Prediction and Estimation of Power of Tennis Rackets with Clamped Strings Compared to those with Wheels on the Sides

Currently, the terms used in describing the performance of a tennis racket are still based on the feel of an experienced tester or a player. However, the optimum racket depends on the physical and technical levels of each user. Accordingly, there are a number of unknowns regarding the relationship between the performance estimated by a player and the physical properties of a tennis racket. The lightweight racket with head-heavy configuration is recent tendency of high-tech rackets, increasing power with an increasing racket swing speed. Racket frames as light as 200 grams have appeared in the market. However, the predicted results showed that the lightest racket at present in the market has advantageous for racket head speed, but disadvantageous for coefficient of restitution, rebound power, and post-impact velocity for ground stroke, and it has also large shock vibrations at the racket handle compared to the ordinary super-light weight racket. This means a limit to the weight lightening of tennis racket from the viewpoint of performance. The engineers and racket designers at the racket companies seem to be under intense pressure to keep pumping out new and better technologies every year. This paper investigated the physical properties of new type of rackets appeared in the market with wheels or with clamped strings by contraries replacing conventional grommets on the sides, predicting racket performance in terms of the coefficient of restitution, the rebound power coefficient, and the post-impact ball velocity relevant to the power of the racket. It is based on the experimental identification of the racket dynamics and the simple nonlinear impact analysis. The predicted results could explain the difference in mechanism of performance between the two new type rackets. Although the racket with clamped strings provides higher coefficient of restitution around the center of strings face than the racket with wheels on the sides, there is no big difference in the performance relevant to the power. The shock vibrations at the wrist joint relevant to the comfort or feel will be reported in a separate paper.