When reading about strings and their properties, you will come across several unique terms and plenty of stringing jargon. Some common terms are as follows:
Actual tension The tension in a strung racket. The actual tension is almost always lower than the reference tension, primarily due to string creep (relaxation). The amount of tension loss depends on the type of string and stringing machine used, racket head size and also stringer skill level / techniques.
Bite Thin strings present less surface area and penetrate the surface of the ball deeper on impact, giving players better control over ball placement. This concept is known as string bite.
Dwell time The length of time the ball stays on the strings upon impact is referred to as the dwell time.
Dynamic stiffness Dynamic stiffness is a measure of how much a string stretches when it is quickly impacted, i.e. when it strikes the ball. The less a string stretches, the stiffer it is. The more it stretches, the more energy it returns to the ball. Dynamic stiffness can be likened to elasticity and is measured in units of how many pounds of force it takes to stretch the string one inch. Natural gut has a low dynamic stiffness compared with nylon and other synthetic materials.
Gauge Gauge corresponds to the thickness of the string. The higher the gauge, the thinner the string.
The 'L' in 15L and 16L stands for 'light'. The gauge designations originally corresponded to American wire gauge (AWG) thicknesses, but were later relaxed to represent a range of allowable diameters, rather than a single, exact size.
Hybrid stringing Hybrid stringing combines the stiffness and durability of polyester or Kevlar strings with a softer string for playability. Hybrid setups usually consist of a polyester/Kevlar string in the mains and a synthetic string or natural gut string in the crosses.
Proportional stringing Proportional stringing is a method of stringing in which each string is pulled to a tension proportional to its length, such that the relative stiffness of each string is the same.
Reference tension The tension setting that a racket is strung at, otherwise known as the machine tension.
Relative tension At the same reference tension, a thinner string is stretched more than a thick one, so the thin string behaves as if it is tighter a phenomenon known as relative tension.
Soft If a string is soft, it absorbs the force of impact with the ball, not the racket or the player’s arm. Soft string materials have low dynamic stiffness.
String creep A gradual loss of tension over time, at the molecular level. A racket loses roughly 10% of its tension the day after it's strung, even if not used. The more you play, the greater the loss of tension.
Sweet spot The sweet spot is the area of the racket stringbed where impact with the ball results in the least vibration and force transmitted to the hand. It is located near the centre of the strings. A common misconception is that the sweet spot also produces the most power this is not strictly true, as the power point is located towards the throat of the racket, near the centre of mass.
Tension Tension is measured in pounds (lb or lbs). Tension is sometimes (but less commonly) referred to in kilograms (kg).
Trampoline effect At low tension, strings stretch more when they contact the ball and quickly rebound back to their initial length, imparting more power to the ball. This trampoline effect is less pronounced if the racket is strung at a higher tension, as there is less stretch left in the string.