When stringing, for example in a shop or at big tournaments like Rotterdam, Rosmalen, or even the Grand Slams, stringers often get questions about the tension (in kilograms) of tennis rackets. One common question is: “What is the average tension that players have on their racket?”
Pro Tour stringer Timo van Driel explains why this cannot be answered in one sentence:
Sheet size:
There are differences in the size of the racket head. Roger Federer played for years with a relatively small Wilson racket, while Rafael Nadal plays with a larger head. To get Nadal's racket as tight as Federer's, it has to be strung about three kilos harder.
Stringing pattern:
Rafael and Roger use a stringing pattern of 16 length strings and 19 cross strings, while Novak Djokovic uses an 18 by 20 pattern. Although Rafa and Novak have the same head size, Djokovic's pattern makes his racquet feel tighter at the same tension, because more strings are pulled.
Type of strings:
The type of string also matters. On Tour, the most popular choices are gut strings and polyester. Gut strings have different elasticities and respond differently to pre-stretching. Polyester strings generally require less tension than nylon or multifilament strings, and different polyester strings can also vary in hardness.
The exact average string strength of players is difficult to determine because of all the variables such as blade size, string pattern and string type. What can be measured is the hardness directly after stringing. This gives a better picture of the player's game type and how the racket variables behave. So don't let the string strength be leading, but always ask for good advice!