The Long Pimple Guide

Lars Borg
What is a longpimpled rubber?
On the ITTF list of approved rubber sheets, long pimpled rubbers are categorized as those where the aspect ratio of the pimples is more than 0,9. Aspect ratio is the quotient between the length and the breadth of the pimples. If a rubber sheet has pimples with a length of 1,8mm and a breadth of 1,7mm the aspect ratio is 1,8/1,7 = 1,06. The aspect ratio is not allowed to be more than 1,1 if the rubber sheet shall be approved. This in effect means that very long and thin pimples not are permitted. Most long pimpled rubbers today have a pimples length between 1,5 and 1,8mm. In the ITTF list for approved rubber sheets 2006 there are 84 different long pimpled rubbers listed.
The playing characteristics of long pimpled topsheets
There are some main principles in the structure and placement of the pimples which gives the playing characteristics of a long pimpled rubber. With playing characteristics I mean such things as spin reversal, ability to produce wobbling balls, spin, reduce speed, create speed and control.
Spin reversal
Spinreversal is the ability not to influence the spin. If the longpimpled rubber recieve for example 10 units in topspin, a good antispin rubber change very little of the spin and gives back about 9,8 units in backspin. A longpimpled rubber with ribbed surface with some friction will instead change the spin a little and give back for example 8 in backspin. The longpimpled rubbers with the most pronounced spin reversal are quite hard and the pimples surface feel more “plastic” rather than as a rubber. As a result there is absolutely no grip on the ball.
Wobbling effect
A wobbling ball is a ball which moves in unpredictable way. The mechanism behind this seems not to be fully understood. Some explanations claims that it happens with balls without any spin at all, while other explanations say that it is a product of very strong non-pure spin for example topspin combined with sidespin. In practice it is the long pimpled rubbers which produce the wobbling effect and it is the longpimpled rubbers with flexible pimples and good spin reversal which gives most effect. The flexibility of the pimples are promoted by soft, long, thin, widely spaced out pimples and a thin rubber base. These are also things which makes the pimples easy to brake.
Control
Long pimpled rubbers with the shortest pimples, which also are wide and dense packed have the best control. A thick rubber base also increase the control. This is true when you do something actively with the ball. Let us call this “offensive control” in contrast to “defensive control” which means control of spin or speed. The more spin reversal the better control concerning spin and the better ability to bend the pimples have, the better control in the sense of reducing speed.
Speed
The characteristics which gives “offensive control” also gives high speed with one exception and that is “catapult speed” which is created with long elastic easily bending pimples.
Spin
A rubber mixture which gives friction on the pimples surface and ribbed surface increase the possibility to produce spin but the possibilities are rather small compared to a pimples-in rubber or even a short pimpled rubber.
The role of the sponge and the blade
If you add a sponge to the topsheet you will normally loose control , spinreversal and wobbling effect. What you win is attacking and lifting capacity. With a thicker sponge it is much easier to hit. A hard blade will increase the spin reversal and a soft blade will increase the control and diminish the spin reversal.
Conclusion – the racket
The most deceptive long pimple racket and the one with most spin reversal and wobbling effect is with a red hard, rather dense pimpled rubber without sponge on a fast blade. The most easy handled attacking combination is a black soft rubber with rather thick soft sponge on a soft blade. For pure control a rubber with good spin reversal without sponge on a soft blade is the best.