Category Archives: Evaluation
Power vs String Bed Stiffness
We have been testing strings for power potential since 1984! Currently, we have over 500 strings registered on our website, and we will put a link in this post that will take you there. Over the years, we have tested that several times that number but need to remove some strings that simply do not need to be in this data while keeping “legacy” strings for reference to today’s offerings.
What does the power potential of string have to do with String Bed stiffness? While a single strand of string tells us a lot about the performance characteristics of any string, it is the total string bed that you play with, not a single string!
We test for String Bed Stiffness in four (4) different ways: Babolat RDC, Flex Four, Master Tensometer, and our proprietary String Bed Master.
What we want to clarify is the power of the string bed stiffness, and to do that, we need to include the tennis ball, which is, by design, not very efficient. I believe the rebound percentage is about 53 to 58 percent. If the rebound percentage were closer to 100 percent, the ball would not stay in the court!
The graph below helps us understand what String Bed Stiffness will work in any given player situation.
Power vs String Bed Stiffness
I know there are a lot of lines, but I am certain you can understand them. We will help you along and explain why this is very important to you and us!
The vertical axis (Y) is Power, and the horizontal axis (X) is String Bed stiffness in pounds per inch. Every device we use for string bed stiffness presents the force in pounds per inch. The green dotted box represents the “normal” range (≈ 160. to 210.0) for string bed stiffness.
If we want to maximize the power of the ball contact and string, we would need a string bed stiffness of about 100 pounds per inch, which is achievable but not “normal.
The upper curve (brown or red) represents the sting bed only. So you see a power range of 20.0 down to 6.67. The lower curve (blue) introduces the ball and, due to the ball design, does not add any power but detracts from power. So you see a power range of 13.7 down to 8.38. Because we don’t know how hard the ball is being struck, we prefer to use the string bed-only curve. It is, however, critical for us to know how the ball is participating.
An interesting and important value of the graph is the power value. As the string bed becomes stiffer than the ball (≈ 210.0 pounds per inch range), the ball will provide more power than the string bed. Not much, but at least the ball will not detract from the power!
Another 1000 Word Picture!
What happens to a string if it gets scuffed or slightly damaged in terms of properties?
We know the string will not go in the clients’ racquet, but how bad is it, really?
The chart below shows exactly what happens to each string until both fail. We can see precisely how the scuffing affects the string. Both strings behave nearly the same through the three (3) cycles to 50 pounds. We then see that the scuffed string gives up a little earlier than the clean string by about 15%.
So, what’s the Difference?
However, the failure force for both of these strings is very high! Only a handful of strings we have tested exhibit this tensile strength.
So we know this string would never be used in a client racquet, but you could certainly use it for some “experimentation!” And, of course, depending on how many and where the “rough” spots are you can cut that portion away!
A Picture is Worth a 1000 Words?
Yesterday @ the World Headquarters was full of interesting stringing! So we decided to do some testing of some of the strings that were just waiting to be broken!
The chosen strings are Ashaway MonoGut ZX Pro 17, Tecnifibre Triax 17, and Volkl V-Star 18—three totally different materials. Our purpose is to determine a string’s properties before it goes into a tennis racquet. Our testing quantifies these properties, and then the “feel” component comes from the player.
A 1000 Words?
We normally do not do more than two (2) overlays because it is a little messy, but these strings begged to be compared, so here it is!
Our Questron can cycle automatically, so the stop points are pretty precise. All strings are cycled from two (2) pounds to fifty (50) pounds and then until they fail or ultimate tensile strength (UTS).
In the Displacement axis (X), the shorter the distance in mm to 50 ponds, the stiffer the string. The straighter the line is to fail, the more consistent the feeling until failure.
The testing confirms that Tecnifibre Triax does contain some stiffer fibers. The other strings are monofilaments, so there are no fibers.
Racquet Quest uses a bunch of each of these strings for obvious reasons and, of course, depending on the player.
Monofilament Material Comparison
Most monofilament tennis strings are polyester, a blend of polyester, or PEEK.
As you know, we believe there is no wrong string, just wrong applications. The graph will show the comparative stiffness of three (3) materials. The string is pulled at a rate of 1mm per second. The resultant spreadsheet for this particular test is about 5300 rows long.
With our spreadsheet, we have access to every mm of data. Maybe sometime we can post some of the individual data points.
Blast is polyester, V-Star is a unique blend of material (I do not know what it is), and MonogutZX is PEEK (polyetheretherketone).
The graph shows the cycle from 0 to 50 pounds three (3) times, then to failure (UTS). The quicker (shorter distance) the string reaches the 50-pound mark, the stiffer it is. MonoGut ZX did not fail in the 180mm excursion. You can see, in this case, the stiffer string fails at a higher force but shorter excursion.
Stiffer strings deliver less power and have a higher shock value. The midrange stiffness shows exactly what would be expected, and the softest string also indicates expected results.
Racquet Quest, LLC
