In this blog, for understanding a blade and comparing blades, four performance indices – two elasticity indices and two vibration indices – will be used.
- Ep : Elasticity Index (Primary)
- Ec : Elasticity Index (Central)
- Vp : Vibration Index (Primary)
- Vl : Vibration Index (Lateral)
As the name itself expresses elasticity index means the elasticity (= stiffness) of blade. So it is directly concerned with speed of blade. Especially Ep is similar to speed. Ec becomes meaningful only when we hit blade very hard. The higher value of Ec means that the blade can give more ‘kick’ when we hit the blade very hard.
Vibration index means the level of vibration. Vp is directly concerned with longitudinal bending vibration, and it is mainly transferred to player’s palm. Vl is concerned with lateral vibration of blade head, and player can feel it at fingertip of index finger. So Vp and Vl can be translated as ‘feeling’. The higher value of Vp or Vl means sharper feeling.
In this article, I will show the values for some known blades for the understanding on performance indices. I selected 10 blades as follows:
(1) 5-ply wood blades
- Stiga Allround Classic (Reference blade)
- Butterfly Korbel
- Tibhar IV-S
- Butterfly Mazunov
(2) 7-ply wood blades
- Butterfly Primo Powerfeeling
- Donic Ovcharov Senso V1
- Stiga Clipper CR
(3) Fiber blades (usually Carbon fiber)
- Yasaka Ma Lin Carbon
- Butterfly Timo Boll Spirit (same as Timo Boll ALC)
- Tibhar Rapid Carbon
- Butterfly Schlager
As you see above, there are three ‘groups’ of blades in this comparison. I tried to show you as various blades as possible. So I selected three kinds of different groups, and even I selected blades with various characteristics even in the same group. The reference blade is Stiga Allround Classic, and all the performance indices of Stiga Allround Classic are 1.00.
At first, let’s see Fig.01 – the comparison graph of Elasticity Indices. (Please note that ‘elasticity’ doesn’t mean ‘flexibility’ but ‘stiffness’ although the word itself can be translated both of those two. Throughout this blog, higher elasticity means higher rebound, i.e. higher speed.)
Red bars indicate Ep = ‘Primary’ Elasticity Indices. ‘Primary’ means bending deflection which is the most important behavior of blade during the impact between racket and ball.
Green bars indicate Ec = ‘Central’ Elasticity Indices. ‘Central’ means the deflection of the center of blade head, and Ec is the stiffness of that deflection. Before normalization, the value of Ec is much bigger than that of Ep. I.e. central stiffness is much higher than primary (bending) stiffness. So the amount of central deflection is smaller than primary deflection (= bending deflection).
Although Ec isn’t the value that doesn’t directly express feeling, the relationship between Ec and Ep can express a kind of feeling. Please also refer to Fig.02 when the relationship between Ep and Ec is considered.
If Ec is relatively bigger than Ep, player feels that the blade is hard at center of head because the relative ‘kick’ when we hit ball very hard is noticeably big. If Ec is relatively smaller than Ep, player feels that the blade is soft at center of head because the blade doesn’t provide additional kick when we hit the ball hard. Instead player feel that the blade head holds the ball. (In fact, usually the blade with high value of Ep also has quite high value of Ec. But, if Ec is relatively small, player can’t feel the additional kick by high Ec because basic rebound by bending stiffness is already very high. That is another reason why the behavior of blade center can’t be ‘primary’ when we examine the performance of blade.) Interestingly, if Ec and Ep are similar with each other, the behavior of that blade is linear. ‘Linear’ means that player doesn’t feel the additional kicking or holding. That is not an intended result of this research but just accidental after the use of poly ball. In the age of celluloid ball, to become linear the Ec should be relatively smaller. However from the introduction of poly ball, all of blades became softer at center of head. (It is another theme of research. But, I will not touch the detail of that phenomenon.)
From the graph, we can see that Butterfly Korbal has 54% bigger Ep (red bar) than Stiga Allround Classic. So Butterfly Korbel is faster offensive 5-ply wood blade while Stiga Allround Classic is slower allround 5-ply wood blade. But, the Ec (green bar) of Korbel is only 27% bigger than that of Allround Classic, and it is significantly smaller than the Ep of Korbel. So we can expect that Butterfly Korbal holds ball deep when we hit ball hard. Differently speaking Butterfly Korbel doesn’t give additional kick so much when compared with its basic speed that can be expected from Ep. In fact, we feel more additional kick from Stiga Allround Classic than from Butterfly Korbel when we hit ball hard although Stiga Allround Classic is apparently slower. That is because of the relationship between Ep and Ec.
Tibhar IV-S and Butterfly Mazunov are known as very fast 5-ply wood blades. It is proved by the values on the graph. Ep of Tibhar IV-S is 1.85 and that of Butterfly Mazunov is 2.34. Those values are close to the Ep of Stiga Clipper CR which is a very fast 7-ply wood blade or that of Butterfly Timo Boll Spirit which is a famous fiber blade. Also, we can see that Ep of Butterfly Primo Powerfeeling which is a 7-ply wood blade is smaller than that of Butterfly Korbel which is a 5-ply wood blade. Again, we can see that the Ep of Yasaka Ma Lin Carbon which is a carbon blade is smaller than that of Butterfly Korbel which is a 5-ply wood blade.
We may think that 5-ply blade is relatively slow and 7-ply or Carbon blade is relatively fast. However, that is not always truth. In the world of table tennis blade, there are many ‘relatively fast’ 5-ply blades and many ‘relatively slow’ Carbon blades. Of course there also exists actually fast carbon blades such as Tibhar Rapid Carbon and Butterfly Schlager on the graph.
From the graph, we can expect the characteristics of blades. For example, Butterfly Timo Boll Spirit is as fast as usual 7-ply wood blades but it tends to significantly hold ball when we hit the ball very hard. It doesn’t provide additional kick. Donic Ovcharov Senso V1 has similar characteristics with Butterfly Timo Boll Spirit. Yasaka Ma Lin Carbon is not a fast blade although it is a carbon blade. Its speed is similar to that of usual 5-ply blade or slower. But, its Ec (1.26) is close to Ep (1.38), and as a result its behavior is close to linear. (It tends to hold ball, but just a bit.) Similarly, Tibhar IV-S and Butterfly Schlager are close to linear.
By the way, although I mentioned that player can ‘feel’ the relationship between Ec and Ep, it isn’t the feeling that is directly felt by human hand. Both of Ec and Ep are performance factors, and the feeling of the relationship between Ec and Ep is not felt by hand but felt by brain. I.e. it is not ‘feeling’ but what the player judge or understand in brain while playing with that blade. What are actually concerned with feeling are Vibration Indices.
Then let’s see Vibration Indices. Fig.03 is the graph of the comparison by Vibration indices.
Navy bars indicate Vp = ‘Primary’ Vibration Indices. Again, ‘primary’ is concerned with bending deflection which is the most important behavior of blade during the impact between racket and ball. It is normalized value of the frequency of vibration. It is concerned with stiffness (= elasticity), but isn’t the stiffness itself. The primary (= bending) vibration is generally felt by player’s palm which is in contact with the handle of blade. More correctly speaking, the sensing point of Vp is little (fifth) finger and a part of palm which is close to little finger in case of shakehand. (In case of penholder, Vp is felt at the point between thumb and index finger.)
Orange bars indicate Vl = ‘lateral’ Vibration Indices. It is concerned with the vibration which is similar to the movement of bird’s wing. Also it is felt at the fingertip of index finger which is in contact with the wing of a blade. Sometimes Vl is more important than Vp because index finger is generally more sensitive than palm or little finger.
There is again the issue of the relationship between Vp and Vl. That is because those two are felt at different points of hand but at the same time. That may be more important than the single values themselves. Please also refer to Fig.4 when the relationship between Vp and Vl is considered.
The comparison between Butterfly Korbel and Buttefly Primo Powerfeeling gives us very good example. The Vp of both of those blades is 1.07. However Vl of Butterfly Korbel is 1.27, and is much bigger than Vp. And, Vl of Butterfly Primo Powerfeeling is 0.82, and is much smaller than Vp. Even though those two blades have the same value of Vp, we will expect that the feeling at the fingertip of index finger will not be same. Actually, Butterfly Korbel gives very sharp feeling at the fingertip of index finger, and on the contrary Butterfly Primo Powerfeeling gives very comfortable feeling at the fingertip of index finger. By the way, we may feel that Primo Powerfeeling is harder than Korbel. If a player says that Primo Powerfeeling is harder than Korbel, we can understand that the player mainly feels at the fingertip of index finger and then judge the feeling at the palm. This kind of complexity causes the inconsistency of the result of testing by human testers. A tester mainly feels Vp, but another tester mainly feels Vl. A tester judges Vl after Vp, but another tester judges Vp after Vl. We usually read many different opinions about the same blade on table tennis magazines or internet home pages. The reason why there can exist so many different opinions on identical blade is the existence of many factors of feeling. Human tends to biased to a specific element of feeling, and it affects not only the result on feeling but also even the result on performance. That is the reason why we can’t believe the result of subjective testing by human tester, even though that tester is a top player. However, the Vibration Indices – Vp and Vl – don’t give us biased result. We can believe the indices because those indices are ‘measured’ values.
Comparison between two 7-ply blades – Donic Ovcharov Senso V1 and Stiga Clipper CR is very interesting. On the palm, Stiga Clipper CR shows bigger value of Vp than Donic Ovcharov Senso V1. It means that Stiga Clipper CR is harder than Donic Ovcharov Senso V1 on the palm. So basically we can consider that Stiga Clipper CR is harder because bending deflection is primary behavior of blade. However, the Vl of Ovcharov Senso V1 is bigger than that of Clipper CR. It means that Ovcharov Senso V1 provides sharper feeling at the fingertip of index finger. So from the viewpoint of feeling, those two blades are totally different. We can understand that those two blade are designed under totally different concept.
Among four carbon blades on the graph, it is interesting to compare between Butterfly Timo Boll Spirit and Tibhar Rapid Carbon. Tibhar Rapid Carbon is thick and hard blade. But, Butterfly Timo Boll Spirit is thin and relatively soft blade. So the Vp of Rapid Carbon is high (= 1.70), and the Vp of Timo Boll Spirit is not high (= 1.26). However, at the fingertip of index finger, we may feel that those two blades are similar because the Vl of Rapid Carbon (= 1.52) is close to that of Timo Boll Spirit (= 1.41). Some players will say that Rapid Carbon is much harder than Timo Boll Spirit, but other players will say that Rapid Carbon is similar to Timo Boll Spirit.
I will skip the detailed comparison of Vibration Indices on the other blades because this article is for just showing the example of utilization of four performance indices.
As is explained above, by comparing the values of four performance indices we can understand table tennis blades without bias. So I will always use four indices in reviews on blades. I believe that it will help you to understand table tennis blades more objectively. Finally accumulated data of performance indices will help your fine adjustment when we want to select a blade which is the best fit for you.
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