I gathered some information on the process of measuring string-tension

of the strings on tennis rackets. I post here a tutorial on how to

measure the string-tension on your racket.

First some introductory information :

1. one can measure the real physical tension (in kg) of a string

via measuring the base-frequency of the vibrating strings.

(i.e. if you hit the string-plane on your racket you can hear

a sound of certain frequency composition=pitch which depends

on the tension of the strings).

Let us call this the Frequency-method of measuring string-tension.

So one only needs to measure the base-frequency f0, plug it into

a formula and get the string-tension.

Here's the formula :

A : racket-head area

f0 : base-frequency of vibrating strings

mu : mass-density of strings

2. you string your racket with say 27 kg of pull tension, but due

to friction,stress-relaxation of the strings and other factors

the real tension after the stringing process is about ~35%

lower than your pull tension, i.e. only 17.5 kg. I mention this

because the frequency-method will measure this (lower) physical

tension on your strings, it will not the yield kg-values that you

used to string your racket with, because of the tension loss. So

don't be surprised when you later use the frequency-method an get

such low tension-values. Of course you can convert the measured

real-tension values in pull-tension values you're used to, by

"adding" the lost 35% of tension to the measured tension-value and

get a pull-tension value (that'll be a rough approximation).

Personally, I do this by stringing my racket at lets say x kg

and measure real-tension directly after stringing, lets say I

measure y kg afterwards. So the loss of tension was (x-y) kg = z.

This z-value is specific to the string I used and to my personal

stringing manner. Later when I measure the tension on my strings

I'll get the lower real tension, and to get the corresponding

pull-tension values I just add the z-value. This adjustment is

done because you're more used to the kg-values in the pull-tension

range [20,30] kg. Because you put 27 kg on your racket-strings

and when you play with your racket you play only with real 17.5 kg

on the strings, but you associate the feeling of these 17.5-kg-strings

to be 27-kg-strings, as that was the pull-tension you put on the

strings during stringing.

If you just want to measure differential tension loss you can

of course skip this conversion. In this case your not interested

in absolute kg-values, but you measure directly after stringing

a real string-tension of 18 kg and after 2 weeks you measure

only 16 kg, so you know you lost 2 kg of tension.

Now here's the tutorial as a PDF-file. I hope the reader can understand

the process of the frequency-method.

http://www.tennis-altensteig.de/marc/freqmess-eng.pdf

Have fun and I hope to see some feedback =)

Greetings Marc

Reference:

- Cross, R., & Bower, R. (2001). Measurements of String Tension in a Tennis

Racket. Sports. Eng, 4, 65-175