Category Archives: Tension

This is Important!

I was just going through some older posts and came across this “E” Book post and believe it is more relevant now that when I originally posted it!

Take a look because this is important!

What is Soft…er?

Our Standard Stringing Process

After seeing “After the String is Strung” some of you wanted to see a “While the String is Being Strung” video.  I have several videos of the stringing process but I use them for my own review and to see if there is anything that can be done better.

So, the video(s) will not be “professional” videos and are intended for fun and maybe some understanding of what we do.

Grab a coffee, or something, and enjoy 24 minutes of stringing fun!

What is “Best Overall Performance”?

In our “Recommended Stringing Frequency” calculator we state that this frequency is to get the best possible performance from your racquet.   But, what exactly is “best performance”?

To establish this we need to take you, the player, out of the picture for a moment and concentrate on the racquet and string setup.  the reason is simple:  no two players strike the ball the same way.

We start with “Swing Weight” which is the most important dynamic property of a racquet.  So a higher swing weight will contribute to power and stability, thus performance.

Overall weight is important because you need to be able to get the racquet to the court and out of your bag!  Heavier racquets contribute to energy, stability, and comfort.

Effective Stiffness is important because it represents the stiffness of the string bed (SBS) and the racquet stiffness (xxRA, or something like that).  This number represents the impact each time you strike the ball.  The higher the number, the stiffer, of course.

Of the four (4) things mentioned above we can control the string bed stiffness with ease.  One of the easiest methods is to string your racquet regularly to maintain the effectiveness of the elongation of the string being used.  Elongation relates to energy return in a string and while strings will stay resilient for a long time a well-worn string takes a while to return energy to the ball.

You, the player, of course, determine performance so when using the SFR you can enter a high UTR or Style rating or a low UTR or style rating if maximum performance is not required.

After the String is Strung!

I have often wondered what players know about the “stringing” process and in particular what goes on after the “string is strung”.  So, while Madelyn was here she decided to video me doing what we do after each racquet is strung and just coming off the machine.

Had I known we were going to do this I might have dressed up a little, emptied the trash and fixed the crack in the wall behind the RDC!  But I didn’t.

This video is offered as a “real-time” view of what we do with every racquet and is intended for information and fun only.  If you have any questions please let us know…now enjoy the movie!

And Now This…

In the words of Lord Kelvin (May 1883) “When you can measure what you are speaking about, and express it in numbers, you know something about it, when you cannot express it in numbers, your knowledge is of a meager and unsatisfactory kind; it may be the beginning of knowledge, but you have scarcely, in your thoughts advanced to the stage of science.”

That is why every racquet we do has over fifty (50) numbers attached to the finished data. Most of these numbers will remain unknown to the client, but for us, it is imperative that we know them.

Numbers Matter!

Which leads me, again, to this very important discussion.

Every day we see a statement from tennis string manufactures claiming, or suggesting, their string is the “softest ever tested” and other claims.  What the heck is “soft” anyway?  There is a lot more to it than meets the eye so we have done significant analysis on bunches of string and can now quantify “soft” as it relates to tennis string.

What is “soft”?
In 1994 I did a presentation for the USRSA in Atlanta. What was the topic?

“Understanding String.”

It is now 2016, and we are still trying to understand string! Especially “soft” polyester based string.

In 1994 PolyStar was the only polyester based string I was familiar with. Since then there are dozens of offerings from anyone that can afford to purchase from manufacturers and market the string. If you have a desire to do it, I applaud you!

In 1989 I started testing string and calculating “power potential.” Why “power potential”? Because “modulus,” “elongation” and “elasticity” didn’t get to the bottom line of string performance quickly enough! The steps to arrive at power potential are many.

For the testing, several calculations take place including “stretching” the string as in a ball impact. The difference between the first calculation and the “stretched” calculation is the power potential!

I have calculated hundreds of power potentials but have not until now quantified “soft.”

I think now is the time!

Under the direction of Dr. Rich Zarda, we have done a tremendous amount of work on this issue so we can now distill this work into the following explanation.

So, what is a “soft” tennis string?

Strings in a tennis racquet carry the ball impact load in two ways:
1) Via the pre-load string tension placed in the strings caused by a stringing machine (and the racquet frame “holding” those tensions in place) and
2) Via additional tensions that develop in the same string caused by the elongation of the strings as they deflect with ball impact.

Both of these conditions occur simultaneously and contribute to the string bed stiffness (SBS, units of lbs./in). Racquet technicians measure SBS by applying a load to the center of a supported string bed and measuring the resulting deflection. Dividing the load by the deflection provides the SBS (lbs./in). The lower the SBS, the more power you have (power here is the ability of the ball to easily rebound from the string bed), but the less control (presumably); the higher the SBS, the less power you have but, the more control you have (presumably).

One more point about SBS: the lower the SBS, the less the load your body will feel for a given swing. But for an SBS too low (less than 50-80 lbs./in), balls will be flying off your racquet going over the fence; and for an SBS too high (greater than 200-240 lbs./in), the racquet will hit like a board with significantly less ball rebound. So the most common SBSs are between 100-200 lbs./in: a balance between control and power.

As already expressed, SBS is a function of the pulled string tension and the string elongation. Here is what is interesting: For large string elongations (for example, greater than 15%) and reasonably pulled string tensions (greater than 30-40 lbs.), SBS only depends on the pulled string tension, and it does not depend on string elongation. Additionally, for this condition, SBS, for these high elongation strings, does not change as a ball is hit with more impact.

linearity_noname

But for a string bed with low elongation strings (less than 5%) under low pulled tensions (less than 20 lbs., or tensions that have been reduced due to racquet deformation and/or string tension relaxing with time), the SBS additionally depends on the string elongation and will significantly increase, in a nonlinear ever-increasing way, for harder ball impacts.

In order to achieve a repetitive feel for a player when hitting with a racquet, it is best to have an SBS that is independent of an increasing ball impact force. This will lead to a more consistent playability of the racquet, which includes a more repetitive feel. This desired “feel” implies using high elongation strings (greater than 10%). If low elongation strings are used (less than 4%), the SBS will significantly increase as the ball impact force increases, resulting in a racquet feeling “boardy” for higher impact loads. And low elongation strings will cause un-proportionally increasing load into the body.

deflections

As you can see by the graph, elongation contributes to SBS in a big way. The red line indicates a stiff string, about 4%, and the blue line indicates a “soft” string, about 15% elongation. You can see the loads increase dramatically as the impact increases. So the harder the hit the higher the loads on the body.

So to the question asked at the start “What is a soft tennis string?” In the context of the SBS discussed above, I would suggest that a soft tennis string is one whose elongation is 10-15%, and a stiff tennis string is 4-6%. And any string under 4% should be categorized as ultra-stiff.

String elongation (soft, stiff, ultra-stiff),  stringing machine strung tension, and string pattern(s) all contribute to SBS and SBS is an important measure of how a racquet plays and should be adjusted for an individual player, stiff and ultra-stiff strings can lead to less-repeatable racquet performance and player injury.

Soft = 10 -15% Elongation                Power Potential Range = 10.0 – 16.0
Stiff = 4 – 6% Elongation                   Power Potential Range = 4.0 – 7.0
Ultra Stiff =  Less than 4%               Power Potential Range = .65 – 3.96

 

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

Shaped String Considerations

Monofilament string can be easily produced in almost any shape.  Round, square, triangular, hexagonal, octagonal etc.  So, on the surface that seems like a good thing.  Who wouldn’t want the sharp edges digging into the ball creating even more spin!

But, there may be a side to the shape that needs considering and that is tension as it is applied to the string vs tension as it is in the racquet.  Those can be two very different things!

When the main strings (the long ones usually) are installed they are free to move and will normally be only slightly “twisted”.  This is more obvious with square and triangular strings.

Cross String Twist

This image shows one of the lower cross strings and the “twist” is obvious.  So what?

So the tension on these strings will be considerably lower than expected.

Why?  The machine tension head is set to pull each string to the desired setting, say 50 pounds.  When the machine “feels” 50 pounds the tension head stops.  The cross string will twist, just like a screw, as it passes over and under the main string.  A twisted string will not pull through the adjacent main strings easily so the tension will, in this area, be less than desired.

This variation in “tension” can affect the way a ball comes off the racquet.

We use string spreading devices for every racquet and every type and shape of string.  The “spreaders” raise and lower the main strings so there is no friction (twisting) between the cross string and the main string.

Not all racquet technicians use this type of device, so,  the twisting can be mitigated by weaving the appropriate cross stings over and under the main string one at a time making sure they are not twisted and then apply the machine tension.  This will result in a more consistent result.

If your racquet has cross strings that look like the image be sure to mention it to the stringer so it can be remedied.

 

What is Important?

I spend hours each day dealing with tennis racquets, strings, machines and questions of all sorts!

By doing this I am learning what is important to tennis players but it should not require a one-on-one discussion to learn this, in my opinion.

So, what is important to you?  Here is what I am discovering.

Comfort.  It goes without saying that you don’t want to play tennis if you are hurting!  Players are requesting racquets that are more arm friendly.  But wait, the racquet really holds the string which has a huge impact on comfort.  So should we begin with string?  I think so!

String.  Every string I have has undergone a comprehensive testing procedure to determine elongation which in turn is converted to Power Potential.  The higher the elongation the higher the power potential and the less stiff the string bed will feel when the ball is hit hard, all other settings being equal.  If you have a stiff racquet it is important to select a string and tension that will mitigate the racquet stiffness to some extent.  Every racquet we do has the “effective stiffness” calculated which is the combined stiffness of the racquet and string bed. Once we have the preferred effective stiffness for a customer we can achieve that even if a new racquet is added to the mix.

Durability.  We try to associate the cost of racquet stringing to “cost per hour” of play time.  What is your threshold?  $1.00 per hour or $10.00 per hour?  When considering durability do not confuse “performance” with “durability”!  There are several strings that may not fail for several months however the performance is gone in a few hours.  This is typical of polyester based strings.  So, even if the string is still intact the performance is way gone!

Cost.  The cost of tennis racquets is increasing, sometimes justified, sometimes not but are rising none the less.  If cost is your “driver” some navigation around the market is important, however, we do not suggest you buy the “cheapest” thing you can find without a thorough understanding of what you are getting.  We can assist you in evaluating racquets from any source.

Is This the Perfect Combination?

It seems like Ashaway had this very racquet in mind when they developed their Dynamite Soft 18 string!  This blue string is a perfect match to the blue accent color on the Ultra 100 CV and Ultra Tour!

And, the gauge, a very thin 18, is a perfect match to the very stiff frame (73 RDC, 70 FF stiffness).

I think the 18 gauge string may not be durable enough for hard hitters but this combination could be very good for many players.

You can be the judge of that, of course.

The string tension of 48 lbs (21.7 kg) combined with the racquet stiffness returns an effective stiffness of 30.3 which is a very comfortable number.

This stiff, 100 square inch racquet, should pack a powerful punch with a weight of 318 gr (11.2 oz) and swing weight of 318 kg/cm^ (11.2 oz).

Hybrid Stringing…What is it and Does it Matter?

When the discussion is about stiff polyester string, it will always include the word “hybrid”!  Typically this word is used to convince players that by putting a “soft” multi-filament string in the cross position the string bed will be easier on the wrist, elbow, and shoulder.

Intuitively this makes sense, but in reality, the reverse could be true!

I began analyzing hybrid string beds years ago and did many just to test the theory. At the time it did not seem so important because, frankly, the use of polyester based string did not approach the usage of current times.

I have nothing against the polyester string(s)! I do have an issue with bad applications of polyester string(s).

I am bringing this up again because recently an “interviewee” stated that that replacing the polyester cross string with a multi-filament would cure the ills of a very stiff string bed.

The bottom line:

A high elongation string of any material can increase the string bed stiffness of a hybrid string bed!

How can this be?

Stiff (polyester) strings are “stiff” and the tension applied to them during stringing is low. However, high elongation (multi-filament) strings will be influenced more by tension and become “stiffer”.  The cross stings are typically shorter, and there are more of them, so the combined affect is stiffness.

The initial reaction to this conundrum is to automatically reduce tension on the cross string by a certain amount. Again this raises another issue, and that is racquet distortion.

During the installation of the main strings most stringing machines will allow the racquet to become wider, sometimes a lot wider! So, reducing the cross string tension may not return the racquet to the designed shape. What happens then is the racquet will continue to move around trying to find a “safe” place and therefore the string bed stiffness changes.

In summary, the hybrid string bed will not be statistically different than the full string bed of polyester. This is even truer if the initial string tensions of the polyester are very low, such as 35 to 40 pounds.

So if you feel the need to use polyester just go with lower, lower,  tensions.

 

 

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