this point. The increase in the trampoline effect at this point on the racquet adds considerably to the power of the shot. The size of the effective sweet spot can be increased by using a larger racquet head, using a thinner gauge string or using a lower tension.