You may have noticed in some recent videos on my YouTube channel that I’ve been trying to find a way of measuring the stiffness of squash rackets.
Well, here’s my method:
The app mentioned in the video is called RacquetTune. I used it on an iPhone. Thanks to Tjeerd for the tip on this app.
Anyhoo, feel free to give this app a try or shoot holes in the method!
Update, January 2018
Couple of interesting food-for-thought comments on the YouTube video.
Hi Pierre, I’m totally with you regarding an objective measurement for stiffness! However, watching your video I noticed several possible pitfalls or at least factors that might influence your interpretation of the results. Although I don’t have the RacquetTune app myself or are otherwise affiliated with it, it’s pretty clear that it uses sound (pitch) to produce some stiffness/tension number. So, what you need to take into account are the following: 1. The thing you hit the racket with. You use a hollow PVC pipe. Especially since it’s hollow, the pipe itself will prodoce some sound of specific frequency/frequencies. If you’d use a different thing to hit your racket with, you’ll get different results. Try it. 2. The way you hold your racket. In this video you held it softly near the grip/throat of the racket. If you hold it softly (which you did), you’ll allow more of the pipe’s kinetic energy to transfer to kinetic energy of the racket in total, rather than vibrating the molecules of the racket. Or in other words, the softer your grip on the racket as you hit, the more it will swing in some direction and the less it will vibrate. It’s the vibration of the racket that in turn vibrates the molecules in the air, which is the sound the app is interested in. 3. Stringing tension should play a role. Probably mostly due to vibration of the strings themself as you hit the racket, adding to pitch that the app measures. Other things like the material of the frame might also play a role, but then again, the material would also play a role in the stiffness. So it’s hard to say whether that needs disentangling. Anyway, the way you use the app now, does probably not lead to an objective outcome. But it could be effectively used in comparison. If you hit each racket exactly the same with the same material, you might be able to say: “this racket’s stiffer than that one”.
Hi Pierre, nice idea to use the frequency method to deduce stiffness for squash rackets! However, when using frequency as your method you must also take into account the weight of the racket. A higher weight will produce a lower frequency and a lower weight produces a higher frequency. This means that two rackets that do have the same stiffness, but differ in weight, will produce different results. To get more accurate measurements you should multiply your measured frequency with the racket weight. That will give you comparable results from this method.
Update, November 2018
I ran some tests to see how the same racket might yield different stiffness outcomes. The tests were done on this Unsquashable Y-Tec Pro:
First I hit the racket with the official Squash Source whacking stick, which is a 3/4-inch PVC pipe:
This give us a baseline stiffness reading of 140 Hertz.
Next I hit the racket with the business end of a ball-peen hammer, or as I prefer to call it, a heat-treated forged high-carbon steel hammer:
Result: 140 Hz. Same.
Next I tried a rubber mallet:
Result: same. 140 Hz.
Next up, this metal tool. I have no idea what this tool is used for. Some sort of pipe wrench? I found it in my basement.
Result: about the same, 139 Hz. That’s less than 1% difference from the baseline.
Next up, a wooden dowel:
Result: about the same, 139 Hz.
Next, I measured the stiffness by hitting the racket with another racket. SO META.
Result: about the same, 139 Hz.
Then I tried hitting the racket with the butt end of a screwdriver:
Result: same, 140 Hz.
How about adding an overgrip?
Nope, still 139 Hz.
How about one of those little shock absorbers like the kind that come on Dunlop rackets?
HANG ON HOUSTON, we have a new development here: 136 Hz. This is a little over 2% lower than the original reading. Honestly, I’m not even sure I understand this. Adding a shock absorber makes the racket feel less stiff?