Category Archives: Tension
Our Questron in Action!
As you know, Racquet Quest is a data-driven business, and data requires numbers. To generate those numbers, we have designed and built several devices.
One device is the Questron!
The Questron is used to test every string we receive, and the data is compiled to understand where that particular string fits.
So, instead of talking about it we have included a short video!
Thank you for watching our Questron in Action! If you have a question, or a particular string of interest, please let us know. We may have already taken the data! On GASP.network there are many graphs of previous tests. GASP.network is a membership ($40.00 one time) site.
What’s The Difference?
As tennis players, you must constantly ask “what’s the difference” when it comes to tennis racquets and string! Well, as racquet technicians we ask the same questions!
This post is intended to showcase the differences of string in testing, not playing, however, some of the data may be noticeable to the player in certain situations.
What this graph shows us, in addition to our trying to save a tree by printing on the back of previously used paper, is that each of these stings will provide almost the same performance. This is indicated by the curve and how closely related the strings are.
Tensile Strength Comparison
The differences you do see here can be attributed to the gauge, or diameter, of the string, with the largest diameter (Tour Bite) having the highest tensile strength. Down in the “hitting” displacement range (way below the 39.9mm!), there is very little difference.
The tensile strength can be a factor as the string begins to “notch” or otherwise come apart. Each of the strings in this graph is monofilament so notching would be the failure mode in a racquet.
What Can Pictures Tell Us About String?
It is said that “a picture is worth a thousand words,” which may be true as long as the picture tells a story.
This story is about natural gut string, and the pictures will show what we can achieve, informationally, with our testing equipment. The two (2) strings are Babolat VS Touch 17 and Luxilon Natural Gut 125.
Our Questron software scales the images to suit the data so the graphs will not be the same size.
Babolat VS Touch 17
Our testing loads the string from 0 pounds force to 50 pounds and back to zero then up to 50 pounds three (3) times. This is the “stress/strain” curve. Fifty (50) pounds is arbitrary and because we are using the same methodology for all string materials it is a good number. The closer these lines are together the better.
The farther it takes to reach 50 pounds the “higher elongation” the string is. In this case it is about 44mm.
The important property of this string is the linearity! That is the “straightness” of the line from beginning to end. This indicates predictability, stability, and consistency.
This picture tells us the tensile strength and the knot strength. In this case the knot strength is 52.3 pounds and takes a stretch to very close to 60mm before failure.
Luxilon Natural Gut 125
What is, probably, the first thing you notice about this “picture”? Could it be the squiggly lines? What could be causing this?
We believe it is the “break-in period” players associate with Luxilon gut! We have heard it from the players but have not been able to “see” it! It could be the bonding agents realigning as the load is applied.
You will notice a couple of things: the similarity of the “stress/strain” curve and the displacement to “knot strength” of the two strings. This string will feel a little less “soft” than the Babolat VS Touch 17. The linearity is quite good up to failure.
So, based on these pictures, could you make a recommendation? If so, let us hear them!
And the winner is…Head FXP 17
Head FXP is a string that seems to be largely overlooked and I am surprised after seeing the results of the installation and testing!
| String Name | Category | Gauge | Ultimate Tensile Strength/Lbs | Knot Strength/Lbs | Country of Origin |
|---|---|---|---|---|---|
| Head FXP | Multifilament - Nylon | 17 | 165.9 | 93.4 | Japan |
Both the tensile strength and knot strength are exceptional and the graph shows that this string is very “elastic” which is a good thing for tennis racquet string but sometimes just not considered.
Head FXP 17
The area under the solid red lines is considered a stress-strain curve and indicates the “elasticity” of string by how close the lines fit from 0 to 50 three (3) times. A perfectly elastic material would be one line even though it went through three (3) cycles. What you see here is quite good and one of the reasons it is the winner!
Prince Vortex 300
The new Prince Vortex design is a new offering of an older string pattern with 14 main strings and 21 cross strings in a variable taper beam…whew! You can see by the throat design that the main strings are longer that a conventional throat design. The longer the main strings the more energy they can return…sort of, and in some cases!
Vortex 300
The beam starts at the grip with a strong 25mm then tapers into a 23mm at the throat and then back to 25mm at the tip. Do not let the beam dimensions fool you! The RDC flex of 59 after stringing is quite acceptable for most every player style.
We have been taking coefficient of friction (COF) data for years but have not included it this review format, until now. The 14×21 string pattern is unique enough that it is worth including. You will see the numbers on the review specs so we won’t go into them now, however the numbers are interesting.
The 14 main strings contribute to a very “open” area right about where most extreme “spin” shots are hit according to our data of string failure positions.
The frame geometry is sort of “Aero” like. The shaft is trapezoidal that transitions into a “reverse” trapezoid around the head. It makes the racquet look stiffer than it is!
Take a look at the specs then pick up a demo to see what the numbers mean to you!
| Manufacturer | Prince |
|---|---|
| Racquet Model | Prince Vortex 300 |
| Reference Tension | 56 lbs - 25.4kg |
| String | Victrex 7718 |
| Machine Used | True Tension Professional |
| ASPS, RDC | 45 |
| ASPS, FlexFour | 58.5 |
| Racquet Flex, RDC | 59 - After stringing |
| Racquet Flex, FlexFour | 40.0 |
| Racquet - In Plane Stiffness | 526.3 lbs/Inch |
| Weight, Grams | 322 |
| Weight, Ounces | 11.36 |
| Balance, mm | 320 |
| Balance, Inch | 12.60 |
| Length, Cm | 68.6 |
| Length, Inch | 27.008 |
| Head Width | 9.94 |
| Head Length | 12.94 |
| Head Area, cm2 | 652 |
| Head Area, Sq. Inch | 101.1 |
| Number of Main Strings | 14 |
| Number of Cross Strings | 21 |
| Ratio Cross/Mains | .512 |
| Main String Grid | 7.30 |
| Cross String Grid | 9.50 |
| Density (% of head filled with string) | .686 |
| Average Cross String Space | .452 |
| Average Main String Space | .521 |
| Dynamic Tension, Kp, ERT | 32 |
| Dynamic Tension, Lbs/in | 176.98 |
| First Moment, Nm | .790 |
| Polar Moment | 336 |
| Torsional Stability | 17 |
| Swing Weight, Kg/cm2 | 319 |
| Swing Weight, Ounces | 11.25 |
| Swing Weight Calculated | 329.7 |
| Power, RDC | 47 |
| Control, RDC | 52 |
| Manueverability, RDC | 74 |
| Power, Calculated | 1921.1 |
| Head Points | 7.24 |
| Head Weight, % | 46.6 |
| Center of Percussion | 21.7 |
| Dwell Time, ms | 9.48 |
| Efective Stiffness - lbs | 30.2 |
| K, Lb/In | 144.23 |
| Recoil Weight | 165.41 |
| Twist Weight | 237.56 |
| End Weight | 134.5 |
| Tip Weight | 189.0 |
| 9 O'Clock | 96.2 |
| 3 O'Clock | 96.1 |
| Butt Cap | 131.4 |
| Coefficient of Friction: M | .400 |
| Coefficient of Friction: X | .262 |
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