The science of strings: understanding and choosing from N°1 to N°7
Updated: 2 hours ago
The string is the only part of your racquet that touches the ball, and the only one you replace several times a year. It is also the only part of the racquet you replace several times a year — and the one most often chosen out of habit or on someone's recommendation.
There is nothing here to believe. Three measured quantities are enough to place any string and to predict what it will do in your racquet.
1. Elasticity: what the string gives back
Under tension a string stretches. How much it stretches, and how that changes as tension rises, describes almost everything. A string that stretches a lot stores and returns more: more power, more comfort, a longer dwell time — the time the ball stays on the strings. A string that stretches little holds its geometry: more control, more predictability, drier feedback.
This is not a matter of good or bad. It is the axis that orders the range, from N°1 — the softest and most powerful — to N°7, the stiffest and most control-oriented.
2. Linear density: the mass you put in the bed
At equal diameter, two strings do not weigh the same. That mass per metre changes the inertia of the string bed, and therefore how it absorbs and returns. It also explains a point players forget: changing string changes the racquet's swingweight. You are not only changing a feel, you are changing a setting.
3. Structure: what the string does to the ball
Round, octagonal, pentagonal, hexagonal, textured: geometry decides how the string bites the ball and how well it returns to place after the strike — snapback. Two rules, without exception:
A round string does not bite. It slides, it snaps back well, it lasts. Do not ask it to create spin in your place.
A hexagonal string does not slide. It bites, it adds spin to a stroke that already produces some, and it wears faster. Do not ask it for the life of a round string.
What the N°1 to N°7 range really orders
One visible axis, three quantities behind it. N°4 is the balance point of the range, and its shape is what explains it: it is octagonal, where N°5 is round. Its edges are what make the difference: for the same swing, N°4 bites the ball more, and it is that bite which makes it generous for the greatest number. N°5, smoother, is the choice of feel, control and predictability — and it lasts longer. N°4.5, pentagonal, sits between the two: in 1.25, its curve runs between the N°4 and the N°5 over almost the whole range. Numbering rather than naming is not a stylistic tic: a name tells a story, a number places you.
Tension drops, and that can be measured
A string loses tension from the moment it is installed, then keeps losing it. The range is recorded gauge by gauge: eight strings, each characterised by its elongation curves, with one gauge still to come — the N°4.5 in 1.20, which the module shows as not recorded rather than interpolating a plausible figure. They are plotted in the graph on the Understand page. That is the kind of data that should ship with every string sold.
The range, in order
One axis, eight references, and the gauges actually available on each. It is the only table you need in order to place yourself.
N°1 — multifilament, the softest and most generous in return. One of the two to look at first for a sensitive arm. Gauge: 1.30.
N°2 — the other choice for a sensitive arm, one step firmer than N°1. Gauge: 1.30.
N°3 — the entry to the control half of the range. Gauges: 1.20 · 1.25 · 1.30.
N°4 — octagonal. The balance point of the range and the most versatile of the seven: its softened edges bite more than a round without wearing like a hexagonal. Gauges: 1.15 · 1.20 · 1.25.
N°4.5 — pentagonal, between N°4 and N°5. Sharper edges, more definite bite, slightly shorter life. Gauges: 1.20 · 1.25 · 1.30.
N°5 — round. The choice for feel, control and predictability, and the one that lasts longest. Gauges: 1.25 · 1.30.
N°6 — the number for chronic string breakers. Gauges: 1.20 · 1.25 · 1.30.
N°7 — stiff hexagonal, the most controlling in the range. Gauges: 1.20 · 1.25 · 1.30.
Two things follow. First: not every reference offers every gauge, so changing gauge sometimes means changing number — and that is a different decision. Second: N°1 and N°2 exist only in 1.30, which is consistent with what is asked of them, softness rather than life.
The protocol, in one sentence
The curves that order this range are taken on a 180-millimetre gauge length, in rising tension steps, same bench and same sequence for all eight references. That constancy, and nothing else, is what allows anyone to say one number is softer than another.
The detail of the reading, what follows from it and what does not, is in the article on the curves.
What those three quantities do not say
They do not say durability. Abrasion is a fourth phenomenon, readable in none of the three, and measured in playing sessions rather than on a bench.
Nor do they say what happens during the few milliseconds of contact. The bench works in slow traction; what tension becomes at impact follows from it, and that is where the difference between two neighbouring numbers is decided.
Choosing yours
Three questions are enough: what you want to feel at impact, how much spin your stroke already produces, and how often you break. The configurator asks them, and the string map places the answer in the range.
The bench gives elongation under a slow pull. A strike lasts a few milliseconds: what tension becomes at impact follows directly from these curves, and it explains why two neighbouring numbers do not behave alike in play.
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