Technical Tennis Racquets, Strings, Balls, Courts, Spin, and Bounce Rod Cross Crawford Lindsey Racquet Tech Publishing Vista, California, USA Copyright © 2005 by Rod Cross and Crawford Lindsey Racquet Tech Publishing (An imprint of the USRSA) 330 Main St. Vista, California 92084 www.racquettech.com All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, elec- tronic, mechanical, photocopying, recording or otherwise, without the express written consent of the publisher. Library of Congress Control Number: 2005905393 Cover design and illustrations by Kristine Thom Inside chapter title photos by Ron Waite, Photosportacular Printed in the United States of America ISBN-13: 978-0-97227-593-4 ISBN-10: 0-9722759-3-2 Contents FOREWORD . . . . . . . . . . . . . . . . . . .v The Six “Weights”of a Racquet . . . .28 Racquet Weight . . . . . . . . . . . . . . . . . .30 PREFACE . . . . . . . . . . . . . . . . . . . .vii Light vs Heavy Racquets . . . . . . . . . . .33 Ideal Racquet Weight . . . . . . . . . . . . .34 1RACQUETS Balance Point and Pickupweight . . . .36 Swingweight . . . . . . . . . . . . . . . . . . . . .38 Twistweight . . . . . . . . . . . . . . . . . . . . . .41 INTRODUCTION . . . . . . . . . . . . . .1 Spinweight . . . . . . . . . . . . . . . . . . . . . .42 Choosing a Racquet—the Basics . . . . . .1 Hittingweight (“Effective Mass”) . . . .43 Mistakes When Buying a Racquet . . . . .3 Three Types of Racquet . . . . . . . . . . . . . .3 STIFFNESS (FLEX) . . . . . . . . . . . . . . .44 Racquets and Player Psychology . . . . . . .5 Racquet Stiffness . . . . . . . . . . . . . . . . .44 Racquet Features Combine Measuring Racquet Stiffness . . . . . . . .45 with Strokes . . . . . . . . . . . . . . . . . . . . . .7 Match Point Box 1.4:Vibration Selecting a Racquet Is Art & Science . . .9 Comparison between Racquets . .46 Care of Racquets . . . . . . . . . . . . . . . . . . .9 Racquet Vibrations,Sweetspot, and Feel . . . . . . . . . . . . . . . . . . . . . .48 RACQUET PROPERTIES . . . . . . .10 Vibration Dampening . . . . . . . . . . . . .50 POWER . . . . . . . . . . . . . . . . . . . . . . .11 Shock & the Center of Percussion . .51 The Components of “Power”: Match Point Box 1.5:The Difference Exit Speed,Rebound Speed, between Shock and Vibration . . . .55 Racquet Speed . . . . . . . . . . . . . . . . .13 Match Point Box 1.1:Effect of CUSTOMIZING A RACQUET . . .56 Grip Firmness on Power . . . . . . . .15 Match Point Box 1.6:Customizing The Maximum Exit Power Point Weight,Balance,& Swingweight . .57 Changes with Racquet Speed . . . .17 Further Reading . . . . . . . . . . . . . . . .58 Comparing Racquet Power . . . . . . . .19 2 STRINGS Racquet Power Defined as Rebound Power . . . . . . . . . . . . .21 Match Point Box 1.2:Maximum Effort Power . . . . . . . . . . . . . . . . . . .22 STRINGS AND Rebound Power Is the Sum THE MODERN GAME . . . . . . . . .59 of All Racquet Properties . . . . . . . .24 Power and Energy Loss . . . . . . . . . . .25 STRINGBED STIFFNESS . . . . . . .61 Match Point Box 1.3:Maximum Static & Dynamic Stringbed Stiffness . .62 Theoretical Ball Speed . . . . . . . . . .25 Effect of String Material and Gauge The Bad News:Rebound Power Values on Stringbed Stiffness . . . . . . . . . . . .66 Aren’t Readily Available . . . . . . . . .26 Effect of String Tension on Stringbed Stiffness . . . . . . . . . . . . . . . .68 CONTROL . . . . . . . . . . . . . . . . . . . . .27 Effect of String Pattern on Rebound Control . . . . . . . . . . . . . . . .27 Stringbed Stiffness . . . . . . . . . . . . . . . .71 Effect of Headsize and Stringbed WEIGHT . . . . . . . . . . . . . . . . . . . . . .28 Suspension System on Weight and Apparent Weight . . . . . .28 Stringbed Stiffness . . . . . . . . . . . . . . . .71 iii Contents Match Point Box 2.1:Rise in String BALL BOUNCE OFF Tension During a Shot . . . . . . . . . . . .72 THE STRINGS . . . . . . . . . . . . .108 Stringbed Stiffness Summary . . . . . . .73 Angle of Impact . . . . . . . . . . . . . . . . . .109 Tilting the Racquet Head . . . . . . . . . .113 TENSION AND The Bounce Path off the Strings . . . .113 PERFORMANCE . . . . . . . . . . . . . .74 Further Reading . . . . . . . . . . . . . . .117 Tension and Power . . . . . . . . . . . . . . . . .75 Tension Loss and Going “Dead” . . . . .77 4 SPIN & Tension Loss and Feel . . . . . . . . . . . . . .78 TRAJECTORY Tension Loss and Control . . . . . . . . . . .79 Tension Loss and Sound . . . . . . . . . . . .79 SPIN BASICS . . . . . . . . . . . . . . . .119 Tension Loss and Prestreteching . . . . .79 Generation of Spin . . . . . . . . . . . . . . .120 Tension and Spin . . . . . . . . . . . . . . . . . .80 Influence of Incident Angle and Spin Tension and Player Perceptiveness . . . .80 on Rebound Spin . . . . . . . . . . . . . .121 Match Point Box 4.1:Effects of Spin DWELL TIME AND on Bounce off the Strings . . . . . . . .121 PERFORMANCE . . . . . . . . . . . . . .82 Types and Uses of Spin . . . . . . . . . . . .123 Dwell Time . . . . . . . . . . . . . . . . . . . . . . .82 18 Different Ways to Hit the Ball . . .126 Dwell Distance . . . . . . . . . . . . . . . . . . . .84 Spin Before and After Bounce . . . . . .127 Dwell Error . . . . . . . . . . . . . . . . . . . . . . .85 Effect of Grip on Spin . . . . . . . . . . . . .128 Dwell Time and Force . . . . . . . . . . . . . .85 Can Racquets and Strings General Rules of Dwell Time . . . . . . . .86 Increase Spin? . . . . . . . . . . . . . . . . . . .130 Further Reading . . . . . . . . . . . . . . . .86 Match Point Box 4.2:Can Players 3 BALLS & Feel Spin . . . . . . . . . . . . . . . . . . . . . . .131 Increasing Spin with BOUNCE Stroke Technique . . . . . . . . . . . . . . . .132 Simple Topspin Experiment . . . . . . . . .133 BALL BASICS . . . . . . . . . . . . . . . .87 Match Point Box 4.3:Topspin and Ball History . . . . . . . . . . . . . . . . . . . . . . .87 the Federer Forehand . . . . . . . . . . . .134 Rules about Balls . . . . . . . . . . . . . . . . . .87 Effect of Racquet Tilt on Match Point Box 3.1:Ball Testing a Topspin Forehand . . . . . . . . . . . . . .137 to Compare New and Old Balls . . . .89 Pressurized and Pressureless Balls . . . .90 SPIN AND THE SERVE . . . . . . . .139 Ball Toss . . . . . . . . . . . . . . . . . . . . . . . . .139 BALL BOUNCE OFF Tips on Serving . . . . . . . . . . . . . . . . . .140 THE COURT . . . . . . . . . . . . . . . . .90 Arching the Back to Serve . . . . . . . . .142 Friction . . . . . . . . . . . . . . . . . . . . . . . . . . .91 Slice Serve . . . . . . . . . . . . . . . . . . . . . . .144 Bounce Factors . . . . . . . . . . . . . . . . . . . .93 Serve Actions . . . . . . . . . . . . . . . . . . . .144 Bounce Factor #1: Forearm Slows Down . . . . . . . . . . . . .145 Angle of Incidence . . . . . . . . . . . . . . . .94 Match Point Box 4.4:The Bounce Factor #2: Sampras Serve . . . . . . . . . . . . . . . . . .146 Incident Speed and Spin . . . . . . . . . . .95 Force on Handle . . . . . . . . . . . . . . . . .147 Bounce Factor #3: Hardness of Court . . . . . . . . . . . . . . .96 TRAJECTORY . . . . . . . . . . . . . . .148 Bounce Factor #4: Vertical Launch Angle . . . . . . . . . . . . .148 Court Smoothness or Roughness . . .98 Hitting the Ball Deep . . . . . . . . . . . . . .150 Horizontal Bounce Speed . . . . . . . . . . .99 Further Reading . . . . . . . . . . . . . . .152 Effects of Friction on Ball Spin . . . . . .102 iv Foreword Several years ago, the two authors of this book and I wrote an encyclopedic tome with the imposing title The Physics and Technology of Tennis. Even though thousands of copies of this book have been sold and are still selling, and in spite of the fact that it was a Scientific American Book Club selection, it is not for everyone, and only the most motivated have read it from cover to cover. Who ever thought there was so much science to hitting a fuzzy yellow ball? But there is, and it is all there in its 435, 8.5” x 11” pages, including many hun- dreds of graphs, charts, diagrams, and formulas. It is a tremendous reference book, textbook, or self-teaching manual, but it is not a casual read. What is needed now is an up-to-date, reader-friendly book that covers the technical parts of tennis in a far less comprehensive and technical manner. It needs to be written so that a tennis player can pick it up, read it, and under- stand it. This is that book. It is written for tennis players and tennis fans, not engineers, scientists, or over-motivated super-achievers. It is still meaty and an intellectual adventure, but all the technical language has been translated to people-speak within its human-sized 160 pages. It addresses questions such as: • When you want a bit more power in your game, should you go to a heavier racquet or a lighter one? • What are the advantages of a racquet that has a bigger head? • What effect does string tension have on your game, and how does it affect power and control? • What is the difference between gut strings and synthetic strings? • What is the importance of string thickness? • What is a “fast” court and what is a “slow” court? • Should you adjust your equipment to match the court speed? • When buying a racquet, what features should you look for? • If you want to put more spin on the ball, what should you do? In my many years of playing tennis and studying tennis, I have heard a lot of anecdotal answers to these questions. This book gives you the answers that sci- ence and technology provide. HOWARDBRODY Physics Department University of Pennsylvania v Preface Much has already been written about tennis, mostly about how to improve your mental and physical game and about famous players. This book is about neither of these topics. It is about racquets, strings, balls, and courts and how they interact with each other and with players. You can play a very good game of tennis (or golf or baseball) without knowing anything about the equipment you use or about ball trajectories, but being aware of the basics can help you avoid common pitfalls. In fact, it is amazing how many of today’s top players appear to be unaware of the basics. Watch them when they change ball direc- tion back over the net. They are very good at returning the ball straight back to their opponent, but as soon as they hit away from their opponent, their error rate increases dramatically. There is a simple reason for this. It is always safer to hit the ball straight back to your opponent because the ball will travel back in that direction no matter how hard you hit it. If you try to change the direc- tion of the ball, then the angle of the ball off the strings depends on how fast the ball is traveling toward you and on how hard you hit it. If you know about this, then you will be less likely to aim precisely for the sideline. Chances are, if you aim for the line, the ball will go out. If you know how and why you are doing a particular action, it may not direct- ly help the performance of the action, but it will enhance your mindset, which in turn influences the performance. If you know why, for example, that tilting your racquet face forward causes more topspin, then you will be more likely to practice doing it with confidence, without those nagging doubts that it is stu- pid and your instructor is nuts because you obviously can’t hit the ball over the net, with topspin no less, while “aiming” into the ground. If you know how much extra power, spin, or comfort you can or cannot get by changing string tensions or by using bigger racquets, then you will be able to make intelligent equipment decisions and not waste emotional and intellectual energy agoniz- ing over whether your trial-and-error guess of what’s best for you is really best. Changing strings, tensions, racquets, and customizing weights and balances then become fun, tactical elements of your tennis game, not spin-the-wheel whims of chance. Knowing what your equipment can and can’t do for you makes a big difference in how you approach the game. Knowing how, when, and why the ball grips the strings and how that affects your shot frees you from chasing solutions to getting “more grip” on the ball that not only don’t exist, but would have no vii Preface effect if they did. Understanding why a ball bounces as it does on a topspin, backspin, or sidespin shot enables you to ready yourself, get in position, and anticipate your return of the shot. It eliminates the frustration of being caught flat-footed and clueless time after time. It enables you to make intelligent cor- rections in your game. But most of all, knowing what actually happens during the hit, flight, and bounce of the ball and why it happens is just plain fun. To be able to explain how and why the court, racquet, and air affect the speed, spin, and direction of the ball—the very essence of tennis—and thus why strokes, tactics, and strategy have evolved as they have, is a rush matched only by being able to actually do these things. Knowledge and performance combine to provide a much deeper and enjoyable tennis experience, if not a more successful one as well. For readers who are interested in the technical and scientific aspects of tennis or are just plain curious or are looking for an extra understanding that will give strokes and shots meaning, this book has been written especially for you. It contains the results of many years of investigation and many experiments designed to extract the secrets of how and why tennis balls, racquets, and strings manage to behave the way they do. We still don’t know everything there is to know about the subject, but we know a lot more than we used to know. For example, we know very little about players’ perceptions of equip- ment properties and why they are so often quite different from actual measure- ments of those properties. Likewise, we don’t know why one player has a favorite string or racquet and another will think that particular string or rac- quet is the worst he or she has ever played with. Not knowing all the answers makes the search an adventure, finding them out is exhilarating, and applying them raises the level of the game. Many people have contributed to this book in many ways. We thank all of them profusely, especially Howard Brody, Ron Kohn, Paul Metzler, Greg Raven, Kristine Thom, Ron Waite, Nancy Crowley, and our wives Voula and Susan. viii Chapter One Racquets All racquet performance technologies boil down to two things—altering the stiff- ness of the frame and stringbed and the amount and distribution of weight. These, in turn, determine the power, control, and feel of a racquet. INTRODUCTION Hitting a tennis ball is an epic battle between player, racquet, and ball. The player ultimately wants to be able to swing the racquet as fast as possible and to change its direction in a split second, but he does not want the ball to be able to do the same thing to the racquet. He doesn’t want the ball pushing the racquet backwards, twisting it in his hand, or bending it out of shape and direction. But making it more difficult for the ball to move the racquet also makes it more difficult for the player to do so. For the player to achieve the most maneuverability, the racquet has to be light, but to prevent the ball from knocking the racquet all over the place, it has to be heavy. And if the ball is pushing the racquet around, power is lost. So, the player also wants the rac- quet to be heavy to get the most power. But if it is too heavy, he can’t swing as fast, and he loses power. What a problem! CHOOSINGA RACQUET—THE BASICS Given these problems, how does one choose a racquet? First we will start with some general common-sense principles and then get more specific. The hard- est part of buying a racquet is to find one that you like best. The problem is not that there are not enough to choose from. The problem is that there are too many (Figure 1.1). You could spend six months trying every racquet on the market, each at a few different string tensions, and you might still have trou- 1