Let’s Talk About This!

I decided to write about this again after reading some posts asking questions, good ones by the way, about string tensions when stringing a racquet.

What we are discussing is not a simple matter, in fact, it is challenging to quantify many things we believe are real.  It is difficult, if not impossible, to tell a stringer how to string a racquet for a new client.  These are the obvious player/stringer questions that need to be answered:
a. What racquet type?
b. What string type?
c. What main and cross string tensions should be pulled?
d. What stringbed (SBS) stiffness is wanted?
e. What racquet weight, swing weight, and CG is wanted?
f. What stringing machine should be used (yes this matters, but is rarely considered!)?

There are also many player-specific questions that are in the mix, including:
a. Do you want more or less power?
b. Do you want more or less control for that power?
c. Do you want to hit with more spin?
d. Do you have any physical problems influencing your play (sore shoulder/arm, elbow, strength, etc.)?

The task/responsibility for a good stringer, or, racquet technician preferably, to his player is quite daunting if the goal is to “string responsibly.”

With answers to these questions, and a stringers plan in place to achieve these goals, one of the most important attributes a stringer can deliver is repeatability. Once a player has settled on a path (racquet, strings, tensions, stringbed stiffness (SBS), etc. you want, as a client and stringer, that customized performance to repeat with every re-stringing. So the stringer must have a process, with metrics, that will guarantee that repeatability. This repeatability is also the foundation for changes from that norm (for example, what happens if I replace my strings with another type, or if I stay with the same strings but switch racquets, etc.)

My comments that follow is the plan I have developed for my stringing process for the players I try to support.

One of the most important influences on how a racquet plays is the stringing machine that is used to string a racquet.

About twenty years ago I developed a machine evaluation procedure for understanding what happens during, and after, the stringing process.

Every machine is treated in the same way. The same racquet, the same string, and the same tension settings, and the same testing devices. I am not going into detail here because it is quite a lengthy path.

Here is what we need to know:
1. When stringing a racquet with main and cross strings, every racquet has a “natural ratio” of the final cross tensions to the final main tensions. That is what the cross string tension is relative to the main string tension of a finished racquet.
2. Nearly every machine tested allowed considerable distortion of the racquet in the three and nine directions. As much as .380 (9.62mm)! You want to minimize that distortion for the final strung racquet.
3. Almost every machine reacted slightly differently when the racquet was removed, i.e., some easier than others.

Why does this matter:
1. Due to the distortion, with the racquet in the machine, every machine produced main string only tensions of about 55% of the machine tension setting. That is the machine is set on 60 for example, and the measured tension is approximately 33 in the middle and increasing slightly going toward the 5th and 6th string. It never reaches 60 with only the main strings installed.

2. When the cross strings are installed, they begin to pull the racquet head back into shape but not significantly until nearing the 11th or 12th cross string.

3. When the racquet is finished and depending a little on the number of strings, it will, hopefully, return to close to the original unstrung shape and dimensions.

4. This “reshaping” can have damaging effects (stress failures) on the racquet.

Here is the question that started this whole discussion again.”

So, do I want to increase or decrease cross string tensions? My opinion is that until you know how the racquet, any racquet, is going to react don’t change tension settings at all. The key here is a responsible stringer wants repeatable metrics first.

We have an “Accuracy Index” procedure for every string pattern, that is the number of main strings and number of cross strings, that calculates the accuracy of the entire string bed based on where the ball is impacting the string bed. The accuracy index is a measure of the ball rebounding normally to a deflected string bed. For example, if a ball were to hit in the geometric center of an elliptical head racquet that was strung with main and cross string tensions that minimized racquet stresses and frame distortion the accuracy index would be 1.0. For the same racquet, if some of the strings were at low tensions (perhaps a break) the accuracy index would be less than 1.0.

Based on “observed breakage locations” we can see the accuracy of that small area of the string bed where most breaks occur.

Most machines I have evaluated will return accuracy indices of 87 to 95 percent.

I have, however, included in this test an “Efficiency Index” which shows me how much the racquet had to “move around” to achieve the accuracy index number and reach some equilibrium. This value is typically in the 70 to 75 percent range! So the racquet is working hard to get back into shape.

If you are a stringer or racquet technician, please note that after the racquet is setup in the stringing machine properly do not make adjustments to the supports during the stringing process. In some cases, the supports will not be in contact with the racquet. Don’t adjust.

Unless the racquet is mounted on a solid annular plate, like the top image, do not restrict the expansion of the racquet by placing a restrictive member across the 3 and 9 o/clock positions which in this image are the top and bottom.  The red knobs are the 12 and 6 o’clock positions

True Tension Professional

True Tension Professional Machine

baiardo

Wilson Baiardo

Yonex Protech 8 Contact Points

Babolat Racquet Station

Posted on February 10, 2018, in Learning, Technology, Tension, Testing Devices. Bookmark the permalink. .

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