Have you ever noticed how regular tennis balls tend to go soft after awhile? That’s because they are filled with a pressurised gas, which is what gives them their zip and bounce. Unfortunately this gas gradually dissipates under normal atmospheric pressure, which is much lower than the balls’ internal pressure. And in case you were wondering, that’s the reason regular tennis balls are sold in pressurised cans.
How long does it take for them to go flat? Not very long at all, unfortunately – according to a study by Wilson, not more than about two weeks.
This is obviously not good news for owners of tennis ball machines. Think about it: if you set your machine to deliver a ball every five seconds and load it up with 100 balls, how much use will each ball get? Well, if you play constantly for an hour, you’ll hit 720 shots – around 7 shots per ball. But that doesn’t allow for rest breaks or pausing to reload the machine, so in reality it’ll be a fair bit less than that. Bottom line is your balls are going to be barely used after a session, and unless you’re using your machine every day, you’ll find the balls going flat before you’ve had decent use of them!
Pressureless tennis balls
The answer is pressureless tennis balls, also known as practice balls. Whereas a regular ball gets its bounce from being filled with highly pressurised gas, a pressureless ball has an internal pressure not much different to atmospheric pressure. By contrast it gets its bounce from the structure of its rubber shell, and thus does not lose bounce over time. In fact, if anything a pressureless ball gets more bouncy as its fur wears down and it becomes lighter. However, this process is much slower than the decay of pressurised balls, and allows you to get full use of the balls before having to replace them.
Pressureless balls can be a little more expensive than the regular kind, but when you consider how much less frequently you will need to replenish your supply, it’s a worthwhile investment that will save you a lot of money in the long run. All the major tennis ball manufacturers have a pressureless offering – Dunlop, Slazenger, Wilson, Penn – and all naturally claim that theirs is the best. But Tretorn seems to have the edge in this market with their “micro cell” technology which they claim results in a ball with all the benefits of being pressureless, but also performs like a regular pressurised ball.
My advice is to try a few different kinds and see what works for you. Frankly, most recreational players are not going to be that bothered about minor differences in performance – the important thing is balls that are durable and provide consistant bounce.