String Tension, Temperature and Climate
Short answer: Cold strings play stiffer and hot strings play softer. In laboratory testing for Tennis Warehouse University, heating a string after it had been tensioned and had settled, as happens in a hot car, caused 30 to 76 percent more tension loss than at room temperature, and the loss did not come back when the string cooled. The testers’ advice is to string lower for cold and higher for hot on-court temperatures when you string just before a match. No source publishes how many pounds per degree, so treat any seasonal change as a test of one small step, and compare readings only when they are taken under similar conditions.
How heat and cold change tennis strings
Crawford Lindsey of Tennis Warehouse and Rod Cross of the University of Sydney tested 14 strings (one natural gut, one Kevlar, seven nylon and five polyester) at 0, 20 and 40 °C (32, 68 and 104 °F). They stretched single strings in a test rig, not strung racquets, so the results describe the direction and rough size of each effect rather than a number for your stringbed.
| Condition | What changed | Size in the test | Evidence class |
|---|---|---|---|
| Warmer string | Lower stiffness: the string plays softer | Every string was less stiff at 40 °C than at 20 °C, by 1.2 to 14.6 percent depending on the string | Retailer laboratory test with a university physicist |
| Colder string | Higher stiffness: the string plays firmer | Most strings in the 0 °C table were 2.0 to 10.9 percent less stiff at 20 °C than at 0 °C; one nylon string went the other way | Retailer laboratory test with a university physicist |
| Heat after tensioning | Extra tension loss that stays after cooling | 30 to 76 percent more tension loss than at room temperature | Retailer laboratory test with a university physicist |
| Material | Nylon stiffness reacted more to temperature than polyester | Natural gut changed 2.0 percent from 20 to 40 °C | Same test; one gut string only |
The authors stress that stiffness, not tension alone, is what most influences performance and feel, and that tension is one component of stiffness. They also note that the ball changes with temperature and the player may feel stiffer on a cold day, so what you feel on court is the combined effect. The guide to tennis string types explains how each material is built.
Does leaving a racquet in a hot car lose tension?
Yes, according to the laboratory result, and it is the largest effect the test found. Lindsey and Cross write that exposing a string to high temperatures after it has settled, “as in leaving the racquet in the car during hot weather,” produces the greatest decrease in tension, and that heat after stringing matters more than heat during stringing. When the heat is removed, the string settles again at a much lower tension. Chilling the string reverses very little, and the authors say the difference is probably not perceptible and does not last.
Tennis Warehouse’s summer checklist, which is retailer guidance, gives the practical version: on hot days, keep your racquets out of the car for long periods. A cold car is a different case: the strings play stiffer while they are cold, but the test did not measure a strung racquet left in the cold, so there is no laboratory figure for it.
If a racquet has spent an afternoon in a hot car, treat the stringbed as changed. Take a fresh reading and compare it with your baseline before you decide anything, because the tension-loss estimates assume ordinary storage.
Why temperature changes your readings
Temperature changes stringbed stiffness while the racquet is warm or cold, and heat after stringing lowers tension itself. A reading taken straight after a session in the sun and one taken in a cool room the next morning therefore mix two kinds of change: the real loss since your baseline, and the temperature on the day.
This is String Tension AI’s interpretation of the laboratory result: the useful comparison is between readings taken under similar conditions, ideally at room temperature, with the same method. A difference that appears only when the temperature is different is not yet evidence that the strings are going dead. The checklist below sets out the routine.
Indoor and outdoor tennis
Indoor courts are usually kept within a narrower temperature range than outdoor courts across the year, so an indoor player has less seasonal reason to move tension. That is a club heuristic, not a measured result: no source here compares indoor and outdoor stringbeds directly.
Outdoor players face the change the laboratory describes. In summer the stringbed plays softer and the ball tends to fly further; Tennis Warehouse’s summer checklist notes that more balls fly long in hotter weather. In winter the stringbed plays firmer. If you split the year between indoor and outdoor courts, record which one each reading and session came from, as the app’s indoor and outdoor environment field and the stringbed log notes allow.
Does altitude change string tension?
The rules handle altitude through the ball, and no source here shows that altitude changes the strings themselves. The ITF provides a pressurised ball designed for high altitude, and says pressureless balls are also suitable at altitude provided they have been acclimatised there for 60 days.
Some players do adjust. Babolat quotes Rafael Nadal: “I always played with the same tension, 25 kg under normal conditions. At altitude, I opted for 25.5 kg.” That is 55.1 lbs normally and about 56.2 lbs at altitude, a change of roughly 1 lb. It is one professional’s choice with his own string and frame, not a formula for anyone else; the pro string setups table explains why professional settings are context rather than targets.
Pressurised and pressureless balls
The ITF explains that a pressurised ball is inflated, typically 10 to 13 psi (70 to 90 kPa) above atmospheric pressure, while the air inside a pressureless ball is at atmospheric pressure. A pressurised ball gets more of its bounce from that internal pressure; a pressureless ball gets more from its thicker rubber core.
No source here gives a tension adjustment for ball type. The practical rule is about testing: if you switch between pressurised and pressureless balls, or between new and worn balls, do not change tension in the same week, or you will not know which change you felt.
Humidity and natural gut
Natural gut is the string most associated with humidity. The ITF describes natural gut’s durability “in terms of wear and moisture resistance” as mediocre, and the manufacturing process ends with a protective polyurethane coating. Tennis Warehouse’s retailer guidance adds that the coating on modern gut strings helps protect them from changes in the weather, particularly by increasing resistance to humidity.
None of the sources here gives a tension adjustment for humidity. In a humid climate, keep gut dry, avoid playing it in the rain where you can, and rely on your own readings: if the stringbed changes faster in the humid months, your log will show it. The polyester and natural gut comparison covers how gut holds tension in normal conditions.
Should you change string tension for the season?
The laboratory direction is clear: lower for cold, higher for hot. The amount is not published, so the band below is String Tension AI’s club heuristic. It moves by at most one 2 lb (0.9 kg) step from the reference tension you use in mild conditions, the same step the tension calculator uses for fine-tuning. It is a band to test for one string job, not a rule.
Natural gut in a humid climate: the ITF rates gut’s moisture resistance as mediocre. Keep it dry and watch your readings rather than changing tension for humidity.
This is a band to test, not a rule. Change one thing per string job, take a fresh baseline reading after stringing, and keep the change only if comfort and control are better.
| Climate | Winter | Spring | Summer | Autumn |
|---|---|---|---|---|
| Cool | Up to 2 lbs lower | Up to 2 lbs lower | Hold | Up to 2 lbs lower |
| Temperate | Up to 2 lbs lower | Hold | Up to 2 lbs higher | Hold |
| Hot and dry | Hold | Up to 2 lbs higher | Up to 2 lbs higher | Up to 2 lbs higher |
| Hot and humid | Hold | Up to 2 lbs higher | Up to 2 lbs higher | Up to 2 lbs higher |
Indoor play holds the reference in every season. Two lbs is about 0.9 kg. The direction comes from the Lindsey and Cross test; the season and climate grouping and the size of the step are our heuristic. A band that includes your reference means “no change” is always a valid result: if the stringbed already plays well, keep it. Stay inside the range printed on your racquet whatever the season.
Measure under similar conditions
These steps are String Tension AI’s routine for keeping temperature out of your comparisons.
- Measure at room temperature. If the racquet has been in a cold car or in the sun, let it settle indoors before you take a reading.
- Use the same method and the same spot on the stringbed each time, and keep a dampener on or off consistently. The guide to measuring string tension compares the methods.
- Take three repeat measurements and check their spread with the repeatability checker before trusting a single number.
- Note indoor or outdoor play and the conditions with every reading, so a seasonal pattern is visible later.
- Compare with your own baseline, not with the stringing-machine setting, using the racquet tension checker.
- Treat known heat exposure as a real change. After a hot car, take a new reading; the laboratory loss from heat does not reverse when the strings cool.
String tension, temperature and climate: FAQ
Does cold weather make tennis strings tighter?
Cold makes strings play stiffer. In laboratory testing for Tennis Warehouse University, most strings were stiffer at 0 °C than at 20 °C, and every string was less stiff at 40 °C than at 20 °C. That is a change in how the stringbed plays while it is cold, not a recovery of tension already lost.
Does leaving a racquet in a hot car lose tension?
Yes. The same laboratory test found that heating a string to 40 °C after it had been tensioned and had settled caused 30 to 76 percent more tension loss than at room temperature, and the loss stayed after the string cooled. Keep racquets out of hot cars and take a fresh reading if one has been left in the heat.
Should I string tighter in summer?
The testers advise stringing lower for cold and higher for hot on-court temperatures when you string just before a match, but no source publishes how much. String Tension AI’s seasonal helper suggests a band of up to one 2 lb (0.9 kg) step from your mild-weather reference tension, as a test for one string job rather than a rule.
Should I change string tension at altitude?
There is no general formula. The ITF provides balls designed for high altitude, and Babolat quotes Rafael Nadal raising his tension from 25 kg to 25.5 kg at altitude, about 1 lb. That is one professional’s choice; if you play at altitude, test one small change and compare readings with your own baseline.
What the sources support
Lindsey and Cross support the stiffness changes with temperature, the extra tension loss from heat after tensioning, the hot-car scenario and the direction of a seasonal adjustment, measured on single strings in a laboratory rig. The ITF strings document supports natural gut’s moisture resistance and coating; the ITF balls document supports the altitude ball rules and the pressurised and pressureless construction. Babolat supports Nadal’s altitude quotation, and only for his own setup. Tennis Warehouse’s summer checklist and natural gut guide are retailer guidance. The seasonal band, its climate grouping and the measurement checklist are String Tension AI’s method.
Accessed October 3, 2026
- Lindsey C, Cross R — The Effect of Temperature on Tennis String Tension and Stiffness, Tennis Warehouse University (June 6, 2016) for stiffness, tension loss and heat exposure at 0, 20 and 40 °C (retailer laboratory test with a university physicist).
- International Tennis Federation — Rackets and Strings: Strings (November 2019) for natural gut’s moisture resistance and coating (governing-body technical guidance).
- International Tennis Federation — Equipment: Balls (November 2019) for high-altitude balls and pressurised versus pressureless construction (governing-body technical guidance).
- Babolat — Rafael Nadal for his quoted normal and altitude tensions (manufacturer-published player quotation).
- Tennis Warehouse — Your Essential Summer Tennis Checklist for keeping racquets out of hot cars and balls flying long in heat (retailer guidance).
- Tennis Warehouse — Pros and cons of natural gut tennis string for the coating’s resistance to humidity (retailer guidance).
See whether the season is changing your stringbed
Take a fresh baseline after stringing, then compare readings taken under similar conditions through the year, so a seasonal pattern shows up in your own history instead of in a guess.
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