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. The aspect ratio is arrived at by dividing the length of the pimples by the breadth — a sheet with pimples of 1.8mm length and 1.7mm diameter will have an aspect ratio of 1.06. To be approved the aspect ratio is not allowed to exceed 1.1. This in effect means that very long and thin pimples are not permitted. Most pimpled rubbers today have a length of between 1.5mm and 1.8mm. On the 2005 ITTF list of Authorised Racket Coverings there are 79 different long pimpled rubbers listed.
The most deceptive long pimple rubber and the one with most effect is red, hard, without sponge and on a fast blade, so that the ball springs off the blade very quickly. Many players don’t understand that what is happening is that they are in effect getting their own spin back. If they for example put heavy backspin on the ball and the opponent pushes the ball back with the pimples, the return will not have backspin (even though his or her stroke is down and forward) but an element of topspin. A long pimpled rubber with a thicker sponge will usually return the backspin ball as ‘float’, while the rubber without sponge can send back a ball with considerable topspin.
Once you understand the above then all the rest of the ‘hype’ about long pimples is very much simplified. So-called spin reversal becomes obvious, you play topspin you get back backspin, you push you get back topspin. Whatever the opponent does with his or her racket is largely immaterial. Even the ‘wobbling’ balls are easily explained — these occur when you play with a none-pure spin, when for example you loop with topspin and sidespin (as most of us do) and you get back a backspin ball with a sidespin ‘kick’, simply because there are two different axes both trying to assert themselves at the same time. The most important consideration when playing against long pimples is not what the opponent is doing with his or her racket, but what you did with your last stroke.
Another factor that many players and coaches overlook is that power also affects the return ball. The harder you hit the ball with a closed racket, the more spin you create. Thus the harder you hit the ball against long pimples, the more backspin you get back on the return ball. It is often a better tactic to play slower balls or balls without spin to this type of rubber.
Of course there are one or two other aspects to consider – with some long pimples it’s easier to play short or low returns or even initiate some spin. Certain players are able to get much more effect from their pimples than others. The sponge (if used) will also have a considerable impact on what you can do with the rubber. A rubber without sponge will have maximum return effect, thin sponge will often have more control (but less effect) and it’s much easier to hit with thicker sponge.
The long pimpled rubbers with the most pronounced anti-spin (or spin reversal) effect are quite hard and the individual pimples feel more like ‘plastic’ rather than rubber.
The most pronounced effect is usually where the pimples are more widely spaced and less ‘rubber’ comes into contact with the ball. The flexibility of the pimples can also give unusual reactions but of course very soft pimples are easily broken.
Where long pimples are shorter, wider and more densely packed the control and spin elements will usually be higher. These are of course the reverse characteristics to the more ‘anti-spin’ types of long pimple. A thicker rubber base will also give a slower rebound speed and more control as will a thin layer of sponge. Softer pimples which are more flexible can help in returning balls short on the opponent’s half of the table.
We must really define what we are talking about in terms of speed off the racket. Pimples with no sponge will give very quick recoil from the wood of the racket and at times it may be difficult to control hard loops. Pimples with medium or thick sponge will have a slower rebound from the racket and it can be easier to control topspin.
Some pimples have a ribbed or rough surface and therefore have the capability to produce spin. This is still relatively small when compared to the spin created by reverse or some short pimpled rubbers. Often too the softness of the pimples or sponge or the thickness of the sponge will play a much larger roll in creating spin than the actual surface of the pimples.