A customer with an SW1 recently asked if it matters whether the racket is oriented with the head perfectly vertical, for swingweight, or perfectly horizontal, for spinweight measurements. I suspected that the result wouldn’t be very sensitive, but I wanted to quantify it.
I modeled a racket in CAD and adjusted the material densities to get a string bed of 17 grams and overall mass properties close to a typical tennis racket:
- Mass: 333.5 grams
- Balance: 33.2 cm
- Swingweight: 306.8 kg·cm²
- Twistweight: 13.6 kg·cm²
Then, I twisted it in 1° increments and output the moment of inertia about the swingweight axis:
|Twist (°)||Swingweight (kg·cm²)||Difference (kg·cm²)|
From the data, it seems unnecessary to be extremely accurate with racket orientation for typical swingweight measurements. At 5° of twist, which is easy to see, the swingweight result is only off 0.1 kg·cm². However, if measuring swingweight and spinweight to determine twistweight from the difference, orientation accuracy is more important. An error of 0.1 kg·cm² is more significant relative to the magnitude of twistweight.
These results should be valid for any swingweight measurement method.
If you have any questions about the SW1 or racquet measurement, leave a comment below.