SECOND SECTION: WHAT REALLY CHANGES BETWEEN THE SURFACES
Now that basics of bounce physics are clear, we can explain furtherly why court speeds also depend on the shots themselves. For years, we believed to the alleged conspiracy of tournaments, which would make all surfaces the same to favour the best players. The reality is a little bit different, and the “blame” (if one can speak of blame) seems to be attributable much more to racquet manufacturers, who have designed tools with which it is much easier to play with heavy topspin, and also to the coaches, who oversaw the advent of the current playing style. If all courts appear to be alike, it is because most players use high levels of rotations. Both computer simulations carried out by the formidable Twitter user @fogmount (take a look here) and the analysis carried out – with a video camera – by the aforementioned Rod Cross team confirm a fairly unspoken truth: there is much more difference between the surfaces if we examine flat shots (with a small angle of impact) as there is by comparing the yield of topspin shots (which have a larger angle of impact). We use the data and diagrams published by @fogmount to present this evidence, but we can confirm that the same conclusions emerge from Rod Cross’s research, which is based on data obtained from real experiments.
Bounce simulation of a flat shot
This is a computer simulation of a shot hit at 80 mph with no topspin on clay and on grass. On the dirt, the ball would reach the baseline about 5,1 mph (-14%) slower, with about 0.05 seconds of delay and one foot higher.
Bounce simulation of a topspin shot
This is instead the simulation of a shot executed with 4000 rpm (rotations per minute, Nadal can even reach 5000), once more hit at about 80 mph. As can be seen, and perhaps against all expectations, the ball reaches the baseline after bouncing at virtually the same speed and after the same amount of time (the difference is just one millisecond). In terms of bounce, however, the difference between the two surfaces remains consistent, being about between 1 and 1,64 feet in height in favour of the clay.
