Here's a question I get a lot from juniors (and from their parents, usually holding a snapped racket): what does the number on the stringing machine actually mean? Forty-eight pounds. Fifty-eight pounds. Same frame, same strings, same player — but a completely different feeling racket. Let's unpack what's physically happening, because once you understand it, you stop guessing and start choosing.

The spring in the bed

When a ball lands on your strings, the strings stretch and then snap back — they're a spring, not a trampoline. The tension is just how tightly that spring is pre-loaded. Tight strings stretch less on impact; loose strings stretch more.

That extra stretch matters because of something called dwell time. On a looser stringbed, the ball sits on the strings a fraction longer and the strings pocket it deeper. On a tighter bed, contact is shorter and the stringbed feels firmer, almost like a board.

Which one sends the ball further? Counter-intuitively, it's the tighter bed that tends to launch higher and longer, because the strings snap back harder and more of the energy goes into forward pace. The looser bed absorbs more of the impact, so the ball comes off slower — but with more spin, because the pocketing lets the strings grip and roll the ball's nap.

Spin: the loose-string advantage

This is the bit most players feel before they can explain. Looser strings, more spin. That's largely a snapback story. When you brush up the back of the ball, the main strings (the vertical ones) deflect sideways, then slide back into place as the ball leaves. That sideways slide-and-snap is a big part of what we call string spin. Looser strings slide further and recover faster, so you get more of it.

Tighter strings slide less, so less snapback, less free spin — but more control. The ball comes off predictably because the bed isn't flexing wildly under it. That's why big flat hitters often like it stiff, and why clay-court grinders with heavy topspin often drift looser.

So why does 48 feel nice and 58 feel harsh?

Two things happen at higher tension. First, the stringbed deflects less on off-centre hits, so the shock goes into your arm instead of being absorbed. Second, the window between 'ball lands in' and 'ball flies long' gets narrower. A tight bed punishes a late swing more sharply — the ball goes where the racket face says, not where your intent says.

At lower tension you get a bigger, more forgiving sweet spot and a softer feel, but the launch angle gets higher and less consistent. You might find your forehand suddenly sailing. That's not you; that's the spring.

The rule of thumb (and why it's only a rule of thumb)

A useful starting idea: tight = control and flat, loose = spin and comfort. But the number is not the whole story. String type matters as much as tension — a stiff polyester at 48lb can feel firmer than a soft multifilament at 58lb. Racket head size and string pattern change the effective stiffness too. A dense 18x20 pattern at 50lb plays tighter than an open 16x19 at the same number.

And tension drops after stringing. Strings relax as they're hit, especially the first few hours. That's part of why a fresh restring feels so crisp and then 'goes off' after a week or two of play. It's not your imagination.

Take it to court

1. Change one thing at a time. Drop or raise tension by 2–3lb, keep the same string, and play a full session before judging. Big jumps tell you nothing. 2. Match tension to your game, not your hero's. If you hit flat and want control, go tighter. If you brush heavy topspin and want a bit more bite and comfort, go looser. Your elbow will thank you either way. 3. Restring on a schedule, not on a snap. Strings lose their liveliness long before they break. If you're training several times a week, a fresh bed every few weeks is worth more than any gadget.

Get curious about the number. It's the cheapest piece of equipment tuning you own.