Category Archives: Polyester
In dictionary terms it is:
“the amount of extension of an object under stress.”
In tennis terms, it means the same thing when talking about tennis racquet strings.
How much does a string stretch under the reference tension load or otherwise stretched (impact)? The proliferation of wrist, arm and shoulder injury has brought attention to the property of “stiffness.” The problem is that your stiffness may be different than my stiffness, so there needs to be an “index” associated with each string, in my opinion. I have that data on over 500 tennis strings, but that is just me.
The images show the results of high elongation (left) and low elongation (right) string upon breaking.
Several years ago a player asked me “where is the string that is missing?” Well, it is not missing. The ends you see should be connected!
If the string has little elongation when it breaks there is nothing “pulling” it apart like the high elongation string. So each time you hit the ball, the string either elongates a bunch or it doesn’t.
In the case of the high elongation string, on the left, it absorbs a good portion of the “shock” associated with a hard hit, whereas the low elongation string, on the right, lets your body do the absorbing to a great extent.
So, it is reasonable to use very low reference tensions for low elongation string (35 to 45 pounds; 16 to 20.5 Kg) and higher tensions (45 to 60 pounds; 20.5 to 27.2 Kg) for high elongation strings.
You may ask, “how do I know how stiff a string is?” If you see the word “polyester or co-polyester” it is likely that string wil be stiff compared to natural gut, most nylon based multi-filament construction, and PEEK (Zyex) material. In my opinion, there is no “bad” string just “bad” applications. If in doubt…ask!
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!
If you have been around Racquet Quest for a while, you know we talk a lot about Ashaway MonoGut ZX and ZX Pro, with ZX Pro being the 17 gauge version. During this post when I use MonoGut ZX it will include the ZX Pro Version, to save pixels!
A few questions need to be answered before we begin:
1. Do you get paid to talk about Ashaway MonoGut ZX?………. No
2. Do you get Ashaway MonoGut ZX free?………. No
3. Do get to spend the summer at a lavish resort in Ashaway R.I. ………. No
4. Why do you do it, then?
The short answer is MonoGut ZX works in so many applications that it is impossible not to talk about it whenever talking about tennis racquet string, arm issues, durability, and performance!
The first thing we need to know about MonoGut ZX is that is not polyester. It is Polyetheretherketone, or PEEK, for short. MonoGut ZX can look exactly like many common polyester strings due to the monofilament format. Monofilament means it is one strand of material and is typically very smooth and shiny.
The appearance is where the similarities end. Without going into a lot of detail, the stiffness of the base material dictates the stiffness of the string, especially in monofilament formats. Every string we get is tested for “stiffness” and entered into our database. This stiffness is converted to Power Potential using proprietary software. Power Potential is easy to understand…the higher the number, the more powerful the string is.
To get to the meat of this topic, we need to know the relative values of these materials.
MonoGut ZX has a power potential of 14.62
Babolat RPM Blast has a power potential of 4.29
LaserFibre Silverline 2 has a power potential of 4.59
Luxilon ALU Power has a power potential of 4.42
Luxilon ALU Power Soft has a power potential of 5.72
There are hundreds of polyester based string, but this gives you some idea as to where they stack up vis-a-vis MonoGut ZX.
Why does this matter? Strings with very low elongation (power potential) get stiffer the harder the ball is hit! So what? So, if you have low power potential, you need to swing harder to get the ball to go as far as it needs to go especially if you are trying to hit with huge topspin.
MonoGut ZX is suited to many playing styles, racquets, and string patterns. That is why so many really good players are currently using it and winning with it. That is why it is important that we continue to talk about MonoGut ZX!
Maybe it is time to try MonoGut ZX yourself.
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.
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?
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.
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.
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
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.