Category Archives: Tips
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
A client just sent me the following statement and I think it has reason to be distributed amongst tennis players searching for “direction” when it comes to string and their game!
“Hah. Trying out these different strings has been very interesting. Over the past week or so, trying the different strings has given me some insight into what my game should be. I think usually people do it in reverse. They try to find the string that tailors to their game. By experimenting with the strings, I realize the direction my game should be going.”
“I’ve been coming to realize that my game is better with control and feel rather than power. Experimenting with different strings have helped me recognize this.”
Do you think this applies to you?
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.
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.
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!
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.
When we think of “tolerance” we think of traffic, noise, and generally putting up with things, but normally we don’t think of tennis racquets!
However, we should! Tolerance means “what are the allowable variations between racquets of the same model”. Not all racquet manufacturers are the same but it would be a good guess the tolerance will be plus or minus 7 grams for example in total weight and maybe plus or minus 2 points for balance. A “point” is ⅛ of an inch so that is potentially a ½ inch difference! You can see in the picture why there can be variations. A lot of parts!
While “swing weight” is a very important characteristic it is difficult for manufacturers to match that so they will generally add a little weight in the rear end of the racquet to make the static balance the same.
In case you don’t recognize it plus or minus 7 grams adds up to about half an ounce!
For example one racquet can weigh 300 grams and another 314 grams with the specification of 307 grams showing up on header cards and advertising! Please know that racquet manufactures try their best to make all “performance” racquets the same. They do not purposefully make out of spec racquets!
But if they miss the mark…
This is where “customization” comes in handy. So don’t worry too much if your “tolerance” is “intolerable”. It can be fixed!
As a stringer you may, on occasion, clamp the string on the outside of the racquet frame.
This clamping can cause stress on the string right where it needs to bend or near the tie off area. This is not good!
The Offset Tube protects not only the racquet, but, more importantly, the string, by clamping about 2 inches away from the bending, or tie off, area of the string. The design and specific material properties of the protection pad assures proper protection without “tension loosing” softness.
This “quick and easy” to use device is a must for the serious racquet technician, and, if you are player be sure your “stringer” has an Offset Tube to protect your string!
The Offset Tube will be shipping starting the first week of November.
Each Offset Tube is $9.95 plus $2.00 shipping for up to two (2) in the US.
Your payment will be processed via our PayPal account but you do not have to have a PayPal account in order to pay. You can use any credit card.
As most of you know I am a big fan of Ashaway Monogut ZX (16g) and ZX Pro (17G) string. These models are PEEK mono filament strings that resemble polyester strings but these contain no polyester!
Here is the latest PR from Ashaway for your review.
Please let me know if you have any questions, and of course if you want to try this string.
Why did my very expensive gut string break when I wasn’t even using it?
You open your tennis bag; pull out your favorite racquet, and…what the heck, (or something like that)!
Natural gut is still considered the best of all string materials and performs beautifully in most racquets. However, natural gut is pretty expensive at about $70.00 per set, installed.
So, it makes sense that one would like for it to last a long, long time, and, of course play well for that entire time.
The perfect failure is when the string breaks around the middle of the string bed, then, why, when you pull the racquet out of the bag, the string is broken at the top and/or bottom!
If you look at this failure you will, or should, notice where the string breaks. The first reaction is “the grommets are bad”. This is not the case here. But why does this happen?
We need to understand a little about the racquet instead of the string right now.
The strongest, and stiffest, portion of the racquet is where the throat piece joins the head shape.
When the string is installed in this area it is “tighter” than the other strings. That is number 1. Number 2 is that natural gut string “moves”, actually contracts and relaxes, quite a bit, naturally. When natural gut moves, especially in this area, at the top and bottom, a lot of stress is caused at the bending points, which can contribute to the failure!
So, the string in that area is stretching and relaxing over and over again until it cannot endure and simply breaks!
So, what can you do to mitigate this failure mode?
- Avoid huge and sudden temperature changes.
- Consider tension changes on strings in this area
- Consider thicker natural gut string. Use 130 instead of 125, for example
- Avoid really wet conditions
- Be certain the string is installed using the appropriate “care”
Natural gut is good…