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What is “Soft”?

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!

Dr. Rich Zarda has 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.


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 a 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.


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

A Word About Racquet Record Software

In 1999 I developed Racquet Record for the PC platform and used it in a technical retail environment.

In 2008 I moved to the Mac platform and developed new software that included more formulae/calculations based on years of research.

Recently the support team for Racquet Record ceased to exist therefore I have determined that the proper support for Racquet Record is not possible so I will not be offering the software for sale.

A recent article in Tennis Industry magazine, based on an “Internet search”, references Racquet Record software, for which I thank them. The publication was not aware of my decision. If and when I believe support is available I may re-think this decision.

I thank all of you that are using Racquet Record and I will offer as much support as possible.

Racquet Technician Software

Well, it only took a little over two (2) years but the new RacquetRecord™ is now available for users of the MacIntosh and Windows operating system! I made the move to Apple a few years ago and appreciate the “usefulness” of the system so it took a while to get the PC version to market.

With RacquetRecord™ I tried to continue with that “ease of use” functionality.

RacquetRecord™ includes dozens of fields that are designed especially for the serious racquet technician, including client and technical racquet data.  Work Orders, Worksheets, Invoices, and racquet labels are easily printed.

RacquetRecord™ is not a “financial” application but includes totals for each racquet strung and “total” reports for year end records.

The cost of RacquetRecord™ is $79.00 for a version without data and $94.00 for a version that includes some product data, and is downloaded to your computer.  You can take advantage of a ten (10) day trial.  When you purchase RacquetRecord™ a serial number will be sent to you.

Additional functions have been added so the homepage of your version may not look exactly like the image above.

I have kept the price as low as possible so every serious racquet technician can begin to realize perfect organization of the stringing business.

RacquetRecord™ Software

Thank you for your interest in RacquetRecord™ Software but we no longer sell or support RacquetRecord™.

String. What is important?

The essential function of string in your tennis racquet is to return energy to the ball as it collides with the racquet. It is evident that if there is no string or a broken one, the racquet can not do what it is intended to do, and your shot is going nowhere or worse, everywhere!

There are about thirty (30) string brands, and each brand has about ten (10) different models, and maybe three (3) different colors, so there are nine hundred (900) possible selections! Nine hundred is way too many strings!

You and we need to consolidate string data so we can make the right decision for you, your playing style, and your physical capabilities.

We test every string for elongation, creep, (stability), with a little bit of elasticity data observed. This testing returns our exclusive Power Potential© for each string, and that is the basis of our decision-making process. Naturally, the higher the elongation, the more power the string will return to the ball, and conversely, the lower the power potential, the less power that “can” be generated. You can observe this fundamental by dropping a tennis ball on a concrete floor and then on a strung tennis racquet from the same drop height and see which one bounces the highest.

I use “can” because power, to a great extent, comes from how hard you swing the racquet, which, of course, brings the prospect of overdoing it and subsequent injury! A low power string demands a more powerful swing that involves the entire arm, hips, and legs.

Low power, in the form of a stiff string, has been associated with control, therefore, the increased use of stiff strings. However, with stiffness comes another downside, and that is stability. Stiff strings typically lose tension quickly and need to be changed frequently. So here is the real problem; the string may not be broken, but it is not playing well at all. There is a difference between durability and performance! If your goal is long term performance, a stiff string is not the answer.

What, then, is the answer?

Choose a string with an elongation of 10% or higher! Oh, great! You say. How am I going to know that!

Well, beginning January 1, 2020, I will be posting the power potential of every string we have tested over the years! There are over 500 items on the current list sorted by brand. The color coding is RED if 5% or less, GREEN if 10% or higher, and BLUE for everything else. Note, however, that natural gut is included in this data and will probably not reach the 10% Power Potential© threshold, but is still the best performance string available.  This is due to the dynamic properties of the natural fibers, so, until there is a separate classification gut will be included as is.

A previous post, “What is Soft?” goes into graphical detail.

As new strings are added, some older ones may be deleted because they are no longer manufactured. However, some very old ones may remain due to their “legacy” status. This chart is a preliminary format but will get us map toward the right decision!

Click here to see all the current power potential data.