Wet Tennis Balls

Someone I string for commented that he could not control the ball in slightly wet weather.

My reply was tennis was meant to be played in dry conditions.

Nevertheless, here's my thoughts on how wet balls affect the strings...

All of the above six balls weighed 59 grams when dry. 

The top three balls were soaked in water for ten minutes before weighing. The bottom three were rolled around on a wet floor.

The average weight of the top three and bottom three was about 73 grams and 68 grams, respectively, with a difference of about 5 grams.

Compared with dry balls, the top and bottom weighed an extra 14 grams and 9 grams respectively.

All these were static measures on a stationary ball. The difference is perceptible but insignificant.

However, once the ball starts moving at high speeds, the additional weight increases its momentum very significantly.

Momentum = Mass x Velocity

Without getting too much into detailed calculations, a simplified version looks like:

Dry Ball Momentum = 59 grams x 50 mph

versus

Wet Ball Momentum = 73 grams x 50 mph

And that's only for the average rally speed in tennis. For serves, the speed often increases to 100 mph, or more. Even for many recreational players.

When tensioning, I often take into account the players' footwork, tempo, racket head speed, string pattern, string gauge, choice of string, etc. And all these are based on DRY conditions.

Can you imagine what would happen, after all the weight measurements were taken, and the appropriate bungee cord attached for that single person, then three jumpers just decided to strap together to jump?

Of course there are other factors, like the wet felt on the ball reducing ball-to-string friction, the wet court affecting bounce, and the fluffed up fur changing trajectory. 

But to me, the huge increase in momentum delivers the biggest impact to the stringbed. Which was why I liked using damp balls to train myself before playing with a heavy hitter last time.

In addition, after the extra stress from playing with wet balls, the stringbed would usually lose too much tension thereafter.




     

Lubricating Strings

Following my previous attempt to increase spin by increasing ball-to-string friction (link), I thought I should try reducing string-to-string friction as a comparison too.

Roughing up the strings severely reduced durability. In some instances, I did not even get to play before it snapped! So it was not very viable.

Reducing inter-string friction would mean using lubricants like grease, silicone and hand lotions.

Almost equal amounts of each of the three different lubricants were applied directly onto the strings of three different rackets. Then rubbed into the intersections between mains and crosses. Excess amounts were lightly wiped off using tissue paper.

Knowing upfront that the tennis balls would be gunked up with oily residue, old tennis balls were used. They were playtested, then checked for bounce height and weight to ensure equality. 3 balls were set aside to test each lubricant independently.

Unfortunately, it was a total disaster.

Despite wiping off the excess lubes, the balls turned greasy very quickly. Once that happened, the entire stringbed became so slippery. Any attempts to swipe the ball for more spin ended up having the ball skid off the strings instead. There was no grip at all.

The few times that the strings managed to grab the ball did not end up well too. Directional control was lost. The ball zipped off sideways before the stroke was completed.

The hand lotion posed the least problems and the oils were all equally bad. Not only were all the balls ruined in less than 15 minutes, but my hitting partner's stringbed turned oily and lost grip as well. Our overgrips, pockets and shirts were also stained. 

Some faint ball marks could also be seen on the dry hard court. Out of safety and consideration for other users, we stepped over the ball marks to ensure they were not slippery. We looped a rag under one shoe and cleaned up as many ball marks as we could find.

After cleaning up, we resumed playing our normal games with normal rackets and balls. 

If you do attempt this, please ensure to:
(1) bring lots of rag to clean up the mess,
(2) change new overgrips as my racket almost flew, and
(3) check that the courts are not slippery for the next user.

But seriously, this is not worth trying.

Pressureless and Pressurized Balls

On the left was a pressureless Wilson Trainer ball. On the right was a pressurized Wilson US Open ball.

The overall thickness of both rubber cores were similar. When new, their weights and bounce were similar too.

What differed was that while the trainer ball had a single rubber core, the US Open had dual layers of rubber, one dark brown and one white.

Just sharing, if you are curious...

Pressurized Ball Savers

Following this post (link), I recalled my previous attempt to build and test the efficacy of a pressurized ball saver. 

(Thanks to M, who sponsored most of the materials earlier)

I had wanted to test it out on several different brands of balls together, but the stores was left with only one. While waiting for stocks to replenish, this completely slipped my mind.

So now, this is picking up steam again...

Objective:
- To test if used tennis balls with a diminished bounce could be restored to regulation play (link).

Methodology:
- Three different brands of pressurized balls were used.
- Two cans were bought per brand. Total 18 balls.
- Within each brand, 2 balls were set aside unused outside its container to let it deflate. The other 4 balls were used for matchplay. 
- All balls were marked for easy identification later.
- Bounce height from a 100" drop was measured for all balls when new and used.

Here's how my DIY pressurized PVC tube looks like. If you're planning to build one, there's plenty of instructions available online.

This tube could hold about 15 balls. I filled it with:
- 6 used balls from 3 different brands,
- 6 unused but deflated balls from 3 different brands,
- 2 pressureless balls, 1 used, 1 new.

Then it was connected to an air compressor set to 20psi. The auto-regulated air compressor eliminates the need to check and re-pump air regularly. It also ensures the balls are subjected to a constant air pressure throughout.

The balls were left in there for a week, then taken out to test its bounce before being put under pressure again. This cycle was repeated for four weeks.

Results:
- For both pressureless balls, there was no difference at all in their bounce at any point in time.
- Among the 6 used balls, a slightly higher bounce was observed in 2 balls in the drop test. When played on the tennis court, they still felt a little flat compared to those fresh from the can. There was no change in the other 4 used balls.
- All 6 unused but deflated balls registered a higher bounce than before, although to different degrees. The air pressure held well during play but still, they could not pass off as new.

Please note this was never intended to be an exhaustive nor conclusive test of pressurized ball savers, or tennis balls. It's more to satisfy my personal curiosity.

A Little Ball Tip for Greater Comfort

For some who suffer from shoulder, wrist or elbow pain from tennis, I thought I'll share a little tip I picked up from some senior playing partners.

Instead of using pressurized balls, convert to used Wilson Trainers.

Somehow, these Wilson trainers almost never lose their bounce. I've tested their bounce when new, and after 20+ hours. The drop was insignificant.

When new, most of them weighed about 59g. Quite consistently. And depending on how much fur was lost, I've seen some drop to as low as 49g.

But the best part was, these trainers' rubber rarely hardens up as much as other balls. And the lighter version played and felt the same as the heavier version, less the shock.

So, to lessen the shock to our arms during impact, use slightly lighter balls. The group of seniors really liked those about 52-55g. 

(ITF stipulates the ball must weigh at least 56.0g (link)).

Or, if you wish, try shaving some fur off that new can of pressurized balls to 56g before playing. Your arm would feel the difference!

Along with this, you can also safely drop a few pounds of tension without suffering any loss of control.

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.