Rackets and racket string have to work together as a unit

CHANGES IN STRING TENSION
AFFECT RACKET PERFORMANCE

Rackets and racket string have to work together as a unit, and choosing the right string tension is one of the most important equipment decisions a badminton player can make. It used to be a no-brainer back in the "old days," when all rackets were made from the same material (wood), all had the same head shape, and were all strung at 15 lb. of tension. But technology hasn't stood still, and stringing choices have become more complex.

There are now many different racket head shapes, sizes, and stringing patterns, and wide variation in shaft action, from flexible to super-stiff. String tension must be selected with all of these factors in mind. Recommended stringing tensions now range from 15 to 24 lb. This means there's a lot of room for error. Or to look at it in a more positive light: there's greater opportunity for the player to "tune" his racket to suit his playing style, by altering string tension over a wider range. If you don't like your racket's performance, don't even think about buying a new one until you've experimented with changes in string selection and tension.

The basic equations are these:

Higher Tension =	More Control
Lower Tension =	More Power

Strings at low tension stretch more when they contact the shuttlecock, and then quickly snap back to their initial length. This "trampoline effect" (also known as resilience, or rebound) adds power to the shot: it's sort of like putting a spitball in a rubber band, pulling back, and then releasing it. If the racket is strung at a higher tension, there's less stretch left in the string to provide trampoline effect. On the other hand, tighter strings remain flatter, so it's easier to control the direction of the shuttlecock. Bear in mind these limits, however: excessive string tension leads to frame or string breakage, and too-low tension means a total loss of both control and power.

A racket loses roughly 10 percent of its tension the day after it's strung-and that's if it's not used. The tension will drop further every time you play it. "Creep," or loss of tension, is due to stretch at the molecular level, and it's a fact of life: work with it, don't fight it. Think of stringing tension in terms of initial, or "reference" tension. Learn what reference tension works best for you over the useful life of the string, and go with that.

Checking tension on an already-strung racket can be done with special equipment, but it's not a very fruitful exercise. When the string becomes too loose (if you haven't already broken it),
that means the molecules have stretched out considerably, and tightening up the string in the racket won't restore its original resiliency. So don't even bother trying to measure the tension of a strung racket: just re-string it.

The construction of the string itself also affects string tension and performance. String cores, which provide the primary strength and power characteristics, are made from a number of different polymers, each with different levels of elasticity, tension-holding ability, durability, etc. The filaments that make up the core vary in size, number, and orientation (i.e., straight or twisted) between different models of string. Similar issues apply to the jacket, which provides the string's main abrasion resistance and "control" characteristics. The point I'd like to emphasize here is that string construction is a very technical subject that is really understood only by specialized textile engineers. In general, players should ignore the technical details and pay attention instead to how a string feels and plays.

It is always a good idea to discuss your needs with a certified racket technician who specifically understands badminton. But understand that string tension is more like an exam in English than Math: there is no single right answer, and the final decision has to be the player's own, based upon his or her abilities, playing style, and preferences. If you're physically strong, you might want to add control to your game by stringing tight. Or you might want to make your shots even more powerful by stringing loose. Or you might choose something in between for a balance of control and power. Likewise with finesse players who are not so strong: you can select string tension to maximize your advantages, minimize your weaknesses, or strike a happy medium. By knowing how string tension affects play, you'll optimize your own performance and that of your racket.

Source : USA Badminton