How much tension do tennis strings lose, and when should you restring?
Updated · Fernhart Labs
Short answer
Most of the loss happens during stringing and the first minutes after it, not over the following weeks. Measurements by physicists Rod Cross and Robert Bower found the tension in a racket immediately after stringing is typically about 30 % below the pull tension set on the machine with a nylon string, and about 40 % below with polyester. After that it keeps falling slowly, faster for polyester than for nylon.
The usual rule of thumb is to restring as many times a year as you play each week: twice a week, twice a year.
Where the tension goes
The machine pulls each string to the tension you set, but what stays in the racket is lower. Cross and Bower traced the drop to several effects acting together:
- Stress relaxation. A string held at a fixed length loses tension by itself. In their test, a fresh nylon string tensioned to 28 kg (about 62 lb) and clamped fell to about 24 kg (about 53 lb) within 15 minutes, then only another 1–2 kg over the next 24 hours.
- Frame distortion. The frame flexes slightly as the strings go in, letting some tension out.
- Friction. Strings are pulled at an angle through the grommets, and friction there leaves the tension in the racket 1 or 2 kg (about 7 %) below the pull tension. Friction where mains and crosses touch also plays a part.
Two more findings matter in practice: polyester strings lose tension more rapidly than nylon, and a string that has already been stretched loses tension more slowly than a fresh one.
What that means in pounds
Applying those percentages to a racket strung at 55 lb, as an illustration: right after stringing, about 38–39 lb remains in the string bed with nylon (30 % lower), and about 33 lb with polyester (40 % lower). That is why a tension meter, or a calibrated app, reads well below the number on your stringing ticket, even on new strings.
Meters therefore report on the stringer's scale: they compare readings with what the same racket gave when freshly strung, rather than claiming the absolute force in the strings.
When to restring: a schedule by how often you play
The rule of thumb used across the racquet industry is to restring as many times a year as you play per week. It is a convention, not a measurement; players on polyester, or who want a consistent feel, often restring sooner, since polyester loses tension faster.
| You play | Restrings a year | About every |
|---|---|---|
| Once a week | 1 | 12 months |
| Twice a week | 2 | 6 months |
| 3 times a week | 3 | 4 months |
| 4 times a week | 4 | 3 months |
| 5 times a week | 5 | 10 weeks |
For comparison, Cross and Bower note that a recreational player typically restrings every year or so, while professionals restring before every match so the tension is the same in every racket.
How to track tension loss at home
A strung racket rings like a drum skin when you tap it. Cross and Bower showed that the frequency depends mainly on the area of the string bed, not its shape, along with the tension and the strings' weight. Because frequency rises with the square root of tension, a 10 % drop in tension lowers the pitch by about 5 %.
That makes loss easy to follow without knowing the absolute tension: record the pitch right after stringing, then compare later readings with it. The ratio of the two pitches, squared, is the share of tension kept. An absolute figure needs a model of the frame, the pattern and the string, which is why any meter's uncalibrated reading is an estimate.
Questions
How much tension do strings lose in the first day?
Most of it is gone before you leave the stringer: about 30 % below the pull tension with nylon and 40 % with polyester, measured right after stringing. In the same study, a nylon string lost only another 1–2 kg over the following 24 hours.
Do strings lose tension if the racket isn't used?
Yes. Stress relaxation continues even when the racket sits in the bag, so strings lose tension with time as well as with play.
Does polyester lose tension faster than nylon?
Yes. Cross and Bower found polyester strings lose tension more rapidly than nylon, and lose more during stringing (about 40 % below pull tension versus 30 % for nylon).
How often should I restring if I play twice a week?
By the usual rule of thumb, twice a year, about every 6 months. Many polyester players restring sooner.
Why does my tension meter read lower than the tension I strung at?
Because the tension in the racket really is lower: typically 30–40 % below the machine's pull tension right after stringing. Compare readings with the same racket's reading when freshly strung.
Can a phone app measure string tension?
A phone can measure the pitch of the string bed accurately, and the change in pitch gives the tension lost exactly. Turning pitch into an absolute tension needs assumptions about the frame and strings, so it is best calibrated against a freshly strung reading.
Stringbed: Tension Meter
String tension meter for tennis, squash and badminton rackets.
Stringbed measures the pitch of your string bed from a tap and shows how much tension each racket has kept since its first reading, on a chart per racket. Calibrate it within a few hours of stringing and every later reading is on your own stringing scale. It keeps a log of every string job and reminds you when to restring by the rule above or by the loss you choose.
Coming soon to Google Play In review at Google Play; the link appears here when it is live.
Sources
- R. Cross and R. Bower, "Measurements of string tension in a tennis racket", Sports Engineering 4 (2001) 165–175 PDF (University of Sydney)
- The "times a week = restrings a year" rule: the racquet industry's usual advice (a convention, not a measurement)