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1

How Does the Driver Controlthe Car?

(Introduction to the article in the “Technical

Pages”.) 

The Driver and Car Handling - accelerating,braking and cornering.

From a control point o view, cornering is themost demanding and interesting or analysis.

 ! new perspective.

Dale Thompson

"acing Car Technology

www.racing-car-technology.com.auino#racing-car-technology.com.au

$ote% &n vehicle dynamics terminology, cornering or turningo the vehicle is reerred to as 'yaw( or 'yawing( o thevehicle.

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)

 The Weight Transfer Worksheet &n this web site, we recommend to you our spreadsheet calculations, the

"acing Car Technology *eight Transer *orksheet +*T*. *eight transerconsiderations are now common in procedures or suspension tuning.*orking with race cars over a number o years, we have shown the *T*can give good results. The *T* remains the only ully tested, ullydocumented weight transer 'calculator(, that anyone can use.

ut it does not represent how the car works. ome will say at this point,'How else could it work/( The predominant view amongst the racing and

perormance car community is that handling and control must be about theweight transer and chassis roll.  !t universities all around the world, engineers are now taught the 'single

track model(. The ociety o !utomotive 0ngineers have mandated a wholerat o standards and conventions that allow vehicle dynamics engineers totalk the same language.

sing the ideas, we can gain a truer understanding o oversteer and

understeer. *e highlight how the driver controls the car.    Of the TV show “Top Gear”, How can The Stig drive really,

really Fast? This video explains or ideas in generalter!s" See www"yot#e"co!$racingcartech"

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2

Driver “Feel” for the Car 

The interaction between the driver and racing car, his eel or the car, is

described by 3ichael chumacher +circa 1445, 

67ou have to have the senses in your whole body, that come up to yourbrain, and then, in the end, you have to transer the inormation tothe steering wheel. &t is how you do this that is the dierence

between drivers, between those who are sensitive, who have moreeeling, and those who may be as sensitive but are not able totranser that into their driving.'

He e8presses a level o uncertainty about whether it is the eeling, orwhat you do with it, that counts.

*hat it is the driver is sensing/ How does the driver control the car/*e9ll start with what happens to the car in a corner. +The ollowingdiagrams are based on the 'single track model(

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:

Cornering – Very Slow 

%ofG

&nst" 'ir"

Travel

Vehicle

path

Vehicle

%$( 

&nstantaneos Trn

%entre

β

)

;ery slow turning, no 'slip

angles( at the tyres. The

curved path o the Co< is

shown. &nstantaneousdirection o travel is at right

angles to turn radius, ".

β is the “attitde angle”

%ar is pointing ot fro! the

trn"

Copyright C "acing Car Technology )==>

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@

Cornering – %versteer a tighter#ath&$

%ofG

&nst" 'ir"

Travel

&ntended

Vehicle *ath

Vehicle

%$( 

&nstantaneos Trn

%entre

β

)

& slip angles increase at the

rear, aster than the ront, the car

will rotate urther in the direction

o the turn, increasing theattitude angle,

β

. The turn

radius, " will shorten as shown.

The vehicle will steer a tighter

path, as shown.

 

Oversteer

Vehicle *ath

Copyright C "acing Car Technology )==>+ote The rear tyres

are not sliding

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>

Cornering – 'n"ersteer a wi"er#ath$&

%ofG

&nst" 'ir"

Travel

&ntended

Vehicle

path

Vehicle

%$( 

&nstantaneos Trn

%entre

β)

 

-ndersteer

Vehicle *ath

& slip angles increase at the

ront, aster than the rear, the

car will rotate out o the turn,

reducing the attitude angle.

Turn radius, " is lengthened,

as shown. The vehicle will

steer a wider path as shown.

Copyright C "acing Car Technology )==>+ote The front tyres

are not sliding"

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A

 (ttitu"e (ngle at the Centre of)ravity 

 

Front axle attitde angle

)ear axle attitde angle

.ttitde .ngle

.ttitde angle, the angle #etween vehicle centre line and direction of travel, is

also /nown as “float angle”, “#ody slip angle”, “#eta angle”" &t is a fnction of

the front and rear slip angles, as shown in previos diagra!s"

The attitde angle varies at different points along the centre line of the car" For

or prposes, we consider it at the centre of gravity" &n the next slide we

de!onstrate how n#alanced lateral forces at the front and rear tyres will case a

change in attitde angle, and ths #e an instant indicator to the driver of the

ndersteer$oversteer #alance of the car"

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4

*alan+e" or un,alan+e"lateral for+es at the tyres$

 

.ttitde .ngle

 For netral steer, FF x a 0 F) x #, ie the rotational forces are

#alanced" FF x a 1 F) x #, the car is in oversteer 2 increasing attitdeangle" FF x a 3 F) x #, the car is in ndersteer 2 decreasing attitde

angle"

&t is clear fro! the previos slides that the car is not rotating arond

the %G" The trn centre is !oving and trn radis is lengthening and

shortening"

Front

# a

F)

%G

FF

4o!ents arond the centre of

gravity will leave s with a net

rotational force arond the %G"

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1=

%versteer an" 'n"ersteer   3a8imising grip at all our tyres is the initial aim. o tyre

selection, temps, pressures, cambers, toe etc are oprime importantance. ut because o the transientnature o handling, +corner entry, mid corner, e8it, it alsoworks out we also ma8imise overall grip with attention tospring reBuency - springs, !"9s and shocks controlling

ride, roll pitch rate. ut suspension tuners also have to be able to balance

the car or oversteerundersteer - grip o the ront wheelpair versus grip o the rear wheel pair as per previous

slides. &deally we look to 'stick the loose end( so as toincrease overall grip. ometimes that cannot be done.o or e8ample, we might choose a compromise balancethat optimises corner e8it acceleration at the e8pense osome mid corner grip.

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 What-s ahea" in the Te+hni+al.ages?

The article urther e8plores the notion o the attitude angle being theprimary source o eedback to the driver. The driver can eel thechange in attitude o the car, over and above the e8pected attitudeangle generated by the vehicle when in neutral steer. The driver ise8tremely sensitive to the car balance, but largely unaware ooverall grip. ut give himher a little e8tra grip and he will use it and

go aster, while reporting the car unchanged.  !lthough a very intuitive concept or drivers, it remains largely

ignored by mainstream suspension tuners and race engineers. Thismay be because o the diiculty o constructing a reasonable, easyto understand model. y taking a new perspective on understeerand oversteer, as per the diagrams in this intro, we oer a model

that can predict and e8plain the motion o the car. To get the ull article, please subscribe on the ront page o our web

site. ?r contact me direct about subscribing without using aypal, iyou preer. ino#racing-car-technology.com.au