Category Archives: Learning
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.
Racquet Quest sells only a few high performance racquet brands so it is not unusual for us to receive racquets purchased from on-line sources. These can be dropped shipped to us or brought in by the client.
That’s great. But here is the problem!
If you have a racquet technician in your neighborhood do not have the racquets strung by the online source! Take the racquet(s) to someone you trust, and, can be there if there is ever an issue, and this is an issue! The knot actually came untied! This is rare but is particularly likely when using a really “cheap” string and not knowing how to tie a proper knot!
Two things are happening here. The knot on the top is a “tie off” knot. While the tail may become loose it is not likely the knot will totally untie itself. The knot on the bottom is a “starting knot” and was subjected to the tension of the first cross string and, as you see, became a “not knot”.
This was very likely a “free” or “discounted” stringing so why not take advantage of the offer!
In this case, it is impossible to play with the racquet so what was saved by the cheap stringing?
This happens because the source knows that the racquet will probably not be returned for correcting the error(s) so who cares!
I care and you should care!
That is my “rant” for the day!
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
Racquet Quest, LLC, with the help of Dr. Rich Zarda and myself, invite you to meet us at the World Headquarter’s of Racquet Quest, LLC on Thursday, October 20th at 7:00 PM for an open discussion on tennis racquets, and, strings technologies. We expect to finish no later than 9:00 PM.
This first discussion is open to the first twenty (20) that respond, and, are attending. If this discussion is worthwhile, we plan on supporting larger groups in the future.
Racquet Quest, LLC is located at 3490 US 17-92, Casselberry, FL 32707, directly across from the Home Depot. You can find directions at www.racquetquest.com.
This is a “discussion” not a “sales” meeting, so your questions are solicited. If you want to send your question to me, email@example.com before the meeting date, please do so.
We will answer any prior questions at the discussion so everyone in attendance will hear the same answer.
Light refreshments will be served.
We look forward to seeing you here! Please RSVP with a phone number and/or email address. Time and space is limited.
Thank you for your interest…
It is easy for me to post pictures of racquets being made ready for shipment to tournament players. However, there is a lot more work before these can be tagged, bagged and packed!
Paperwork is what I am talking about! I have included some of the paperwork in this image, so you get some idea of what is involved. Not many people like paperwork but for this work it is essential!
Every racquet we do has the same “paperwork”, but local customers normally don’t need racquets customized and shipped overnight! Out of town customers, your racquets are typically prepared as close to the “use by” date as possible. So these racquets were strung and tweaked this morning and shipped (via overnight) this afternoon. Most of the customization can be accomplished before stringing but final adjustments, if required, are the last thing on the list.
The “paper work” on the right is data from the ERECA Balance System, and this information is taken at each step in the customization, and at a “play ready” status. While I still rely on swing weight as the primary dynamic property I use the ERECA system for very precise static balance, total weight, and a quickly calculated swing weight.
The other “paper” is my standard Racquet Record software data that contains over forty (40) pieces of data that are a permanent record in the customer file.
It sounds like a lot of paperwork, but it is necessary to assure consistency and organization. Every racquet gets the same treatment.
So, the next time you see pictures remember there is a lot more to it than stringing, bagging, and shipping.
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!
Has this ever happened to you? The string just breaks! For no reason, it just breaks!
Well, a closer look will tell a different story. The failure is referred to as a “mis-hit”, or “shank”, and is caused by hitting the ball at the junction of the string bed and racquet frame.
If look closely you will see a little yellow ball fuzz on the first broken string. So, if you are going to try to “sell” your story that it “just broke” be sure to clean off the ball fuzz before taking it back to the racquet technician. Keep in mind, however, that most racquet technicians have seen this failure before. Don’t try to fool them! 😉
All string materials are subject to this failure but some stand out as potential easy breakers. Thin gauge natural gut, probably the best racquet string ever, will fail at a load like this. Thin gauge PEEK string is likely to fail, as is some thin polyester based string. The point is almost any string will give up when encountered with massive head speed and a “mis-hit”.
As always be certain the grommets are in good condition especially around this area of the racquet.
We have talked about this before and by now we all understand “tolerance”, especially if you drive in this area!
We recently received fifteen (15) racquets from the manufacturer (A). The initial characterization was surprising in that the “tolerance” was very tight. In fact, there was only slightly greater than 3 grams separating all of them!
Later in the day I received three (3) racquets from the manufacturer (Z) and there was fifteen (15) grams difference between them (very “loose” tolerance). These were for a single player and needed to be matched for tournament play. It is obvious, then, that more time is required to match the three (3) than to match all fifteen (15) if the others.
This is not a criticism of the manufacturers only a glimpse of why some “customization” may be required to satisfy players needs. When a client calls with specifications for a racquet they are considering I always ask where the data is from. The “header card”, “on-line communications”, “other players”, etc.
If you rely on these data it may not be close to what the racquet will actually be when it is received.
Building a “custom” racquet is exciting not only because of the work involved but from the “joy” of the finished product!
When I receive racquets similar to the state shown the first thing that happens is numbering and characterization so it can be tracked throughout the process.
The first piece of equipment I use is the Ereca Balance System. Here is why. The two (2) scale system is fast and extremely accurate. This first “pass” tells me how much work is required to get the racquets to the customers specification.
These racquets had an average deviation of 1.69 grams! Other specs were also very close. Knowing this when I start the process means I can pick almost any of the racquets with confidence that I can achieve the desired “finished” specifications.
As you know I insist on swing weight as a major racquet property but this system gets me off to a great start and saves considerable time.
Each client has a specific specification they want in terms of length, swing weight, overall weight, grip size, grip material and where any modifying material, if required, will be added.
Adding string is a big factor because of the different weights of various string. Stringing is, typically, the final step in customization if any material is under the bumper guard
Custom racquets are not only fun to build they are fun to play with!
Many players simply don’t pay attention to the protection the “Bumper Gaurd” at the top of the racquet provides and, therefore, the racquet and certainly the string can be badly damaged!
When you see a grommet that looks like this it can lead to racquet damage as evidenced by the thin white line. This indicates the wear of a thin layer of graphite (what your racquet is made of) which, if left unattended, can lead to catastrophic ($$$) failure!
If you look closely you will see scuffing of the string which is now exposed to court scraping. What can cause court scraping? The primary cause is picking up the ball(s) using your racquet and your foot! This activity drags the racquet across the court hundreds of times and before you know it the string and racquet are runied!
I suggest you take a good look at your protection, and, if you are picking the ball up with your racquet, don’t!