Category Archives: Testing Devices
If you have been following Racquet Quest online and with the podcast, you know we are very fond of data! In keeping with that “fondness,” we have received our newest testing device, which I have named “Questron.”
During the last week, we have spent time getting Questron set up to do the kinds of testing we think is important for the tennis player, the racquet technician, and anyone else that cares about numbers!
It will be about another week before posting any data because we are “tweaking” some connection points, cycle settings, and refining the data’s graphing.
We have over 400 strings to test; however, we will eliminate many of those strings not relevant to today’s tennis player.
Even in the “testing” phase, we are discovering interesting facts about strings that will help us put together the best setup for you!
This is the “base” Questron. Future versions of this device will incorporate the “Power Potential,” “In-Plane Stiffness,” and “Dynamic Stiffness” testing that is currently done on other equipment.
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.
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.
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!
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.
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, 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".|
|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.|
2019 came and went in a blur! In a few days it will 2020 and with it will come some exciting new tennis stuff, for sure!
I am not so good at predicting things but I do it anyway! Here are a few predictions I will make for 2020:
- Tennis racquets will become more expensive, but only slightly.
- On-line sales of tennis racquets will increase. See this previous post.
- Customer satisfaction with on-line sales will decrease.
- Small specialty tennis shops will be the source of information, then #2, and then #3.
- Players will stick with a racquet longer, making customizations as needed.
- String and stringing will become a more important component of a racquet purchase. See below!
- Tennis related injuries will continue to be a problem for the sport going forward.
Thank you for thinking about the “long term” for all tennis players!
There are no bad strings just bad applications!
The right equipment is crucial to the long term enjoyment, and winning, of tennis!
The local representatives I deal with are committed to our “well being” even though some may feel like they are facing “extinction”!
An excellent example of what we are talking about just walked in! Two (2) new racquets so poorly strung it is shocking!
The customer is having serious arm issues with an excellent racquet, with a terrible string setup! But the string setup is probably considered by many to be the ultimate combination, that is RPM Blast in the main and VS Touch in the cross! That combination is coming out in a few minutes! No more polyester!
The quality of the stringing is what is so wrong! Had you or I received this racquet, we would have returned it at once! Why? Because it exemplifies the attitude of so many stringers that is “who cares”!
Happy New Year!