Category Archives: Tension
Know Your String!
Several years ago, when we were beginning to increase the use of Ashaway MonoGut ZX and ZX Pro, it was not unusual to get a call from a client saying, “my coach says I should not be using polyester!” We could not agree more, and you are not using polyester!
You are using PEEK polymer! This string material was, and still is, referred to as Zyex with polymer production capabilities of Victrex in England.
Given the appearance of MonoGut ZX, Babolat Origin, and a few other non-polyester monofilament strings, it is not easy to distinguish these from stiffer polyester material strings. So know your string!
Single strand (monofilament) strings will have a gleaming surface unless they have been through a “roughing” process. So will monofilament strings of different materials. It is hard to tell just by looking, and that is what can create some confusion on behalf of the coach and subsequently, the player. So know your string!
If your racquet technician does not put a label on the racquet that identifies the material (or string), then be sure to ask what material you are using. The material choices may be natural gut, Zyex (PEEK), Nylon, and Polyester. The string construction may be referred to as a monofilament, multi-filament, single wrap, etc. however, the material will probably be one of these four.
Know your string! If you are unsure, contact your racquet technician or “Ask John” on this site, and we will try to help.
String Tension Testers…Friend or Foe?
The StringMeter is a device used to check the tension of an individual string. There are other versions of similar functionality, but this is what we use, and I will start with that.
Interestingly, this device traces its design to a tool that is used to check mainstay tension on a sailing vessel.
It is clear that our devices are well used, so they must be a “friend,” not a “foe”! And to that, I would say yes! The two (2) units shown here are “calibrated” units. One device is “free string,” and the other is “strung string.” These are different scales and very important for accurate information.
String Tension Tester
When we evaluate string or stringing machines, one of the most important values is the string tension with only the main strings installed. Using the “free string” scale, we check every main string and record the number.
Once the racquet is fully strung, we can check some center main strings and center cross strings with the “strung string” scale and see the variation. The difference between the two is the “natural ratio” of the racquet.
In addition to the stringing machine review use of the StringMeter, we also use it to calculate our “accuracy index.”
For this, we use the “strung string” scale and check each main string tension from left to right and every cross string tension from top to bottom and compare the actual numbers to the calculated numbers based on a non-distorted racquet. This spreadsheet shows how accurately the ball will come off of the racquet face.
The “efficiency index” tells us how much the racquet needs to change shape to reach that “index.”
These are all essential functions of the StringMeter and String Tension Tester from Gamma Sports.
But, what if the StringMeter or other device is used without knowing what it is telling the user?
This is the “foe” part!
This would be the case if a customer with such a device has a racquet strung at say a reference tension of 55 pounds. The customer then uses the method to check the tension and finds that it is not 55 pounds or even close! The customer is not going to be happy!
If the customer knows what to do, they can check the main string tension as soon as they can after stringing, then, later on, to see how much the string has stretched without regard to the reference tension.
It is what it is!
When the racquet is no longer performing it would tell the customer how much the tension can deteriorate before stringing is required.
So, these devices are very useful for individual string tension but no so much for “string bed stiffness,” which is the total string bed as a ball impacts it.
We will look at some of the “string bed stiffness” devices in a future post.
Racquet & Tournament Management
Management is not just for adults! Juniors that play tournaments need to have some management skills! During this coronavirus slow down it is a good time to learn some of these management skills.
We see many different management slip-ups such as no racquets for the tournament tomorrow! All racquets have broken string and are at the bottom of a bag nobody wants to stick their hand into!
Juniors Management Tip #1:
Every Monday takes every racquet out of the bag. If one or more are broken leave them out of the bag.
Juniors Management Tip #2
To get some idea of how much longer the string may last simply try to move the 5th or 6th cross string by pulling up toward the top of the racquet. If you can not pull the cross string up it is time for stringing. If you are able to pull a cross string up pay attention to the “snap” it makes as you push it back into location. A serious “snap” indicates a deep notch.
Monofilament strings typically fail by notching which makes it difficult to move the cross strings. If your string is a multi-filament and looks like the picture on the left it is time to string!
Abrasion Fail Visual Test
Notching Visual Fail Test
What if neither of these conditions exists?
Every racquet in your bag should have a tag indicating when the racquet was last strung and if it has been more than one month it is time to string, period!
Just for fun you can go to our SFC function and get a good ideas as to how many times per year yu need to have your racquet strung.
I Get It! Maybe… or Maybe Not!
When we do a racquet review we try to deal with numbers! Static and dynamic numbers to be precise. We do this so each racquet can be referred to by properties and not just by subjective comments. Make no mistake, subjective comments are good and can be used in fact to generate numbers!
Here is an explanation of the numbers and what they can mean to you.
It is well known that 5 players will have 5, or more, different “comments”, so having numbers provide a database, or history, of what works for what player style. With that information, a new client can be playing with their “perfect” racquet is a very short time instead of trying a zillion different models.
This is important because players may not be using the best racquet for them because they rely on assumptions instead of numbers! The very worst assumption is “I need a light racquet because I am just getting back in the game”. The second worst assumption is “I need a big head with a big sweet spot because I am not very good”. The third worst assumption is “I don’t need very good string because I am not very good”.
Bogus assumptions, every one of them!
As we look over our client data some things are clear and should become performance metrics;
- Total weight should be not less than 10.5 ounces (300 grams).
- Swing weight should not be less than 10.5 ounces (300 grams).
- Torsional stability should not be less than 15 units (typically grams).
With these metrics, you are off to a great start with a new racquet, or if you are beginning a new racquet search these numbers will be helpful.
By The Numbers
Here we go with this numbers thing, again!
Our Racquet reviews are a bunch of numbers, but what do these numbers mean to you?
We have put together this table with a brief explanation of how each number can be used by you to understand how that property can be helpful.
If you see terms such as typical or normal, ignore them! With tennis players, there is no such thing as “typical and normal”!
If you need to be convinced, take a look at a previous post!
Please let us know if there is a number that needs more clarification or a number we are missing!
| Manufacturer | Yonex | What it Means |
|---|---|---|
| Racquet Model | Yonex VCore Pro 97 HD | Racquet being reviewed. |
| Reference Tension | 55 lbs - 24.9 kg | Stringing machine tension setting. Not, necessarily, the string bed stiffness. |
| String | Ashaway MonoGut ZX Pro | String brand name and gauge (Pro being 17Gauge) |
| Machine Used | True Tension Professional | Stringing machine used. |
| ASPS, RDC | 56 | The stiffness of all the strings as a unit. Normally between 30 and 65. |
| ASPS, FlexFour | 64.5 | The stiffness of the string bed as tested on this device. |
| Racquet Flex, RDC | 57 - After stringing | 50 is low (flexible) and 70 is high (very stiff). Clash 100 is 52 on this device. As is a Head Speed model. |
| Racquet Flex, FlexFour | 50 | 35 is low (flexible) 70 is high (very stiff). Clash 100 is 26 on this device. |
| Racquet - In Plane Stiffness | 353.8 lbs/Inch | This is how stiff the racquet head is across the middle. 300 is soft and 500 is very stiff. This affects the string bed stiffness. |
| Weight, Grams | 336 | 285 is light and 360 is heavy. 315 is minimum target weight for performance. |
| Weight, Ounces | 11.85 | The racquet weight in ounces, typically used in US. |
| Balance, mm | 322 | This is the center of gravity from the butt cap. If you put the racquet on a round rod this would be how much is hanging toward the butt cap. |
| Balance, Inch | 12.68 | This is the CG in ounces for US. Points head heavy or head light is part of this. |
| Length, Cm | 68.5 | This is the total length of the racquet and is the typical standard adult length. |
| Length, Inch | 26.968 | This is length in inches for the US. |
| Head Width, Inches | 9.57 | The inside width of the hitting area. |
| Head Length, Inches | 12.54 | The inside length of the hitting area. |
| Head Area, cm2 | 625.8 | The advertised hitting area in centimeters squared. |
| Head Area, Sq. Inch | 97.0 | The advertised hitting area in inches squared. |
| Number of Main Strings | 18 | The main strings are the vertical strings when looking at a standing racquet. Typically the longest strings. |
| Number of Cross Strings | 20 | The cross strings are the horizontal strings when looking at a standing racquet. Typically shorter. |
| Ratio Cross/Mains | .687 | The natural ratio of the string pattern (calculated). |
| Main String Grid | 7.25 | The total distance between right and left main string. |
| Cross String Grid | 10.18 | The total distance between the first cross string and the last cross string. |
| Density (% of head filled with string) | .783 | |
| Average Cross String Space | .509 | The higher this number the more the string will move. This number is used to help select the best string setup. |
| Average Main String Space | .403 | The higher this number the more the string will move. This number is used to help select the best string setup. |
| Properties of a moving racquet. | ||
| Dynamic Tension, Kp, ERT | 37 | This is the stiffness of a string bed in kilograms per centimeter based on a frequency. |
| Dynamic Tension, Lbs/in | 206.94 | This is the above converted to pounds per inch. |
| First Moment, Nm | .831 | This is how heavy the racquet feels in the hand. The higher the number the heavier the racquet will feel. |
| Polar Moment | 340 | This is the resistance to rotating about the center of the racquet on, say a mimes-hit. The higher the better. |
| Torsional Stability | 16 | This is the derived stability number. The higher the better within reason. Anything below 14 would need some help. |
| Swing Weight, Kg/cm2 | 324 | This is the "inertia" of the racquet and probably the most important number in the review! The higher the number the more momentum through the ball but less manueverability. |
| Swing Weight, Ounces | 11.43 | |
| Swing Weight Calculated | 348.4 | This number will be larger than the previous swing weight because it is calculated from the very end of the racquet as if there is no one holding it. A very important number. |
| Power, RDC | 42 | |
| Control, RDC | 59 | |
| Manueverability, RDC | 71 | |
| Power, Calculated | 1740.5 | This number is calculated based on racquet properties. |
| Head Points | 6.46 (negative = head heavy) | This number is how positive or negative the balance is. A "point" is ⅛ of an inch so this racquet is a little over ¾ of an inch head light. |
| Head Weight, % | 47.0% | |
| Center of Percussion | 21.0 | This is the spot on the string bed that returns a solid hit. |
| Dwell Time, ms | 8.50 | This is how long the ball and string are in contact with no swing. A big swing will reduce this number by about half. |
| Efective Stiffness - lbs | 28.2 | This number is calculated from the string bed stiffness and the racquet stiffness. Anything under 30 will be "soft" feeling and over 35 will be "harsh". |
| K, Lb/In | 179.5 | |
| Recoil Weight | 160.8 | This number is the racquets resistance to rotating backward. The higher the number the better for volleys. |
| Twist Weight | 230.8 | This is the racquets resistance to twisting in your hand. The higher the better. |
| End Weight | 139.8 | This weight is used to calculate the precise balance of the racquet. |
| Tip Weight | 196.2 | This weight is used to calculate the precise balance of the racquet. |
| 9 O'Clock | 100.4 | This is the weight of that position on the racquet head and is used for precise customization. |
| 3 O'Clock | 99.6 | This is the weight of that position on the racquet head and is used for precise customization. |
| Butt Cap | 135.6 | This is the weight of that position on the racquet and is used for precise customization. |
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