Category Archives: Juniors
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!
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
I posted recently the sad results of a mis-hit but I don’t think that term has been properly discussed. So, let’s talk about it now.
In the post I also mentioned the word “shank” and in fact, that may be more descriptive of what happens.
Mis-hits or Shanking is the “hard” collision of the ball hitting the string and the racquet frame at nearly the same time. This impact causes huge shear loads, like a scissor, and is accompanied by an “impulse”. That means the load is applied over a very short time period, or, in other words, a sharp blow.
A reasonable question, then, is “why does it usually break around the top of the racquet?” The short answer is that the top of the racquet is moving faster than any other part of the racquet with great leverage , therefore, the load has no place to go except into the string. If, however, the mis-hit occurs around the side of the racquet it can “rotate” in your hand and mitigate the load. That is why we see very few failures around the side of the racquet.
I have found that most mis-hits happen with younger players that are very aggressive naturally and are, at the same time, experimenting with different strokes, serves, grips, and spin. All of these things can cause mis-hits and the string failure associated with them.
In most cases mis-hits can be eliminated, by the player, through concentration on impact location, such as trying to hit the center of the string bed, however, on occasion, seldom I hope, the concentration is not there or the desire to return a shot takes precedent over concentration!
As you know I do a lot of string evaluations for myself, my customers and some manufacturers. I do this to have a clear understanding of what a string does at various tensions in various racquets ,and, also in a “controlled” environment!
So, if you ask me for a recommendation my answer will based on data, and, of course some anecdotal evidence. I know most manufacturers try very hard to place the string into the correct category but sometime they simply miss!
There is an ongoing conversation(s) regarding the categorization of polyester based strings relative to racquets and player stature. This may, for example, look like; “If you use Racquet “X” and are under fourteen (14) years old do not use “XYS” string at tensions higher than 40lbs (18.1 Kilo)”.
It is well known that it is very “tricky” to use polyester based string for most younger players that are experimenting with stroke production and still do not have the physical strength to really take advantage of what polyester may offer. For the record I do not recommend it.
Durability is always an issue so when I ask for “playing time” it should be in hours, not days or weeks, but hours. It is a big help to know what portion of those hour are training or playing. It is obvious that one (1) hour of training will be more “destructive” than one (1) hour of tournament play.
The more we know about string the better the choices can be. It is my imperative that the string matches/enhances the application. Tennis Warehouse, the premier online source for tennis stuff, is also very active in the effort to enlighten players in the selection of the string they order. We can do this!
What do you think?
The “Eddie Herr” is the largest Junior international tennis tournament in the world, and Jack Anthrop is ready for the Eddie!
Jack is using a Head Graphene XT MPA (16×19 format) fitted with Ashaway Monogut ZX. Jack has been using this string for several years and is having really good results as evidenced by his main draw selection into this tournament!
Good luck to Jack, and Maya, (don’t have a picture) and all the participants from all over the world, in this very important tournament!
The Eddie Herr International Tournament is held at the IMG facility in Bradenton, FL beginning November 26 and continuing through December 6th. This tournament has been the “springboard” for players like Roger Federer, Andy Roddick, Maria Sharapova and many other professional players over the years.
No, this is not about cheating! At least on-court cheating.
This is about cheating the players that have their racquets strung at tournaments!
Tournaments are tough enough on parents due to travel, scheduling, equipment, and racquet stringing. Many times the player must have a racquet, or racquets, strung during the tournament. If, and when, the racquets return to me I see, in too many cases, they are not getting their money’s worth! They are being cheated!
The problems range from poor workmanship, bad knots, cross-overs, to incredibly inconsistent string beds. Inconsistent string stiffness from side to side and generally too “soft” or “hard” string beds are common as well as serious racquet distortion.
Does this mean the player is going to loose? No, of course not,but it is not giving the player the best performance they, and their racquet, are capable of.
I know the cost of stringing at a tournament is generally not “too” high but not getting what you pay for is very expensive. These poorly strung racquets need to be re-done and that is an additive cost that makes playing tournaments even more expensive.
I urge that tournament directors, parents, and players demand better stringing at the tournament site. And, if the racquet is not properly done it should not be charged. The problem is the person picking up the racquet may not know if it is right or wrong, good or bad!
I know some of these “stringers” try very hard but they may not have equipment required to affect a really good result. Other “stringers” simply don’t know, or care about, what they are tasked to do. It shows!
Players: make sure your parents know you need racquets strung before you go to a tournament.
Parents: have as many racquets as possible prepared by your regular racquet technician before the tournament. This can actually save some money!
Players: don’t accept racquets that are not properly done. Don’t blame the racquet for poor performance if you accept it!
Parents: don’t pay for racquets that are not properly done. Let me know if you are not sure what to look for.
Parents: take at least three (3) racquets to every tournament.
Parents: if you think you are not getting the quality you deserve send me the tournament name and I will reach out to them and suggest they attend the Annual IART Symposium where all stringers learn how to do a better job…for you!