Category Archives: Kinesiology
SBS…what is it and why should we care?
We have made several posts regarding SBS, which is “String Bed Stiffness” and this is another one!
If you read this post we really need your comment(s), really!
String bed stiffness is the “feeling” when the ball hits the string on a tennis racquet. Due to the various string materials there will be “soft” and “hard” feelings. But wait, there’s more!
The string bed is made up of several strings, some longer called the Main string (M)and some shorter called the Cross string(X). Using “reference” tension each of the sets of string will be pulled at the same machine setting! It the machine is set at 50 pounds the tension head will stop pulling when it feels 50 pounds of resistance, regardless of what he tension inside the racquet head may be.
Let’s say you come into the world headquarters and we ask you what SBS you would like to have? Would you know? Probably not and not many would! We have grown up using the term “reference tension”, not SBS.
Reference tension is “number” you would ask your racquet technician to set the stringing machine tension system on. That number will probably be between 30 and 60 pounds (≈13 to 26 Kilo).
So, depending on many other variables, such as string material, string pattern, stringing machine, stringer technique, etc., you can end up with may different versions of the same “reference tension”.
A better way, and one we have been using for over thirty (30) years, is SBS but not everyone has bought into the concept, even though a qualified racquet technician will have a way to measure SBS! Maybe because it is too much trouble to figure out what your desired SBS from machine X would be from machine A! It is not!
There have been several really good SBS data collection devices but they have been difficult to use, and pricy! Not to mention gigantic!
Would you purchase a SBS data collection device?
How much would you pay for such a device?
Would you prefer a mechanical device or an electronic device?
The device must be portable, that is easily carried in a racquet bag or backpack
Yes or It doesn’t matter
It must be easy to use.
If you use an SBS device would you use a racquet technician that did not know what SBS is or how to measure it?
Thank you for adding your comments to this discussion! It is important stuff!
Head Lynx Touch! Two for One?
Several weeks ago we received the first sets of Head Lynx Touch 17 gauge strings. Yesterday we received the Lynx Touch 16 gauge version and want to share the differences…numerically!
Quickly, this string is composed of two (2) separate but “combined” filaments. So, is this a monofilament or a multifilament? The numbers indicate it reacts like a monofilament as we have become familiar with it.
Let’s start with the 17 gauge version:
The area under the heavy red lines is the “stress/strain” curve and we see that this string takes 23.5mm to reach the 50-pound mark. This is just a number unless it is compared to other strings so it is neither good nor bad, right now!
You can see that the string will hold up to 149.8 pounds before it breaks. This is tensile strength and may be important when considering the amount of “notching” that can occur. The “knot” strength of this version is 132.4 pounds.
Now let’s look at the 16 gauge version:
The difference is subtle. The 16 gauge version is a little stiffer (expected) and a little stronger in tension (also expected). The “knot” strength of this version is 133.6 pounds.
What is interesting is the “grouping” of the stress/strain cycles on both strings. They indicate a good elasticity. The closer to the “zero” point on unloading the better!
In our opinion, both versions of the string would be considered “stiff” and suitable for the player looking for a stiff but stable string as our creep test confirmed.
If you currently use stiff strings and would like better consistency this would definitely be a candidate ./
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.
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.
Head Prestige Tour 2021
This racquet has the potential to be the hottest new Prestige in a long time. The “Tour” series is not new to the Prestige line but this one has some differences that are meaningful, we think!
This new Tour is a 16×19 string pattern inserted into a 95 square inch hitting area! Compare that to the previous Tour with a 18×19 string pattern in a 99 square inch head(now the new Prestige MP)…so you can see where this one is headed!
Also included in the Prestige Tour is the Auxetic material and construction that is intended to provide a better feeling impact and maybe a little more “energy”. The shaft has a slightly different geometry and is a little shorter than some other models, however, the graphics indicate the shaft is “elongated”.
The “box” beam is a relatively constant 22mm from start to finish and is beautifully done in matt black transitioning into the Prestige maroon.
|Racquet Model||Head Prestige Tour 2021|
|Reference Tension||53 lbs - 24.0 kg|
|String||Victrex 7718 (PEEK)|
|Machine Used||True Tension Professional|
|Racquet Flex, RDC||63 - After stringing|
|Racquet Flex, FlexFour||42.5|
|Racquet - In Plane Stiffness||384.6 lbs/Inch|
|Head Area, cm2||608.9|
|Head Area, Sq. Inch||94.4|
|Number of Main Strings||16|
|Number of Cross Strings||19|
|Main String Grid||7.20|
|Cross String Grid||9.125|
|Density (% of head filled with string)||.695|
|Average Cross String Space||.464|
|Average Main String Space||.445
|Dynamic Tension, Kp, ERT||34|
|Dynamic Tension, Lbs/in||190.16|
|First Moment, Nm||.844|
|Swing Weight, Kg/cm2||331|
|Swing Weight, Ounces||11.68|
|Swing Weight Calculated||357.1|
|Head Weight, %||47.6%|
|Center of Percussion||21.1|
|Dwell Time, ms||9.00|
|Efective Stiffness - lbs||27.9|
And The Winner Is…
The winner is Tecnifibre MultiFeel 17!
This string, MultiFeel, is a very “soft” polyurethane bonded construction that offers playability and a good value!
This graph shows the high elongation and nice elasticity of this string. The fairly linear slope up to failure would indicate some consistency of shot all the way up to breakage!
The knot strength is pretty good for a thin multifilament and we can say from experience that the know is going to be fine when property “tightened” and large enough to not slip bak into the grommet barrel.
If you are considering a multifilament this would be a good one to try!