What About Tennis Balls?

In soccer, the official match ball undergoes regular updates. The most recent ball received an aerodynamic change that initially baffled quite a few players about its flight path. (link1)(link2)

In golf, ball manufacturers are always tweaking the dimple size, patterns and density to make it fly further and straighter and make it land softer. (link)

But what about the tennis ball?

Despite having more rules governing tennis balls than strings, we still see a huge plethora of different types of balls.

Some have thicker felt while others are denser. Some diameters are very slightly larger and a gram or two heavier. And the most commonly discussed was how they played - stiff, comfortable or mushy.

But not many pay attention to how fast the tennis ball deteriorates during play.

Let me recount an interesting incident.

A young chap contacted me and asked if I could help or teach him how to check a freshly strung stringjob. What should he lookout for? How does he know if it was consistent and well done?

From our conversation, I could tell he was very committed to the game and undergoes regular coaching sessions and matches. 

He handed me two freshly strung rackets with gut/poly and told me where it was done. I know the stringer. He does an excellent job. I checked the stringbed frequency, hoop length and width, knots, stringing patterns and others like string burn and grommet wear. Everything was perfect.

His chief gripe was very rapid loss of control. Then I asked about the type of balls he used. Mostly, it's fresh from the can slazenger wimbledon ultra vis. Sounded good to me until I found out their regular singles tennis sessions lasted 3 to 4 hours. 

With ONE can of new balls. 

In pro matches, balls are changed every 9 games (link). That's approximately 20 to 30 minutes of hitting. Even if we do not hit as hard as pros, I thought 3 to 4 hours was excessive.

Sometimes his partner brings a different brand, so I got him to set aside one of each type of ball after one hour of play, and pass it to me. In a single four hours session, they used four different cans of balls for an hour each.

Then I did a simple compression test for all the balls.

Ball/Diameter Before/Diameter compressed under 10kg
A/59/44
B/62/48
C/62/52
D/62/50

Only ball C passed the bounce test (about 56") when dropped from 100" (link). The rest bounced between 45" to 50".

Since the stringbed returns about 95% of the power and tennis ball returns about 55% (link), a flat and soft ball would compress more during impact with the strings and absorb more power compared to a fresh ball.

And when this player saw his balls landing shorter, he swung much harder which led to his "loss of control". Nothing to do with my friend's excellent stringjob!

For those who are keen, I just found out from an article that Slazengers seem to have a very wide variance in performance when fresh and after play. Compare the purple line for Slazenger in the 3rd and 2nd chart from the bottom. (link)

In contrast, Dunlop and Penn balls seem to last pretty well after play.