Category Archives: Distortion
We all know what friction is. It keeps our cars from sliding around, it keeps us from slipping and in general makes movement possible!
Friction also plays an important part in the string bed of your tennis racquet. Friction between the strings and the ball create friction which in turn creates rotation.
What are, however, some of the downsides of friction in the string bed during, and after, the stringing process?
For more detailed information and a graph showing the forces involved go to our membership site, GASP.network, but in the meantime this image will show the frictional forces at work!
This machine tension head will pull the string (blue) in the direction of the center of the racquet support structure instead of directly out the middle of the grommet.
It is obvious that this will create considerable friction and result in lower tension inside the grommet than outside the grommet.
It sure sounds simple but is it? Not really! When talking about tennis preparedness that means having enough racquets ready for the tournament, organizing training sessions, plenty of shirts, shoes, and socks, of course!
But, what’s missing?
Your string is missing! Sure, you have done a great job of getting your racquets ready but I don’t see several sets of the string you use in the bag! Why not? You may believe they will have it at the tournament site, and, if you are using a commodity string, you may be right!
But what if you’re using a high performance string that is set up for your playing style?
- Take a few sets of your preferred string with you. I prefer sets over reels but that is up to you.
- Tell the stringer exactly what you want. That means knowing what you want so be prepared!
- Request that your racquet be strung using two (2) pieces of string and the cross strings be started at the top of the racquet. No exceptions! No ATW’s, No natural one-piece, simply two pieces top to bottom!
Know how to identify the correct stringing procedure and don’t accept anything that is not up to your standards!
Most qualified stingers will appreciate your input and do the proper job for you!
Today a racquet came in that was strung at a tournament that missed the mark! One-piece ATW, sloppy knots, distorted head shape, and a string that is not used by the player!
That is why we are posting this… “Be Prepared”
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.
When we do the testing and “number taking” for our demo racquets, we try to think as the consumer may think and include comments that may help the consumer make the best decision.
We do not want to make these posts so dull that you go to sleep, but data is essential, so we are going to include it…so stay awake!
Data is particularly relevant to the Prestige Series from Head.
This review is for the Prestige Tour, and it points to the differences between Prestige racquets that may go unnoticed or misunderstood.
The Prestige Tour is a 99 (645 cm²)square inch racquet with an 18 x 19 string pattern. If you have read the post on the Prestige MP, you may wonder, what’s the difference?
You may notice that the Prestige Tour has one (1) fewer cross string. Not a big deal. You may see that the Prestige Tour has one (1) square inch larger head size. Also, not a big deal. What you may not notice is the Prestige Tour has an in-plane stiffness of 400, and the Prestige MP has an in-plane stiffness of 359. That is a big deal! Even with a bigger head and fewer strings, the Prestige Tour has a higher string bed stiffness than the Prestige MP. The higher the in-plane stiffness, the less the racquet will “bend” during impact.
The Prestige Tour is more stiff overall (62 v 58) than the Prestige MP, and the 21.5mm beam contributes to that stiffness.
So, take a look at the numbers for this racquet to see if you can find other exciting differences!
Racquet Model Head Graphene 360+ Prestige Tour
Reference Tension 55 lbs - 24.9 kg
Victrex PEEK fiber Experimental 7718
Machine Used True Tension Professional
ASPS, RDC 55
ASPS, FlexFour 71
Racquet Flex, RDC 62 - After stringing
Racquet Flex, FlexFour 49
Weight, Grams 325
Weight, Ounces 11.46
Balance, mm 327
Balance, Inch 12.87
Length, Cm 68.6
Length, Inch 27.008
Head Width 9.56
Head Length 13.12
Head Area, cm2 635.3
Head Area, Sq. Inch 98.5
Beam Width, mm, Shaft, Center, Tip 21.5, 21.5, 21.5
In Plane Stiffness, Pounds/In 400.0 Lbs/In.
In Plane Stiffness, Kg/cm 181.4 Kg/cm
Number of Main Strings 18
Number of Cross Strings 19
Ratio Cross/Mains .690
Main String Grid 7.81
Cross String Grid 10.00
Density (% of head filled with string) .724
Average Cross String Space .526
Average Main String Space .396
Dynamic Tension, Kp, ERT 35
Dynamic Tension, Lbs/in 195.7
First Moment, Nm .819
Polar Moment 334
Torsional Stability 18
Swing Weight, Kg/cm2 316
Swing Weight, Ounces 11.15
Swing Weight Calculated 347.5
Power, RDC 46
Control, RDC 55
Manueverability, RDC 76
Power, Calculated 1929.2
Head Points 4.88 (negative = head heavy)
Head Weight, % 47.7%
Center of Percussion 20.8
Dwell Time, ms, No Swing 8.58
Efective Stiffness - lbs 29.1
K, Lb/In (SBS) RDC 176.3
Recoil Weight 150.9
Twist Weight 222.7
End Weight 131.7
Tip Weight 195.3
9 O'Clock 100.7
3 O'Clock 101.4
Butt Cap 124.0