Prediction and Estimation of Power of a Tennis Racket with Wheels Replacing Conventional Grommets 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 palyer. 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 a new type of racket appeared in the market with wheels 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 new type racket and the conventional lightweight racket. Although this new type racket provides higher coefficient of restitution at the nearside of string face than any racket currently in the market, it needs more improvement in topside performance relevant to the power. Nevertheless, it may have a more comfortable feel at the racket handle than the conventional, which will be reported in a separate paper.