Japanilaista tuotemerkkiä Kumpoota Suomessa edustaa Qiu Weijie, eli Stone. Stone on myös koulutettu mailojen jänteyttäjä. Tässä hän kertoo näkemyksiään sulkapallomailoista ja niiden jännityksistä. Juttu on englanniksi.
How to Choose a Suitable Badminton Racket and What Makes It Important in Stringing
Based on statistics, there are about 30 kinds of most common ball sports, among which 11 are in Olympic Games. It is seldom that people know badminton consumes huge energy comparable to top competition of soccer, basketball and volleyball. The average time of a badminton match is about half of a tennis match, however, the running distance and the number of racket waving are almost double. Considering the size of a tennis court is about double size than a badminton court, badminton player runs much more forwards and backwards. Compare to an NBA matches, which scores over 100, the average running distance of a player is about 3500 meter. However, the average running distance of a professional badminton match is easily over 7000 meter. The fastest smash of badminton is 343km/h while 225km/h in tennis. Playing double is even more demanding than single. The average number of racket waving is 15 times within 20 seconds. In a match of 45 minutes, there will be over 1000 times racket waving per player. About 50% of those waves are smashes, which average speed could be 289km/h. Players need to make over 300 times body turn over 90 degrees in a match.
It is a dream of every player to have a best racket of their own, which helps to reach fastest speed, biggest power, maximize techniques, best mistake tolerances and super durability, in playing such one of the most demanding sports. For a normal badminton enthusiast, it is even more difficult to select a good racket from thousands of new models every year.
Some essential factors of a badminton rackets are to be mentioned in this article. It is important to find a racket with most suitability rather than prices. More expensive does not necessarily equal to excellence depends on cases.
Physical weight vs. Swing weight
The weight of a racket is normally marked on the shaft with unit ‘gram’. The number shows the physical weight with empty frame without grip and any other additives. It is also marked in another international format ‘U’: U: 95-100g; 2U: 90-94g; 3U: 85-89g; 4U: 80-84g; 5U: 75-79g. Suppose all other variables remain same, the more weight, the more power player will get. In another words, it is easier to hit shuttlecocks far with heavier rackets in condition of all other factors are same.
Many players already have an opinion of the weight they are used to when selecting a racket. However, some of them are not satisfied with the new racket, even they purchased the one with exactly same weight as previous model. It might feel ‘not as light/heavy as the weight says’ when playing. This is because of neglecting how the weights are distributed in the racket. The factors of physical weight, racket length and racket balance are described as ‘swing weight’ in the terminology of racquet sports.
Swing weight is a factor which could be measured by a swinging device holding the racket from 4 inches of the bottom and swing. The measuring results read in a unit of ‘kg m2’. The normal range of a badminton racket is from 80-100kg m2. Swing weight decides how fast player could swing, which interprets ‘feeling light or heavy’. Conditioned by the same swing speed, the more swing weight, the more power player will have. Swing weight can also be measured and estimated by an APP called ‘swing tool’.
The balance of a racket is measured by a balance board. It is presented in unit ‘mm’, which describes the distance between buttom and the balance point of a racket.
- Normal range: 280-300mm
- Head heavy: >288mm
- Head light: <288mm
The length of a badminton racket measures from bottom to top of a racket. The length of a modern racket is 675mm. 680mm is the longest length which BWF regulates a badminton racket. There is measurement tells that 5% more racket length will increase 30% more hitting area. See the effects of length to a racket as follow:
- Normal range: 664-680mm
- A standard length of a badminton racket: 664mm
- A long badminton racket: 675mm
- Offensive: 675-680mm
- Defensive: 665-670mm
Stiffness of Shaft vs. Frame
Stiffness of a shaft is measured by a machine jig which keeps distance of 23cm between two fixing point of a shaft. Weight of 20kg is slowly added to the middle of the fixed part until stand still. The vertical deformation of the shaft is measured to describe how stiff the shaft is in millimeters. The bigger the stiffness, the more flexible the shaft is. There are different descriptions of stiffness in different brands. Some of them tell exactly the number, while some just tell hard, moderate soft or 1, 2, 3, 4, 5. It is always good to ask the dealer the exact stiffness of the shaft before purchasing in order to compare with difference rackets among different brands. Most common stiffness could be found in the market are as follow:
- Stiffness: 8.0: hard
- 8.5: moderate hard
- 9.0: moderate
- 9.5: moderate soft
Offensive and powerful playing style ranged stiffness between 8.0 to 9.0mm; defensive and flexible playing style ranged from 9.0 to 9.5mm in most cases. The more flexible the shaft, the more momentum it can bring to the shuttlecocks, which turns in the form of power smashes for instance. Conditioned by same hitting power, the softer the shaft, the more possibility to bend, the more bending distance, the more hitting power, the less shock, the longer time shaft need to recover, the worse the angle control, which is not good for continuous smash and small drop close to the net.
The shaft of a badminton racket is the secret ingredient to make such high flying speed of a feather shuttlecocks compare to other racquet sports. Thanks to the modern technology that a lot of creative ideas could be realized in this critical factor.
Looking back ten to fifteen years, the technology of materials is far behind the current ones. The biggest sign is that the material of a racket is much heavier and softer than the one we see now. Therefore, manufacturers have to make shafts more stiff to bring clear shots for professional players. It is still the same principle now, however, not the only solution.
In tradition design, the only way to have more power in attacking is make head heavy. Nowadays, it is possible to control the bending point of a shaft in high, middle or low position to emphasis the characteristics of a player. It is also possible to find a racket with different stiffness in different sides of a shaft so that player gets forehand shots more power and backhand shots easier control. Good technology is not only designed for professionals, but for every player an easier and more pleasant game as well.
Since the duration of a shuttlecock stays on rackets when smashing is 0.004-0.006 second, it is a must to make a very stiff frame so that it recovers as fast as possible right after every hit. For the shaft, it is time to change a bit the traditional mind set for the reason of new technology. It does not have to be correct any more that the professionals only use very stiff shafts.
Shapes of Frames
There are three shapes of racket frames in the market, as follow:
- Traditional: 330 cm2 (51 in2)
- ISO: 340 cm2 (53 in2)
- Extra-ISO: 370 cm2 (57 in2)
The direct influence of racket frame is to sweet spots. Sweet spots are also known as effective area that could apply to a flying shuttlecocks. The bigger the sweet point, the bigger the power, the less the control and accuracy.
Due to zero tolerance to a mistake in a match, most professional players started to use Extra-ISO frames. It can help more to a normal player even if sometimes the hits are not so accurate. The traditional frames are rapidly replaced by ISO or Extra-ISO ones.
Cross Section of Racket Frame
An ideal racket should have good flexibility and speed when waving and a lot of power when smashing. It
sounds greedy, however, not difficult with the help of modern technology of manufacturing. It can be realized by difference cross section applying to different parts of the frame. Besides the speed and power, it can also bring durability, stability and so forth to the same racket. The most common cross section of a frame could be found below:
- Box-shape: strong support, good share resistance, bad swing flexibility
- Wing-shape: good swing flexibility bad control, etc.
It is common to use box-shape on the throat of the racket and blade design on wing sides of the frame. The idea is to make it very stable and durable in the connection between frame and shaft and blade design could minimize the wind resistance to get a ‘light feel’.
There are rackets with three or more different cross sections applied to same frame to reach different ideas of designers. It will come more and more new options of cross sections of a frame as the time goes by and it is wise to select the suitable ones which helps the weak points of playing.
Handle and Grip Sizes
In Europe, the most common handle sizes are G4, while it is G5 in Asia. There is always a need to have some space in between middle finger and hand after gently hold the racket. Too small handle can cause throwing racket away during play and not enough smashing power, while too big handle can cause injuries of muscles from hands and arms. Using different grips could easily enlarge the handle sizes. Many professionals use heat shrinkable tube to resize the handle, in which way much smoother and keep the sharpness of the feeling of wood edges.
It is important to pay attention to the way of putting new grips, especially thick ones. The correct way can bring best playing comfort. Left handed player should use left hand to tight the grip and use right hand to hold the racket, as shown in below right picture. And vice versa to right handed players, see below left picture.
String Bed Density and Pattern
Every badminton brand has its own philosophy of designing. There is not a saying which one is clearly better than others. The obvious what we could see is the number of holes in a racket frame and what types of grommets they use. The number of holes differs from 72 to 96. The higher density, the smaller tension is needed to generate same power. For instance, a racket with 96 holes can lower the stringing tension by 30% to get same string bed stiffness as the one with 72 holes, conditioned by all other factors remain same. The less mains and crosses, the easier to spin the shuttlecocks, however, less stable. The higher density brings more stable hits, however easier to get frame broken and more stringing works. It is because of the strength of the frame is lower when having more holes.
There are about 55 different grommets in the market of different lengths, shapes, materials, colors and so forth. Good grommets protect frame not hurt by strings and not cut the strings by its sharp edge. Some good grommets also mistake prevent of string crosses from outside the frame. If grommets cannot make one of above mentioned functions, it is time to change new ones. It does not necessary have to use the exact same grommet during change, however, the principle is to keep the design idea of the racket as much as possible.
The materials of the rackets have huge variety in the market. Besides the most common high modulus graphite, it is also interesting to see how it compare the stiffness, strength and shock absorption with traditional ones. It is recommended to start with a 100% carbon graphite racket even with a starter or junior. There is aluminum alloyed rackets on sale in the market. It is good to arouse some attention when the price of the racket is low. The simplest way to identify between graphite and aluminum alloy is to feel with bare hands. The aluminum alloy feels clearly colder than graphite. Moreover, most popular materials such as titanium, woven, Kevlar, basalt will be introduced below.
Titanium has the feature of high restorability and anti-torsion. It contributes to a lightness as a feather appeal with the strength of a bull. Not only are they durable, they actually can improve swinging.
According to SOTX, ”Woven Material is made from a combination of 800D high grade carbon fiber and high grade glass fiber. It produces a racket with far greater elasticity than from the traditional material, resulting in far better grip. Woven is through a process of high technology. It does not contain liquid form material. The racket is therefore more stable and more efficient in impact control.’
Kevlar is a material used mostly in armor materials such as bullet proof vest, for its excellent performance of light weight, strength and flexibility.
Basalt is a natural volcanic rock, which can be used in manufacturing where it is made into fine gold fibers with incredible vibration resistance. The basalt frame brings smooth feel of playing.
Muscle Injury and Tennis Elbow
Injury is an enemy to all kinds of sports. The most common injury of badminton is from muscle and tennis/badminton elbow. The cause of such injury is from wrong way of using fingers and twists. The second big possibility is not hitting the sweet spots of the frame. There are many good suggestions depending on different cases. During the selection of a racket, the injury must be considered to be an important factor.
It is recommended to use more stable rackets. Rumor tells to use lighter rackets, which does not have a scientific clue to follow. The reason of muscle injury is not mainly because of the weight of some grams. By contrary, it is because of the shock during hitting. Wrong hitting position and missing sweet spot causes even a lot more shocks than usual. The good suggestions are as follow:
- Check the handle size and tune it to proper thickness
- Adjust the hitting position and aim at sweet spots
- Use thin and soft grips
- Lower string bed tensions
- Use soft and thin strings
- Add some weight to wing sides of the frame to minimize the shocks
- Use racket with good shock absorption such as Vectran fiber
A racket with smart function which can record the power, speed and angle of every hit. It summaries all the technical data after every training and matches. It compares the difference between your data with those professionals and tell what to improve. It is possible to see if the training amount is enough by measuring how many calories burnt and share all these with your friends and coaches.
It is not a future story in the movie. There is already been this kind of smart racket lately released. Grab one and this is the future.
High Quality Stringing Works vs. Speed
The three principles of good stringing works are ‘maintain the original shape of the racket’, ‘minimize the harm to strings and rackets’, ‘consistent results of string bed stiffness’. No matter when the stringing works happen and who is the stringer, it is always important to follow the principles. The discussion is about in what priority sequence. Please note that the speed is not on the top three list. Many people evaluate if a stringer is good or not by asking how fast he or she could string a racket. There are huge varieties influence the speed of stringing works, therefore it is suggested to take a first look at what we mean quality stringing works. Talking about speed without quality is meaningless.
Maintain the Original Shape of the Racket
This is a rather understandable principle of keeping the shape of the frame exactly same before and after stringing. Modern stringing machines have six or more fixing jigs, which is considered to be enough to secure the shape of racket of no deformation. In fact, it is not totally true. No matter six or even eight fixing points, the deformation happens anyway. It is only a matter of how big it is. It is acceptable if compare an empty frame with a strung racket, which lengths are looking same by our bare eyes.
To achieve this principle, it requires a stringer to start and finish the stringing work at once. Some stringer goes for coffee or lunch with the stringing work half done. There is a big risk of obvious deformation especially of high tension and the number of finished mains and crosses are strongly uneven. A simple experiment was made to leave the racket with only mains strung tension of 12kg in a best stringing machine in the market. The frame looked ‘round’ after half an hour.
There are also some tricks to help realize this principle: add extra tension in crosses. Due to the mains and crosses are not possible to be finished at same time, crosses need a bit more tension to pull back the deformed frame and against the resistance mains apply to every cross. Some stringers add 1lb to those strings far away from sweet spots and 2lb to those crosses in sweet spots. Since it is difficult to know exactly where the sweet spots are for so many variables and the influence of those crosses far away from sweet spots doing minor influence, United States Racquet Stringer Association and China Racquet Stringer Association recommend to add 2lb to all crosses.
Minimize the Harm to Strings and Rackets
Due to the friction in between mains and crosses during stringing, the violent pulling could burn the surface of a string, which causes the string much easier to break. It is recommended to repeat the process of losing the crosses and pull to minimize the harm to strings.
It is also common to see the surface of the string is broken or scratched by sharp stringing tools when getting through anti-double grommets, or slippers inside the clamps. Slips inside clamps is no good, however, too tight clamp can also cause the deformation of a string. It requires a stringer to adjust several times the tightness of clamps during one stringing work.
Consistent Results of String Bed Stiffness
Most of players go for a re-stringing work by telling a tension of some kg. It is not wrong, however, a lot to know before it is right. The number of kg is set in the stringing machine. There are so many different models of stringing machines in the market, of which totally different accuracy. It is important to point out that most of old electronic stringing machines pull too tight rather than too lose. Suppose all other factors are same, players seldom get exactly same string bed stiffness with two uncalibrated machines. How about thinking ‘materials of strings’, ‘diameter of strings’, ‘number of mains and crosses’, ‘location and type of grommets’, ‘stringing patterns’, ‘techniques of stringers’, ‘angle between every pull and rackets’ are all variables can directly influence the results. Do we still think it is enough to describe string bed stiffness with a fixed number of kilograms? A racket of 96 holes strung with thin and hard feeling string could be about 30% more stiffer compare with a racket of 72 holes strung with thick and soft feeling string under same accurate pull of 12kg.
The good way to describe string bed stiffness is ‘Dynamic Tension’, which tells how big force it is needed to press the string bed 1mm down during play. It is a very good measure since it is exactly what players care during the play, rather than what number is set in the stringing machine. Dynamic Tension could be measured by several ways. A professional stringer will measure every racket he or she strung and make sure the measure of Dynamic Tension is within minimum tolerance. It is also the responsibility of stringer to remind customers to adjust the pulling tension in different cases.
Daily Stringing vs. Tournament Stringing
Since the demand of stringing works in tournaments are severe, ‘speed’ is considered to be important. It requires to string averagely 25-30 rackets for a stringer within one day. If the sequence of importance to follow in tournaments is 1. Quality 2. Speed 3. No harm to rackets. It should be another way round in daily stringing works 1. No harm to rackets 2. Quality 3. Speed.
The ‘tournaments’ mentioned above are meant for those international ones, of which most players get equipment sponsored. Therefore, they care more about the quality of stringing work and how soon they could get their rackets ready. Stringer will treat a little differently when cutting the old strings and string the new ones. However, a normal customer pays a lot of money for a good racket and a good stringer should place ‘no harm to rackets’ on the top priority. Some ‘harm’ are not seen immediately, while shows in a long run.
Authorities to Follow
There are three top Racquet Stringer Association around the world to follow and they provide the latest knowledge of stringing.
- United States Racquet Stringer Association (USRSA)
- China Racquet Stringer Association (CRSA)
- European Racquet Stringer Association (ERSA)
Where to Learn More
More interesting topics such as ‘modern technologies of badminton equipment’, ‘the relationship between factors and string bed stiffness’, ‘how to fine tune a racket so that different rackets could feel the same’, ‘what makes professional stringing work for different brands’, ‘how to resize the handle’, ‘what are the difference between strings and so forth’. Contact email@example.com
Introduction of Author
Stone Qiu Weijie, CEO of Badminton Quality, the importer of Kumpoo, the second biggest Japanese badminton brand in Nordic countries. Currently the exclusive badminton shuttlecocks and clothing sponsor and supplier of all level Finnish National teams. Certified Stringer in both CRSA and USRSA.