7 Factors That Affects Stringbed Stiffness

Part 1: Tension

"The strings feels hard/soft"

"I can't smash / hit hard enough"

"My shots are not going to the base"

The magical number that almost everyone playing racket sports or in the trade are talking about. On its own, it's a number that stringers input into their machine's known as "Reference Tension" measured in the form of kg or lbs, while some would think how hard that translates into onto a racket. The tension head then in turn pulls the string when activated creating the "Actual Tension" on a single string. Eventually all this forms a bed of strings on the frame. This bed of strings is notoriously known as "feel" or "tension" is actually known as Stringbed Stiffness (SBS) or "Dynamic Tension(DT)" measured in the form of kgf/cm2 or n/mm2, which affects the trajectory of the ball or shuttle. Racket frames are subjected to compression pressing from the sides and top during the QC checks known to many as "Recommended Tension" which might not be the actual stringing tension that the frame can hold. There are many forms of testing like bouncing a shuttle on the racket, frequency or harmonics test, using hand to hit on the racket string face or using smartphone apps to measure returning the measured values in the form of actual / reference tension. The stiffer the stringbed the harder it feels or vice versa. A little visualization is required, when you are holding a bow and arrow, if the bow strings are stiff and cannot pull towards your body, when the arrow shoots out, it goes short and fast. Sounds familiar? Or when the bow strings are soft and able to pull towards your body, when the arrow shoots out, it goes far and slow. Dynamic Tension in short affects the throw or placement known as trajectory, when formed up on the racket and when using the same force to hit:

  • The harder stringbed would give you a better placement but shorter throw.
  • The softer stringbed would give you a further throw but compromising the placement.

Unlike archery, badminton or tennis is an impact sports, the shuttle/ball is not thrown while stationary on the racket face but thrown when in contact with the stringbed. Thus the harder you hit, the longer the dwell time on the racket. Therefore when you hit hard onto a soft stringbed, the dwell time is longer causing the shuttle/ball to stay longer on the stringbed before it gets thrown out, resulting to a short and slow throw. Adding tension on the crosses? When you add or subtract tension aka pulling force on the crosses/mains or having incremental increase/decrease, it is to prevent/create racket deformation. Some players like to have their rackets stay as close to the original shape before stringing while some like to have their rackets slim and long, claiming that it will add the few millimeters to have a higher contact point or longer reach. Ultimately, the golden rule is that the racket retains its shape before and after stringing. Legit? All racket frames do deform, it's just a matter of how much, whether the naked eye can see or detect, while some would use a pair of digital vernier caliper to measure. Then how does tension affect the stringbed stiffness? When combined with the 6 other factors:

  • Frame size
  • Open / Dense String Pattern
  • String diameter
  • String material
  • Stringer skill and techniques
  • Stringing machine

The more variables used each time a player restrings their racket with, then there would be more permutations or combinations of the end result (SBS) which results to a different "feel" each time.

Part 2 & 3: Frame Size & Number of Holes on Racket frame

Racket frames comes in a variety of sizes, the bigger the frame, the longer the length of string is used thus creating a softer SBS and vice versa. The number of holes on the racket can range from 72 to 96 holes on a badminton racket. Technically, the more holes or the mains and crosses that a racket have would create a denser stringbed resulting to a higher SBS/DT. Let's take 2 identical badminton frame sizes as an example, a 96 hole racket frame would have a denser stringbed when compared to a 72 hole racket frame. Thus different brand manufacturers would create varying combinations or permutations depending on the racket frame design and structure.

Part 4 & 5: String Diameter and Material/Built

String diameter affects the hardness and softness of the stringbed, technically a thicker string would feel softer while a thinner string should feel harder, sometimes its just the other way around, as manufacturers tries to create different "feels". Not forgetting that a thick string would also result to a denser stringbed than a thin string. Material/Built properties of a string reflects on how much R&D a manufacturer put into a string and again it affects the hardness/softness of the string itself creating more permutations when matched with the racket frame and tension.

Part 6: Stringer Skills and techniques

Stringers would adopt different stringing patterns recommended by manufacturers based on their preference. The main difference between stringing patterns used is the overall length of string used to string a racket. Based on the same frame using 2 different stringing patterns, the pattern that uses a longer length of string would result to a softer string bed, while 2 different size frames with the same pattern and tension would result to 2 different SBS.

Part 7: Stringing Machine

Not all stringing machines are perfect, stringers/shop owners buy stringing machines based on their budget and preferences. Machines are divided in 2 main categories "Constant pull" and "Lock-out" differs by the way the actual tension is applied to the strings, while the clamping system dictates the way rackets are strung. Many moons ago, where top down stringing for the crosses is the norm, then was changed to bottom up, subsequently added 2 pounds on the crosses and now the extra tension on the crosses is removed. The change is due to machine technology improvements thus the stringing techniques or patterns are changed to match the machines characteristics instead of being a MUST.

Other factors:

There are secondary factors that could affect stringbed stiffness which includes climate, humidity and sea-level. All the factors are intertwined/ linked to each other thus creating varying permutations with even more variations when switching to different stringer’s each time you string with a combo of changing the constant values. To conclude, tension required/requested is overall an input value, how this value is represented depends on which side of the machine we stand, shall we embrace that the other 6 factors exists or to neglect it thinking that tension is everything. Discuss with your stringer and get the most appropriate approach to your needs on the court.



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