TUNE TO WIN

by Carroll Smith

AERO PUBLISHERS, INC.

329 We.t Aviation Road, Fallbrook, CA 92028
 C AERO PUBLISHERS, INC. 1978

All rights reserved. This boolt., or flirts thereof, musl nol

be re/»"oduced without permissIon 0f'he publisher.

LIBRARY OF CONGRESS
CATALOG CARD NO.: 78-73549

ISBN 0-87938-071-3

Smith, Carroll
Tune to win.
Fallbrook, CA : Aero Publishers
p.
7812 781018

Printed and Published in the United States by Aero Publishers, Inc.

 DEDICATION

Since none of my friends who promised to write forewords came

through in time-and since we have allotted space for one and it's too
late to change now-there will be no foreword. Instead, I would like to
dedicate this one to my wife Jane, who has put up with a quarter of a
century of gypsy existence so that I could race-and to my children
Dana and Christopher, who have, I hope, enjoyed a somewhat unusual
childhood.
 PREFACE

In the preface to PREPARE TO WIN I threatened that, if the book were

successful, it would be followed by TUNE TO WIN.
Thanks to you, the readers, PREPARE TO WIN has been a modest
success-modest enough so that I have not thrown away my stop watches
and drafting tools but successful enough to motivate me to get started on
TUNE TO WIN.
I do so with a certain amount of reluctance. I am constantly reminded of
Eric Broadley's reply to a serious inquiry as to why no designer has written
anything resembling a comprehensive study of racing car design-
"Probably because no one is willing to expose the depths of his ignorance to
public view." Too true!
I am fully aware that much of what I have to say in this book is subjective.
I wish that my knowledge and wisdom were such that this were not so. Many
readers are going to disagree with my interpretations, conclusions and
recommendations. I offer no apology. In each case I will put forth my per-
sonal best shot on the subject at the time of writing. I reserve my right to
change my thinking at any time.
Our knowledge of any field whose title includes the word dynamics should
be constantly expanding. This is because, particularly in motor racing, we
approach a complex subject from a base of abysmal ignorance and also
because, in a field defined by compromises, knowledge gained in one area
can and does modify our thinking in related areas.
What follows is not intended to be a step-by-step instruction manual for
decreasing the lap times of a racing car. Rather it is intended to be a mind-
opening exercise-admittedly in a narrow field. If, at the end, the reader has
gained a better understanding of vehicle dynamics and a fuller appreciation
of the problems of control and response at high force levels, my primary pur-
pose will have been reached. If the reader is then able to apply this
knowledge to enhance his enjoyment of motor racing and/or increase his suc-
cess at it, the book will be a success.
 TABLE OF CONTENTS

CHAPTER ONE
Vehicle Dynamics-What's It All About? 9
CHAPTER TWO
The Racing Tire . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 13
CHAPTER THREE
Weight, Mass Load and Load Transfer. . . . . . . . . . . . . . . . . . . . . . . . . . . .. 27
CHAPTER FOUR
Suspension Geometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 41
CHAPTER FIVE
Steering Geometry and Self Steering Effects. . . . . . . . . . . . . . . . . . . . . . .. 60
CHAPTER SIX
Rates and Rate Control-Springs and Anti-Roll Bars. . . . . . . . . . . . . . .. 64
CHAPTER SEVEN
The Shock Absorber 74
CHAPTER EIGHT
External Aerodynamics 78
CHAPTER NINE
Cooling and Internal Aerodynamics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 97
CHAPTER TEN
The Brakes 107
CHAPTER ELEVEN
Understeer, Oversteer, Stability and Response 118
CHAPTER TWELVE
Tuning the Engine 140
CHAPTER THIRTEEN
The Drive Line 146
CHAPTER FOURTEEN
The Peculiar Case of the Large Sedan. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153
CHAPTER FIFTEEN
Racing in the Rain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 159
CHAPTER SIXTEEN
Putting It All Together 161
CHAPTER SEVENTEEN
Everything Else 165
CHAPTER EIGHTEEN
The End 169
 STATEMENT OF NON-LIABILITY

Our society has reached the point where I am advised that,

in order to protect myself from possible lawsuits, I should in-
clude a statement of non-liability in this book. Since I
believe that the human being is wholly responsible for his
own actions, I strongly object to this necessity and to the
morality that has spawned it. However, I would object even
more strongly to being sued-so here it is.
The price of man in motion is the occasional collision.
Motor racing is dangerous. In order to be competitive in this
business it is necessary to operate at the outer edges of the
performance envelope. The closer we come to the edge, the
greater the risk of falling off becomes. This book is about
improving the performance of the racing car and its driver-
particularly with respect to the roadholding department. It
deals with the deliberate exploration of the outer limits of
traction. The closer the racing car approaches its potential
in this department, the less forgiving it becomes and the
greater the chances of paying a sudden stop type penalty
become when an error in judgment occurs.
If, while attempting to apply any of the ideas, procedures
or advice contained in this book, you should come unstuck,
you will have done so through your own conscious decision. I
disclaim responsibility for your actions-and for your acci-
dent.
 CHAPTER ONE

VEHICLE DYNAMICS -
WHAT'S IT ALL ABOUT?

Before we can do anything intelligent with any piece of transmitted to the road surface through all four of the tires
machinery we had better figure out the exact function of the instead of through the driving wheels only. The vehicle's
piece-Hif all else fails, read directions." In the case of the ability to stop is relatively less important than its ability to
racing car that function is deceptively simple. The racing car accelerate because much less time is spent braking than is
exists onlv to allow one man to negotiate a certain fixed dis- spent accelerating. We stop faster than we accelerate.
tance in iess time than any other combination of man and
machine present on that day. Whether the distance happens
ACCELERATION OR CORNERING POWER
to be the 440 yards of a drag strip, 200 laps of Indianapolis,
14 laps of the Nurburgring or 1000 miles of Baja landscape Except for Drag Cars and Bonneville cars all race cars are
is immaterial. The racing car is not a technical exercise. It is required to go around corners. Obviously the faster that a
not an art object. THE RACING CAR IS SIMPLY A given car can go around the type of corners which it is called
TOOL FOR THE RACING DRIVER. Our objective in upon to negotiate, the less its lap time will be-for two
this book is to learn how to provide our driver with the most reasons. The first reason is simply that the faster the vehicle
effective tool possible within the framework of our is traveling the less time it will take to cover a given section
limitations-human, financial and temporal. of race track, either straight or curved. The second reason is
What this book is going to be about is Basic Vehicle equally obvious, although less understood. It is perhaps
Dynamics-a term that most people find somewhat frighten- more important. The car that exits a given corner at say
ing. The term dynamics brings to mind groups of confusing eighty miles per hour is going to get down the ensuing
diagrams accompanied by strings of obtuse formulae. It straight in less time than the car which exits the same corner
doesn't have to be that way. Vehicle Dynamics is simply the at seventy miles per hour. It will do so simply because it
study of the forces which affect wheeled vehicles in motion doesn't have to waste time accelerating from seventy to
and of the vehicle's responses, either natural or driver in- eighty miles per hour-it is already there and so has a head
duced, to those forces. In many cases it is sufficient to un- start. Factors which determine the cornering power of a
derstand the cause and effect of the forces and responses given race car include:
without establishing finite values or magnitudes. Since we
are interested only in the racing car we can and will ignore Cornering capacity of the tires, which is influenced by:
many aspects which concern the designers of passenger cars. Suspension geometry
For our purposes vehicle dynamics can be conveniently Vehicle load transfer characteristics
broken down into a few inter-related fields: Vehicle down force
Size and characteristics of the tires
LINEAR OR STRAIGHT LINE ACCELERATION Vehicle gross weight
Height of the vehicle center of gravity
The ability to accelerate faster than the next car is the
single most important factor in race car performance. It is
more important than cornering capacity and infinitely more TOP SPEED
important than top speed. Basic factors which govern the
vehicle's ability to accelerate include: In most forms of racing top speed is nowhere near so im-
Net power available at the driving wheels portant as it would appear to be. Unless the corners can be
Tractive capacity of the driving tires taken at top speed both cornering power and acceleration
Gross vehicle weight capacity are much more important. How often does the los-
Aerodynamic drag ing Drag Car come up with the highest trap speed? Elapsed
Rolling resistance time is the name of the game that we play-don't ever forget
Component Rotational Inertia it. Given the opportunity to gain significant engine torque
and area under the power curve in the engine's operating
range at the expense of peak horsepower-do it. When you
LINEAR DECELERATION find that your lap times are better with enough wing on the
OR BRAKING CAPACITY car to cut down the top end - don't worry about it.
Braking is simply acceleration turned around. It is Factors controlling top speed include:
governed by exactly the same factors as acceleration with Net power at the driving wheels
the power of the braking system substituted for net engine Aerodynamic drag
power. In this case the power of the braking system is Rolling resistance

9
 CONTROLLABILITY AND RESPONSE else is going to take an identical chassis, an identical engine,
an equal driver, a lot of hard work and a whole bunch of
If we could design and build a Can Am car with the
knowledge-tune on the whole package-and blow your
acceleration of a AA Fueler, the top end of a Bonneville Car
doors off. That's just about what tuning adds up to-the
and the braking and cornering power of a Formula One Car
difference between first and third.
it would avail us nought if it lacked adequate controllability
So in order to become competitive and in order to stay
and response characteristics. The racing car must be capable
competitive we're going to have to tune on the package. ~he
of being driven-and driven consistently hard-in traffic.
main reason has to do with the very nature of vehIcle
As you would expect, this is the difficult part. There are very
dynamics-there are so many comprom.ises and t~ade offs
few factors which do not affect controllability and response
involved that we can never realize the optimum possIble per-
but the most important are:
formance. Because the opposition can be depended upon to
Center of gravity height keep improving, we must also. Bu~ t~ere. is ano~he~ reason
Load transfer characteristics and this one involves the natural lImItatIOns buIlt Into any
Suspension geometry and alignment race car that you can buy.
Polar moment of inertia
Chassis and suspension link rigidity LIMITAnONS OF THE AS-BOUGHT RACE KAR
Differential characteristics
Slip angle versus coefficient of friction curves of the All race cars are full of design compromises. The bo~ght
tires "kit car" has more than the "works car." The obvIOUS
Aerodynamic balance reason is cost. The kit car manufacturer is vitally concer~ed
with his costs. He is engaged in one of the shakIest possIble
COMPROMISES AND TRADE OFFS business ventures and spends all of his time walking the thin
line between beans and bankruptcy. Even if he has brilliant
By now it should be becoming obvio~s that it .is just not concepts, he often can't build them be.cause ~e hasn't go.t ~he
possible to combine maximum acceleratIOn, ma~lmum cor- funds for new tooling and/or he IS terrIfied of prICIng
nering force, maximum top speed and optimum c?n- himself out of the market. Also he cannot afford to take a
troll ability and response characteristics in anyone vehIcle giant step forward that might not work-remember the Lola
You don't take a drag car to Indianapolis Motor Speedway HOD?
because it won't go around the corners. It won't go around That's part of the problem. Another part of it is the sim-
the corners because it was designed and developed for max- ple fact that most of the manufacturers do not race a works
imum acceleration. It has a very narrow track, a very long team of cars. The successful professional racing teams don't
wheelbase and an enormous concentration of weight on the build customer cars because it is a pain in the ass, it doesn't
rear wheels. It has tiny front tires and no suspension. It just make very much money and it inevitably dilutes the racing
doesn't want to know about corners-but it surely does effort. The kit car manufacturers don't race because they
accelerate. By the same token, A.J. had best not bring his can't afford to. Since they can't sell very many cars without
Coyote to Irwindale. Even if it had enough power it w?n't racing successes to boast about they usually give some sort
transfer enough weight to the rear wheels, the fat front tIres of support to carefully chosen raci~g te?ms in t~e hope ~hat
will slow it down, etc., etc. This much is pretty obvious. these "works supported" teams wIll Win and, In so dOIng,
What is not so obvious is that the same type of trade off and create a demand for the product. The team does all of the
compromise affects the performance of every racing car on testing and development and supposedly passes the word on
the circuits that it was designed for. If we can gain corner to the factory for the ultimate benefit of t~e custome.r. Good
exit acceleration at the expense of corner apex speed-or Luck! The race team is guaranteed to dIsplay consIderable
maybe vice-versa-we may be able to improve our lap time. reluctance at passing on their hard won tweaks for the im-
Or if we can gain corner apex speed at the expense of top mediate benefit of the opposition. What does trickle down
end-or whatever. Just to make things a little more complex does so just as slowly as the racers can arrange it.
we must also realize that the optimum set up for a given car Further, at some cut off date before work is actually
at Long Beach, with its predominance of slow corners, is go- begun on a batch of customer. cars, the desi~n must be
ing to be less than brilliant at Mosport where the co:ners ?re frozen or they will never get bUIlt. After that tIme the best
very fast indeed. Add to this the fact that no two drIvers lIke you can hope for is the opportunity to buy expensive update
their cars set up exactly the same and the hope that our kits.
knowledge of vehicle dynamics is constantly growing, and The last bit has to do with operating conditions, tire
we begin to understand why this is not a simple business. characteristics and driver skill. Development may well have
There is a school of thought, particularly prevalent been done on circuits totally different to those that you will
among those new to racing, that the way to ensur7success is race on and/or with tires of dif~erent charac~eristics. It m~y
to purchase whatever chassi.s is winning, bo~t In the best also have been done by a certIfied hero drIver whose skIll
engine that money can buy, Install a super-drIver and start and experience requires a much less forgiving car than your
collecting first place checks. WRONG! rookie driver is ready for.
Assuming that enough spares, support equipment and
competent mechanics are included in the package and that a
TUNING
good manager is around to make the decisions and run the
operation, this is a good way to consistently finish third or Anyway, what you can buy is a starting point. In a really
fourth. But it will not win. It will not win because someone competitive class of racing it is unlikely to be capable of

IO
winning races out of the box. Development is up to you. You have freedom of rotation about all three of their axes-roll
will do it by tuning. pitch and yaw. Except when leaving or returning to the earth:
My definition of tuning is simply any intentional t~ey ar~ free of ground effects. Normally a pilot finding
modification to any component of the total race car system himself In trouble near the ground has the savmg option of
made for the purpose of increasing the probability of win- going up. At those times when this option is not available
ning a motor race. The removal of unnecessary weight is both the pilot and the designer are a lot more interested in
tuning. So is increasing effective power output, improving stability than absolute performance so that the aircraft will
cornering power, reducing drag and just about anything else be operating well inside the limits of its performance
that we can do to our machines to make them faster, more envelope. Crop Dusters, Fire Fighters and Close Ground
controllable or more reliable-although reliability has more Support Pilots, forgive me-your game doesn't count in this
to do with preparation than it does with tuning. discussion.
In extremis, if the aircraft designer, builder, tuner or pilot
WHAT'S HAPPENING OUT THERE has really screwed up, the driver of the high performance air-
craft normally has one final option-he can jump out of the
Since the publication of PREPARE TO WIN I have thing. This becomes rather more difficult in the case of the
received many ego inflating comments. To date no one has racing driver and, with the notable exception of Masten
disagreed or even found fault with any of the factual
Gregory, has seldom been attempted with success. Even
material, procedures or recommendations put forth. This
Masten got tired of it after while.
will not be true this time! The actual preparation of a race
Among high performance machines the racing car is a
car, an aircraft or a machine tool is merely the compilation rather unique projectile. It operates ON one medium-the
and sorting out of what has been learned by those who have
earth-and IN another medium-the air. It receives
operated similar equipment under like conditions. Ex-
simultaneous, and sometimes conflicting, inputs from each.
perience and judgment is necessary but the field is pretty
It has only two dimensional freedom of rotation, and even
much a black and white area. Someone, somewhere, can
that is severely limited. While full rotation about the yaw
answer correctly-virtually any question that comes up.
axis is not uncommon it is also not desired. Nothing good
None of the above is true of tuning-at least of tuning on has ever been reported about the full rotation of a race car
the racing car or virtually any part thereof. Tuning is like about either its pitch or roll axis. The machine operates in
designing in that, if it were a precise science, all of the cars tenuous contact with the earth while passing through the air
campaigned by competent organizations would exhibit no with instantaneously varying values of velocity, yaw and
faults or vices, drivers would have nothing to bitch about, pitch. It is forever being upset by inputs from the ground,
every modification and demon tweak would work and the the air and the driver.
cars would go like stink all of the time. None of this The driver has control of three thrust inputs to the ground
happens. We spend most of our professional lives in one -acceleration, deceleration and turning-but only up to the
quandary after another-wondering why our bright ideas limit of tire traction in each case. After that the immutable
don't work-and searching for our very own Holy Grail. laws of physics take over and, while the behavior of the vehi-
Once in a while we make a breakthrough and think that we cle can be modified to some extent after that point has been
have gained a tenuous hold on the handle of the grail. reached, the laws are indeed immutable. The driver has no
Inevitably we then find that whatever bit of knowledge we control over the inputs received from either the ground or
have just learned merely lets in enough light to allow us to the air. He must anticipate and/or react to these inputs with
see a whole new series of problems. The visibility at the best control responses in order to prevent disaster. He has no
of times is liable to be a bit hazy due to clouds of ignorance. direct aerodynamic control over his vehicle. Just to make
The basic problem, as usual, is very simple. We just don't sure that he doesn't become bored, if he is going fast enough
know enough about what we are doing. to be competitive, he will constantly combine turning with
This is not to imply that racers are stupid, or ignorant or either acceleration or deceleration-all of them at the limit
lazy. To the contrary-a more clued-in and dedicated group of adhesion and in very close proximity to other vehicles. "If
of individuals has never trod the earth. For reasons having to you have complete control over the damned thing, you're not
do with "the lacks" -lack of money, lack of time and lack going fast enough."
of communication-NO ONE has yet defined in detail just For some years now it has been technically feasible to
what is happening, in the vehicle dynamics sense, as the rac- quantitate much of what is actually happening in various
ing car is driven around the race track at high force levels. areas as the race car is hurled around. Jim Hall pioneered
How can this be? After all, high performance aircraft are the field. Ford did some instrumentation work during the
much more complex than race cars, they operate at vastly late lamented Le Mans program. Donahue and Penske did a
higher speeds and they are defying the law of gravity to start lot more, and now Ferrari, McLaren and Tyrell are well
with. They have nonetheless been developed to a rare state of into it. I doubt that it is entirely coincidental that each of
perfection and, with minor but exciting exceptions, can pret- these operations has won more than its statistical fair share
ty much be depended upon to operate to design objectives of races.
straight off the drawing board and out of the wind tunnel. Having quantitated what is actually happening as op-
Why have we failed to achieve this level with our relatively posed to what the engineers think should happen and what
simple devices? the driver feels is happening, it should then be possible to
There are several reasons. Physically, the foremost is that study the accumulated data and, by modifying hardware,
aircraft operate in one medium only-the air-and they change the vehicle's dynamic responses in the direction of

II
I
 optimum performance. To my knowledge no one has yet -and that IS a normal winning margin.
gone all the way with instrumentation evaluation programs. The biggest single mistake that racers make is in looking
There are no governments and precious few giant cor- for the super tweak that will produce one large chunk of lap
porations in motor racing, and the finances required for time. Assuming that the equipment is both good and sorted
such a program are beyond the resources of individual race out, that tweak does not exist.
teams. We are not going to concern ourselves with extensive In the days when we still had a Formula 5000 series-
instrumentation as it is very unlikely that the reader will before an inexplicable wave of insanity passed through
have access to it. Denver-the reason that Mario Andretti was two seconds
This is not necessarily all bad. Motor racing, so far, faster than the second place qualifier-and four or five
remains a field where the informed improviser-the try it seconds faster than the tenth place qualifier-was not
and see tuner-will usually beat the conventional engineer. because of his engine, or his tires or his basic chassis was
This is simply because the conventional engineer will be re- that much faster. It wasn't because his driving skill was that
quired to operate in the absence of many of the inputs with superior-although, in this case, I must admit that driving
which he has been trained to work. He will also usually un- skill was a larger than normal part of the picture - I'm a
derestimate the importance of the driver in the performance Mario admirer. The real difference was in the accumulation
equation and over estimate the importance of aerodynamic of a lot of tiny little increments of lap time-a tenth here and
drag. In this over organized world there are too few a hundredth there painfully gained through endless hours of
technical endeavors where the maverick can succeed. Motor testing and tuning. Once the car is basically sorted out that's
Racing, if the maverick thinks clearly enough and works all you are going to gain by tuning-tenths and hundredths.
hard enough, remains one of them. It's enough.
So what do we tune on-and how do we decide in which In the chapters that follow I intend to explore the more
direction and in what order to proceed? That's why it is an critical areas of vehicle dynamics as they relate to the rac-
art rather than a science. We tune on just about everything ing car. I will attempt to do so in logical and simple fashion,
from the driver's head (usually the most productive, but out- utilizing a minimum of mathematics and formulae. The
side the scope of this book) through the tread pattern of the book is not meant to be a design manual; nor is it intended
rain tires to the power output of the engine (usually the least to be a "follow me book" which tells the reader in several
productive). Hopefully we will do so from the firm base of thousand words that if he reduces the diameter of the front
as broad an understanding of vehicle dynamics as we can sway bar he will reduce understeer. Rather it is intended to
muster. We will do it in logical fashion and we will prioritize say, "this is the way it works and these are the options by
our efforts so as to gain the most amount of performance means of which we can modify its behavior-in this direc-
per dollar spent and per hour invested. For certain we will tion."
proceed one step at a time. Equally for certain we will We will discuss the various forces that affect the racing
attempt to avoid the common human tendency to get all car and the vehicle's responses to those forces. Then we will
hung up on one particular area-be it aerodynamics, un- get into the specifics of how to tailor or modify the
sprung weight, track width or whatever. The racing car is a responses by tuning. We will not discuss Drag Cars because
system and each component of the system contributes the I know nothing about them. We will basically be concerned
performance of the whole-although not equally so. More to with Road Racing Cars although virtually everything will
the point, each area of performance interacts with all other also apply to Circle Track Cars at least on paved tracks. I
areas, and it is necessary to view the effect of a given change also know nothing about Dirt Tracks or about Off-Road
on total performance. If this principle is engraved firmly on Racing. It is, however, my firm conviction that these areas
our minds we may achieve maximum success with minimum are also subject to the laws of vehicle dynamics and that
grief. If we allow ourselves to lose track of it success may much of the material which follows must be applicable-....
still come our way-but only by chance. with modification to suit the operating conditions. The prin-
ciples involved remain constant, but we must weigh our
SMALL INCREMENTS OF LAP TIME
applications of them in the light of expected conditions.
N ow is perhaps the time to speak of the importance of Science always lives. It is only our interpretation and
tiny increments of lap time. Every racer is willing to admit application of science that gets a little shaky.
that one second of lap time is both a real and a significant By definition the racing car spends all of its real time flirt-
interval. Indeed any real racer will sell his mother and rent ing with the edge of tire adhesion. If it is not doing so then
out his lady to gain an improvement of one clear second per either it is momentarily on a part of the circuit where adhe-
lap. After all, one second per lap at Riverside is forty sion is not a factor (i.e. on a straight long enough that
seconds at the end of the race-and when was the last time available torque is not sufficient to upset the car) or it is not
that anyone won Riverside by forty seconds? Now try to being driven hard enough. This being the case we had better
convince this same racer that one tenth of a second has start with a look at the factors which influence and govern
significance. I'm going to let you in on a secret! One tenth of that adhesion. We are not and will not be interested in the
a second per lap is four seconds at the end of a forty lap race lower eighty-five percent of the performance envelope.

12