Race Seminar

Race Car Engineering

Good Handling is

• Grip

=

tires operating at maximum

adhesion to the track surface.

• Balance

=

both ends of the car are

operating harmoniously, the car instills

confidence and is fun to drive.

• Control

=

the car responds quickly and

predictably to driver inputs, you can make

the car do what you want it to do.

Grip

• Those factors which influence the adhesion of

the tire to the track

– Tire Temperature – Tire pressure

– Camber

– Tire loading -- Balance – Tire Compound

– Tire performance

Balance

• Weight transfer

• Relative Front and Rear Slip Angles

• Car rotation

• Consistency in fast and slow corners

• Transitions

Control

• Steering response

• Stability

• Transition

• Responsiveness

• Progressiveness

Axiom 1

If you want to corner at 2 G’s you have to

support the car for 2 G’s forces.

Regardless of the individual setups, two

similar cars cornering at the same speed

Outline

• Notes on chassis alignment & Record keeping

• Grip = Tires: Slip angle and Grip

• Balance = Suspension Geometry Static Analysis

= Suspension Dynamics &Weight Transfer

• Control = Chassis tuning – without shocks

= Chassis tuning – bump rubbers and

droop limiting

= Shocks

Myths

• Fix the end that has the problems first

• If a car pushes soften the front springs or ARB

• If a car is loose soften the rear

• More rebound will make a tire grip better

• Anti Roll Bars increase weight transfer

• There are soft setups and there are hard setups

• Increasing spring rates will make the car hard to

drive

• Just get out and drive or a different line will solve

the problem

Facts

• Get the car balanced FIRST.

• Push or Loose, under-steer or over-steer are

balance problems.

• An unbalanced car is a car that is

underutilizing the tires a one end and over

utilizing the tires at the other end.

• Setups must be tuned to the prevailing

conditions.

•Most drivers can not tell the difference between an

improvement in control and an improvement in grip

•A car is supported during cornering through the

combination of Springs, ARBS, Shocks, and

Dynamic Suspension Geometry.

•The line a car takes through a corner is more

dependent on the car setup than the driver’s

technique.

•Consistently fast cars are easy to drive.

•

Good Setups are the product of hard

work done in a systematic manner over

time.

•

Good record keeping of setups, details

of each session on the track, and a

record of all changes will tell you what

you did to make the car fast and help

you correct the car when it is not fast.

Accuracy

How accurate do

you

Chassis Setups

require

• Accuracy:

2001 SCCA Runoffs percentage that 10th _qualifier

was behind pole FV 1.4%, FF 1.2%, FM 3.5%, FC 1.5%, SRF 1.2% An acceptable tolerance should be no more than half the qualifying difference, 0.6%

• Repeatability:

Same degree of accuracy, 0.6%

• Ease of operation:

If it is too hard or cumbersome you will not maintain the accuracy through out an event. The system must be portable.

You should do your work with a degree

of accuracy that this race was decided.

Equipment You Make

• Ride Height Gauge

• Bump Steer Gauge

• Alignment Flags

• Toe Bars and trammel bars

• Trammel Pins

Bump Steer

Gauge

Plate mounts to spindle

As the upright is raised or lowered any change in toe causes the plate to twist relative to the indicators. The indicators rest against the plate and move in or out as the plate is moved.

Indicators

Base Plate

Should be heavy.

This tool is accurate within a few thousandths of an inch.

Ride Height Gauge

Trammel Pin

Procedures - Sequence

• Set ride height

• Zero toe settings

• Adjust camber

• Adjust caster

• Zero toe settings and take new readings

• Repeat the process until correct

Use to set Camber, Toe, Ride Height

Flag Alignment System

1.5 Square Tubing

Plate Measure the gap

Alignment Notes

• Do setups without driver but with

representative fuel load.

• Check the setup before and after running the

car.

• Have an alignment process for home and a

checking procedure for the track.

Setup Work

Sheet

This is an example of a work sheet for recording the settings as you progress through the

For Those Who are Prepared

• Record the lengths of all suspension arms:

a-arm legs, toe links, radius rods, push rods,

etc.

• Keep records of all changes to any of these

measurements.

• Have these records available at the track in

case a suspension arm needs to be replaced

Suspension

Build Sheet

The idea is to keep good and accurate records of the setup

Chassis Data

Sheet

This Sheet contains information to help make quick and accurate

Corner Weight and Ride Height

Once on the alignment pad proceed by:

• Resetting ride height

– Front ride should be equal side to side – Rear ride should average the target

• Setting corner weights

– Front weight should be equal

– Remember that weight moves diagonally across the chassis

• Alternatively set the front weights even while

keeping the chassis level (two scale system).

• Repeat the process until weights and ride heights

are equal with any discrepancy taken at the rear

The Set Up Sheet should contain all the necessary information to reproduce the exact settings.

Additionally, the set up sheet can contain any additional information to give a better understanding of the particular setup.

Set Up Sheet

The Run Sheet is the record of all the on-track activity. Additionally it may show the starting set up as a reference to help decide what changes are appropriate.

When the session is over, the Run Sheet gives a complete record, showing the beginning, all

intermediate steps, and the ending setup.

The Run Sheet is the record of the performance for any given setup.

This is an example of the run sheet

This sheet shows where the setup was at the beginning of lap 80.

It shows the lap times for each outing, the amount of fuel, the drivers comments for that outing, and the setup changes that were in effect for that outing.

This is the formal and necessary review of the time on the track.

Combined with the chassis set down sheet, this sheet is guide to the future changes in the set up.

This is the most neglected aspect of record keeping. The driver always has more pressing things to attend to such as girls and glory. This sheet when properly executed is the best key to a better setup.

An alternative form of the driver Debrief Sheet

Using a map to make notes on is easier and sometimes more helpful. It is also easier to leave out important details. Make a check list to be sure that all details of the debrief are covered

Chassis

Set Down

/

Set Up

The sheet records the ending set up and well as provides space to record changes for the next session.

Gearing:

How to select gears

1. Determine the lowest speed at which you can apply full power. This speed should correspond to maximum torque in first gear.

2. Determine the maximum speed any where on the course. Be sure to allow for drafting other cars and wind direction. 3. Choose the intermediate gears so that the RPM drop

between successive gears is constant or declines slightly as speed increases.

4. When going up hill keep RPM higher and avoid shifting. When going down hill use lower RPM by shifting sooner or gear longer.

Gear Ratios

This Sheet presents both graphic and analytical tools for analysis ratio selections. The right hand (shaded) portion of the charts shows critical speeds and the RPM for that speed in each gear. The graph is a way of

viewing the RPM drop for each gear change.

The top chart has the ratios from the Setup Sheet.

The lower chart is used as a work sheet to try alternative ratios.

Tires: Slip Angle

How does a tire develop GRIP?

Tire

Track Surface

Grip is the result of:

•The inter locking of the tire and track •Adhesion of the tire to the track

•Tearing force required to separate the

tread material from the tire.

Medium Grip

High Grip

It takes time and pressure for

Lateral Force vs. Slip Angle for given Normal Loads

Avon Tires

Front Tires Rear Tires

150 kg = 331 lbs

250 kg = 551 lbs

It is all about Grip

Sustainable lateral force

More grip is lost by unloading the inside tires

than is gained by increasing the load on the

outside tires.

Less weight transfer will result in greater total

cornering force.

Things to Increase Grip:

• Press the tire into the track surface

harder.

• Increase the time the tire has to conform

to the track surface.

• Increase adhesion between the tire and

Slick Zone of Tire Temps.

• Lateral force due to friction between tire and track

• Lateral force due to adhesion of the tire to the track

• Combined lateral force generated by the tire and track.

30 50 70 90 110 130 150 170 190 210 230

Decrease in total grip

The decrease in friction is due to the decline in the rigidity of the tread compound as the compound warms and before the tires begin sticking to the track.

1. There is no cornering without lateral force

2. Lateral force produces weight transfer

3. Lateral force plus weight transfer produces Slip Angle

Therefore

Handling is about Weight Transfer and Slip Angles

Axiom 2

Contact Patch Distortion Tire Foot Print

Steering: no slip angle

Balanced or neutral cornering Slip angles are equal

Steering is Full Ackerman Geometry

Instantaneous

Cornering: 5 deg. Slip angle

Outside tires have equal Slip angles. Thus neutral or balanced handling

Cornering: 8 deg. Slip angle

The steering angle of the front

wheels is nearly constant for all the slip angle conditions (decreasing less than a degree).

Cornering: combined illustrations

This is the path of the instantaneous center of rotation given a constant radius and varying slip angle for the outside tires.

This illustrates a balanced cornering condition.

0 degrees

5 degrees

Under Steer vs. Over Steer

• As you increase your speed through a

corner the steering angle should remain

constant regardless of corner speed.

• An under-steering car requires ever greater

steering lock with speed.

• An over-steering car requires less steering

lock with speed.

Under Steer

: unequal Slip Angles

Rear Slip Angle 5 degrees

Front Slip Angle 8 degrees

Center of Rotation Front Tires

Center of Rotation Rear Tires and the car as a whole

Over Steer

: unequal Slip Angles

Rear Slip Angle 8 Degrees

Front Slip Angle 5 Degrees

Center of Rotation Front Wheels

Center of Rotation Rear Wheels

Notice the tire distortion. The front tires are turned to balance the front and rear slip angles and adjust the corner radius. The car is tracking around the corner.

There is

no

cornering force

without

Slip Angle.

Toe Settings

and

Camber Angles

preload

the

Slip Angle.

Friction Circle

• Ft max = maximum G of about 1.25 acceleration and 1.25

cornering.

-2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 Lateral G’s Left Turn

2.5 2.0 1.5 1.0 0.5 -0.5 -1.0 -1.5 -2.0 -2.5

Lateral G’s Right Turn Acceleration

Braking

Ft max

-1.75 -1.25 -0.75 -0.25 0.0 0.75 1.25 1.75 2.25

Camber Shifts the Circle, increasing the cornering in one direction and decreasing in the other. Camber to left 2.5 2.0 1.5 1.0 0.5

Friction Circle and the

Combined G Graph

Speed

Combined Gs

Mid Ohio Note: Slower and earlier entry to the corner

along with the higher minimum and higher exit speed.

Better utilization of the car’s potential

Friction Circle and combined G’s

Speed

Combined G’s

Throttle

Note: the early setup and power application

Combined G’s again

Speed Combined G’s Brake Pressure Steering Throttle

Note constant speed period and drop in combined G’s as the driver floats

Tire management and understanding

what they are telling you

New tires care and feeding

Inflation prior to being used.

Set pressure as soon as possible after mounting.

Inflate to stretch undersize tires.

Use a tire record sheet - track miles, position,cycles.

Direction of rotation.

Temperature across the tire. Temperatures front

to rear. Tire pressure rise is more accurate

indication of car balance.

How to maximize tire life

Determine the balance of a car before the tires

are damaged. Rotate tires after a predetermined

number of laps. Dismount and reverse on the

rim.

Recommended number of wheels - 14 - to

reduce tire costs

Getting the tire pressure correct is vital to good

performance and life. Always use the same gauge.

Set pressure of all tires in the morning. Record all

changes in tire pressures. Use the record of tire

pressure adjustments to adjust new sets.

Tire pyrometer use

Where to stick the needle. Consistency is vital.

Measure quickly after a run.

Tire Record

If you have a tire

Steering

Geometry:

Balance &

Suspension Geometry: Steering

• Camber

• King Pin Inclination (KPI) also called

Steering Axis Inclination

• Scrub Radius

• Caster

• Caster Trail

• Toe

Steering Axis

King Pin Inclination

King Pin Axis

Camber Angle

Steering Axis

Caster

Front

Caster Trail

Steering Axis

Side View

Steering Axis

Scrub Radius

KP Axis at ground

Steering Trail Steering offset

Pressure Center

Front

Steering Axis

Front

Steering Axis: So What ?

• Caster causes the front wheels to lean in the

direction of the turn.

Caster and Steering Axis

Tire Contact Point

Plane of

Steering Axis

Pure caster causes

the tire to lean in

the direction

of the turn.

King Pin Inclination (KPI)

Steering Axis

Ground

KPI

– Pure, no

Caster

Steering Axis

Spindle

Steering Plane

Ground

KPI + Caster

Scrub radius causes longitudinal

forces at the contact patch to

generate torque about the steering

axis.

Caster combined with trail causes

steer dive when the wheels are

•Caster combined with scrub radius causes the car to drop as a wheel steers in toward the center and

causes the car to rise when a wheel steers outward.

This in turn causes a weight transfer from the outside front – inside rear diagonal to the inside front -

outside rear.

•King Pin Inclination (Steering Axis) causes both wheels to gain positive camber as they are steered away from center.

•King Pin Inclination causes steering lift as the wheels are steered from center causing a self centering

torque.

Steering Axis 2

•Steering Axis may be offset rearward from the wheel

center to reduce Caster Trail and thus reduce the steering effort.

Steering Axis Offset

Lola T97 Indy Lights

Example

Steering is straight Roll angle

Suspension displacement is taken from the damper

displacement data.

Suspension as in turn 1 MO 2.5 G’s lateral acceleration

.227 deg

Roll was .227 Now .417 with steering input

Roll Center was 1.366 to the right Now it is 3.594 left

As the car is steered the inside front suspension rises and the outside front falls

Full Ackerman

Steering Geometry

All wheels steer about a common point

The inside front is turned sharper because it must turn about a shorter radius.

Any other geometry results in the a front tire skidding as the vehicle turns

Example: corner push with

exit snap over steer

• Driver says “entry all right, mid corner mild under

steer, but corner exit the rear steps out”.

• Tire temperatures are normal or front tires are

cooler than the rear. Tire pressure rise for front

tires is same or less than the rear.

• Problem is that the car is under steering. But at

the exit, as the steering wheel is straightened, the

grip on the outside front tire increases causing the

front to turn more in the direction that the front

wheels are headed. Result the rear steps out.

Why does the grip increase?

• As the steering angle is reduced the slip angle is reduced and it

approaches the optimum for the load on the front tire. Thus the grip increases causing the tire to follow more closely the direction the wheel is turned. Refer to the carpet plots of slip angles and forces. • The inside front tire increases grip because the lower slip angle and

increased load.

• The load on the outside front tire increases as the steering is

straightened because of the effect of the steering geometry. The inside front tire drops (ride height increases) as the outside front tire rises (ride height decreases). This is the result of the combined action of KPI and Caster.

• Other symptoms:

– Front tire temperatures lower than rear

– High wear of inside edge of outside front tire

• Cure:

– Stiffer front end more ARB or Front Spring – sticks the tire into the ground

– Stiffer rear spring, not more rear rear ARB – increases the rear slip angle relative to the front

– Higher rear ride height – more rear slip angle

Under Steer 1

• An under-steering car is slow to respond.

– Therefore you must start your turn in early in order to make the apex. You can not drive the fast line with an under-steering car.

• Most drivers feel comfortable with some amount

of under steer because their experience of over

steer is the corner exit snap out type,

unstable.

• When a car is neutral, the steering angle is

constant for a given radius turn even as the speed

and slip angle in the turn increases.

• Alternatively: the steering angle of a neutral car

changes as the turn radius changes.

More about Camber

• Camber causes an uneven distribution of pressure on the contact patch.

– The inner edge of the tire is compressed more than the outer edge.

– The tire is composed of two springs (the side walls) supporting the contact patch (tread).

• The uneven pressure results in a

lateral force, Thrust, in the direction of the camber.

• The thrust preloads the slip angle causing lateral stability.

• Camber increases grip by increasing the load on the inner edge of the tire. • Camber Shifts the friction Circle right

thus increasing lateral grip.

More about Toe

• Toe preloads the Slip Angle. • Slip angle creates lateral grip

and lateral thrust.

• Slip angle increases lateral stability.

• Front toe out counteracts front camber thrust.

• Rear toe out can help corner transitions.

• On a driven wheel toe increases rolling resistance.

• On a drive wheel toe has little effect.

Front Toe in

Chassis

Balance

Chassis

Dynamics

6 Degrees of Freedom

Movement Along the three axis's

Longitudinal axis – Acceleration & Deceleration

Lateral axis – Lateral Acceleration or Turning

Vertical axis – Change in ride height

Rotation about the three axis

Roll about the longitudinal axis

Pitch about the lateral axis

Yaw about the vertical axis

A vehicle suspension system controls the movements

of the vehicle in all three axis’s, restraining the six

degrees of freedom.

Controlling Chassis Dynamic Movement

is the key to a

Balanced Setup.

• Controlling weight transfer,

• Controlling slip angle development

.

Suspension Geometry, Springing and Damping

are the main mechanisms to achieve balance

.

Suspension Kinematics 1

• Instantaneous Center

– The instantaneous point about which an individual wheel rotates in bump (vertically).

• Roll Center

– The roll center is the intersection of the two lines formed between the tire contact patch and their respective instantaneous centers.

– It is possible for the roll center to be outside the track of the car.

• Mean Roll Center Height

– The point about which the body rolls.

– The Mean Roll Center starts on the vertical center line of the chassis and at the same height as the Roll Center and can shift within the width of the track.

Suspension Kinematics is the movement of the wheels as constrained by the suspension geometry.

Shown is a Single Wheel

Instantaneous Center

Front View Swing Arm (FVSA)

Roll Center

• The roll center is the point through which tire forces act on the sprung mass of the car

• Rollover moment arm is the distance from the Center of Gravity to the Roll Center.

• Roll resistance arm is the distance from the center of the chassis to the pressure center of the tire at ground level because the springs and anti roll bars act at the tire pressure center. Shifts with the mean roll center. • Jacking is the vertical component of the reaction forces of the tire

pressure center to the roll center.

Weight Transfer

: first look

Weight transfer is a function of; Mass

Center of Gravity Location Wheel Base

Track

and the Forces Acting on the Mass

Springs, anti Roll Bars, and Shocks determine the

rate and distribution at which the

loads change on the four corners of the car.

Lbs. transferred = ( lateral G’s) x (mass) x (c.g. height) (wheel base or track)

Suspension Dynamics

•Pull the handle slowly and the glass will move across the table. •Pull the glass faster and the glass will fall over.

Suspension Dynamics

Stationary

Pull

Un-sprung Mass Weight Transfer

CG

Pull

CG

Lateral Acceleration

Reactive Force / Grip

Stationary

Weight Transfer

Weight Transfer

Sprung Mass

Pull

Sprung Mass weight transfer

with Springs

R/C

Pull Lateral Force

Traction Force acts through the R/C

Un-sprung Mass Weight Transfer

Geometric Weight Transfer

Jacking Force

Geometric Weight Transfer

Jacking Force

R/C

Traction Force acts through the R/C

Traction/Grip Forces exert a horizontal and a vertical force. The vertical component is the jacking force.

Pull Un-sprung Mass Weight Transfer Sprung Mass Geometric Mass Lateral Force

Lateral Weight Transfer

• Un-sprung Weight Transfer = (un-sprung mass * Lateral Acceleration * non-suspended mass Cg height ) / Track

• Geometric Weight Transfer = ( Sprung mass * Lateral Acceleration * Roll Center Height) / Track

• Sprung Mass Weight Transfer = (Sprung mass * (Sprung mass Cg – Roll Center)) / Track

• Geometric Weight Transfer is the source of the Jacking effect.

Jacking Effects:

• Weight Transfer without roll effects.

– Shock movement results from the vertical (up or down) component of the jacking effect.

– This will affect roll angles.

– Will affect mean roll center location

• Because the weight transfer is immediate, tire slip

angles are impacted immediately

– This will affect grip

– This will affect balance

• 1 / Chassis Torsion Rate = 1/ torsion rate front + 1/ torsion rate rear

• Chassis Flex reduces the effective roll resistance

• 1/Total Front Roll Rate = 1/Front combined rate of Springs and ARBs + 1/ Front Chassis Torsion Rate

Some Examples

• Use Jacking to build tire temperatures

• Changing the Jacking effect can change the

balance of a car because of the rate of slip

angle change.

• Use ride height and jacking effect to vary

handling balance in different corners.

• Suspension pickup changes to change RC

height and Jacking effects.

Rollover Moment Arm

Roll Resistance Arm

Jacking Forces

Lateral Acceleration

Tire Reaction Forces

Weight Transfer

Variables for the

Distribution

of

Weight Transfer

(

steady state

)

Roll Centers

– Location plus Vertical and

Horizontal movement

Center of Gravity

-- Location longitudinally

(weight distribution) and vertically

Roll Stiffness

at the wheel -- springs, ARB’s,

chassis trosional rigidity

Longitudinal Weight Transfer

• Anti Dive & Anti Squat = jacking in the

longitudinal axis

• Anti dive substitutes geometric weight

transfer for sprung mass weight transfer. It

does not stop or reduce weight transfer.

• The suspension does not know the

difference between longitudinal resistance

due to braking and due to turning.

Balance made easy;

just

Ride Height - What Me Worry

You bet

• All cornering forces act through the roll

center.

• Springs, anti-roll bars, tire pressures,

and shocks change only the roll

resistance.

• Ride height changes the rollover moment

arm and jacking by changing the roll

center location.

Setup Sheet for

Mitchell Sim.

Mitchell Sim. 2 Ride Height -.25 in.

What is .001 G?

In a 50 mph corner at 1.700 vs. 1.701 G’s

• .02 feet per second

• 1.3 feet every minute

• 52 feet in a 40 minute race

• 3.5 car lengths at the end of the race

What is that worth to you?

What is the cost of imbalance?

The red dot represents 3% unused potential in the right front.

1 0 Gs -1

Deceleration due

to turning in

The car is decelerating at

-.3 Gs from turning resistance alone. Speed Inline Acceleration Brake Pressure Lateral Accel. Steering Mid Ohio

Geometry: no Anti Dive

Instantaneous Axis of Front Suspension

Upper A-arm Plane

Lower A-arm Plane

Chassis Centerline

Cg

Axis's at chassis centerline Of the upper and lower A-arms

Geometry Anti Dive

Instantaneous center front view

Instantaneous center side view

Upper A-arm plane

Lower A-arm plane

Chassis centerline Ground Plane

Front Longitudinal Roll Center

Cg

Front Roll Center

Suspension Geometry in F1

Enough Theory:

Numbers you can use.

• Spring Rates

• ARB Rates

• Chassis Torsion Rate

• Tire Spring Rate

• Motion Ratio = Spring / Wheel movement

• Velocity Ratio = Wheel / Spring movement

Ride Rate / Spring Rate at Tire

• Wheel Rate = (Motion ratio)^2*Spring Rate

• Wheel Rate at the contact patch (WRc) = (Wheel Rate) * (Tire Spring Rate) / (Wheel Rate + Tire Spring Rate)

or 1/WRc = 1/WR + 1/TR

• Ratio 1 = WRc / Corner Sprung Mass

• WRc / Ground Clearance = Constant (close enough to be useful) – This allows you to calculate new ride height for any change of the

WRc.

From page 2 of the Setup Sheet Excel Workbook

Roll Resistance

Those things that resist roll

• Spring Wheel Rates in ft. lbs./degree = (Wheel Rate * ( Sin(1) * Track) / 12)

• Anti Roll Bar Wheel Rates in ft. lbs./degree = Vertical Spring Rate of ARB * ( Sin(1) * Track) / 12

• Roll Rate of Tire at Tire Contact Patch in ft. lbs./degree = Tire Spring Rate * ( Sin(1) * Track) / 12

• Chassis Torsion Rates in ft. lbs./degree (this is calculated in ft. lbs. / degree)

Spring Rate Split = Front Spring Rate / Rear Spring Rate

Roll Stiffness Split = Front Roll Stiffness / (Front Roll Stiffness + Rear Roll Stiffness

% Heave = Front Spring Rate at the Tire / (Front Spring Rate Tire + Rear Spring Rate Tire)

*100

% Corner Rate / Corner Weight = (Spring Rate/ Sprung Corner Weight) * 100

% Corner Roll / Corner Weight = (Roll Rate / Sprung Corner Weight) * 100

Set up Sheet

Roll Stiffness

This sheet is derived from the setup sheet.

Here is an analysis of the set up that is represented by the set up sheet.

Spring Rate Change

Double Spring Rates and

Balance the car by adjusting ARBs

Changing Spring rates without changing Ride Height results in a change of both Spring Rate and Dynamic Ride Height.

Sim. 6 ARB Change

The front ARB is increased to max.

that would still maintain 1.700 G’s

Sim. 7 ARB change

Suspension Friction

&

Torsional Rigidity

2 overlooked and little

understood variables

Suspension Friction

• Suspension friction is the resistance of the

suspension system to any movement. It can

be measured and Friction kills grip.

• Grip is lost because small changes in tire

loading are not absorbed by the suspension

system.

Friction Test the Suspension

• Press the chassis down and release the

pressure.

• Measure the ride height.

• Lift the chassis and let it settle gently.

• Measure the ride height.

• (The difference in the ride height) * 2 *

(spring rate at the wheel) = Force required

to move the chassis.

Excessive Rebound

or Suspension friction • Excessive Rebound does not allow the tire to follow the

ground

– At speed and over short time intervals the chassis is rigid in space preventing the tire from following depressions in the track surface

• The car jacks down over successive bumps over a short time period.

– The frequency of bumps is greater than the chassis frequency of response.

– On successive bumps the force required to displace the suspension increases because of the residual energy retained by the shocks and springs.

– The car skips from top to top.

• The lack of compliance causes the contact patch rubber to loose grip on the surface of the track.

With a under sprung car, adding the rebound feels good because the car gains

support and is more controllable and this improvement is sufficient to mask the loss of grip.

Chassis Stiffness

• Chassis stiffness determines the amount of

roll resistance that can be developed.

• The springs and ARB effectiveness is

reduced by the torsional rate of the chassis.

• A weak chassis requires higher spring and ARB

rates. These rates may be too high to give

Chassis Torsion

Control:

Requires that driver

inputs result in changes in chassis

attitude.

• Steering response

• Stability

• Transition

• Responsiveness

A weak chassis lowers the frequency of the chassis

in roll thus the time/distance it takes for a driver

input to result in a change in attitude increases

Vary directly with

torsional rigidity

FEA model of 94 Citation FF/FC frame

Spring Preload or Droop Limiting

• Any spring preload changes only the amount of

droop before the shock tops out.

• Preload that exceeds the load on the spring to

support the loaded car results in zero droop. At

this point the suspension moves only when the

preload force is exceeded.

• When the shock tops out the dynamic loadings

change:

– Roll resistance from springs and ARB is unchanged, – Roll resistance from tires is unchanged,

– Mean roll center shifts toward inner tire pressure center, – Jacking force decreases and roll center declines.

Spring Pre Load Chart

Thread Pitch = 1 / number of threads per inch Load = ((# of Flats) + ( # of Turns / Flats)) / ( Thread Pitch / Flats per Turn)

Droop Limiting

• Physical roll center is inside tire ground

level

• Additional roll results in decrease in ride

height

• Change in roll resistance – the decrease in

ride height reduces jacking effect

Droop Limited Rear Suspension

Indy Lights at Mid Ohio, Scott Dixon driver

Right Rear Shock topping out

Damper Movement in mm. 0 = full droop

Left Rear Right Front

Left Front

Speed

Bump Rubbers:

use them carefully

• Self dampened springs

• Rising Rate springs

The spring rate is a function of diameter,

length and the material used.

•Larger diameter = higher spring rate

•Longer length = less change in rate with displacement

Disp. Load Rate Load Rate Load Rate .039 2.2 56 10 254 10 254 .079 16.5 363 32 559 20 254 .118 32.12 397 50 457 28 203 .157 58.96 682 63 330 32 102 .197 91.74 833 80 432 38 152 .236 148.5 1442 96 406 42 102 .276 247.5 2515 48 152

Displacement ( ins.), loads (lbs.), and rate (lbs./ins.)

Dynamics Ohlins Penske

Bump Rubbers and Packer

Fix first problems first

Straight line stability

Braking

Corner Entry

Mid Corner

Corner Exit

Be certain you identify where the problems start.

Be sure to analyze the entire corner instead of concentrating on the problem area.

Tuning at track

Ground Clearance: Initial setting of the ride height.

Spring rates: Road springs, ARB’s, Bump Rubbers,Tires pressures Suspension travel: How much bump and droop – preload

Ride height: Adjusting Center of Gravity, Roll Centers, and Jacking Effects Tire Presentation to the ground – contact patch

Camber, caster, KPI, Roll Toe, Tire Pressure Aero Loads and Balance – Flat bottom ground effects

Rake and ride height

Weight Distribution and Moment of Inertia in Yaw

Algorithm for chassis adjustments

• Identify the problem to be solved.

• Identify the handling features not to change.

• Identify the attitude change that will solve

the handling problem.

• List the changes that will lead to the attitude

change.

• Evaluate the proposed changes.

– Will it fix the problem.

Chassis Changes

• Most solutions will require changing two or

more variables.

• Make sure that when you make a change

that you identify all the variables you have

changed.

– Spring changes require ride height changes.

– Wing changes require ride height changes.

– ARB changes may require spring changes.

Real World Examples 1

• Corner exit over steer

– Is it throttle induced?

• Change balance of rear ARB and rear springs • Rear ride height

– Is it steering induced?

• More roll resistance front • Run Sheet information:

– Entry is good, mid corner is alright, but I can’t apply power

without the rear stepping out. The tire temps show a slight push - avg. front temps 15 degrees higher than rear.

• What to do?

– Entry alright, mid corner same, but as I exit the corner the rear steps out. Temps show a slight under steer.

Real World Examples 2

• High Speed over steer / low speed under steer

– Insufficient roll control: stiffer springs and/or ARB’s – Goal is to get the car to under steer every where then

fix that problem.

– Adjust roll center through ride height changes.

• Run Sheet information:

– Car is not too good. I have a hard time getting the car to turn in to the slow corners and get down to the apex. The fast corners the rear wants to come out about mid corner of later. Tire temps show push and are not

particularly high.

Elkhart / Gingerman Springs Example 3

• Elkhart Carousel

Track induced Over Steer

•Gingerman sweepers

Throttle induced Over Steer

Over-steer in mid corner power on at both tracks.

Increase spring rate & Lower Rear Ride Height

Under-Steer

:

a second look Re think

• Under-steer because the front tires are under

utilized.

– Stiffer front roll resistance

• Under-steer because the front tires are over

stressed.

– Less front roll resistance or more rear roll

resistance

• Driver induced under-steer.

– Does the driver lack confidence in the setup?

– Can the driver change technique?

Driver induced Under Steer

Difference in minimum speed

Higher lateral G loading late in the corner

Problem:

Carrying too much speed into the corner.

Not getting enough rotation or yaw in to the car prior to apex. Too much of the cornering effort is done near the corner exit

Aerodynamic Devices - basics

Ground effects –

• All cars are ground effects cars. The larger the plan area of the car the greater the down-force possible.

• Center of Pressure varies with chassis rake (pitch)

• Down-force varies with ride height.

Wings –

• Front wings and end plates

• The drag from the front wings is offset by the reduction in the drag associated with the rest of the car. Front wings frequently stall at angles of 6 degrees.

• Rear Wings and end plates

• The air flow to the rear wing is seldom horizontal but is down swept from

passing over the rest of the car. Thus the optimum attack angle might be nose high. Rear wing drag increases with down-force.

• Measuring wing angles

• Include the Gurney/wicker in the wing angle. Down force will be close when the angles are equal with and without Gurney’s.

Front Wings

Rear Wing

Gurney Flap Slider Dual Element

Dual Element Upper

Single Element Lower

Flat bottom with diffusers and tunnels

Adjust Ride Height with air density

• Standard Atmosphere -

29.95 Hg and 15 C (68 F)

• Barometric Pressure –

lower pressure is lower air density

• Temperature Adjustment –

Higher Temp less down force

• Humidity Adjustment –

Higher humidity lowers air density

Real World Example 4

• Push Low to Medium Speed Turns.

– Imbalance in high speed and low speed

handling.

– Goal: better low speed balance without

upsetting the high speed balance

• Solution:

– More rear wing and higher rear ride height.

– The improved corner exit speed offsets the loss

in top speed.

Fundamentals of Shock Absorbers

Various types of shocks

•Double or Twin Tube

•Gas Filled with internal and external Gas Chambers

Types of adjusters

•Needle valves adjusters •Spring preload adjusters •Blow Off adjusters

Canister pressure

•Why canister pressure

Piston Style

•Linear or Digressive

•Flat or Dished Face

•Cupped Face

•Bleed Holes &/or Bleed Shims

Adjustment Ranges

•Low Speed

•Mid range

•High Speed

Piston Style

1. Linear 2. High-flow linear 3. Digressive / linear 4. Digressive / digressive 5. Velocity-dependent (VDP) 6. Digressive blow-off

• Bleed holes &/or bleed shims

Adjustment Ranges

• Low-speed – piston or needle bleeds

• Mid-range • High-speed

Damper Fundamentals (2)

1 2 3 4 5 6 BLEED EFFECT BLEED EFFECTS

Rebound Canister in compression or bump

Compression or Bump

Ohlins T44

Rebound

Shock Histogram

Most damper motion is at velocities below 1 in/sec.

Force vs. Velocity

Compression stroke starts

Compression reaches max. velocity This is the midpoint in the stroke Compression ends and rebound stroke starts

Crank is at top

Gap shows gas pressure effect

Rebound reaches max. Gap shows the hysteresis

Average Force vs. Velocity

These curves are the average of the curves in the previous slide

These curve shows the same shock but at a different crank rotational velocity

1 in/sec. Max velocity

Force vs. Displacement

Dyno crank position bottom of stroke Crank is at max velocity compression stroke

Dyno is at top of stroke Max velocity Rebound

Note the sloop and sharp brake on curve

Stroke at 5 in/sec.

Gas Pressure NOT Zeroed

Front & Rear Shocks

Front Shock @ 5 in/sec

Front Shock @ 1 in/sec.

Rear Shock @ 5 in/sec.

Critical Damping

• That amount of damping which results in the

quickest stabilization at new position.

• That amount of damping that will maximize

GRIP

• That amount of damping that stops the chassis

over shooting.

Rebound Kills Grip

• Insufficient Rebound damping allows the

chassis to over shoot as the spring extend.

– This results in a loss of grip as the wheel

follows the chassis upward.

• Excessive rebound retards the downward

movement of the wheel.

– This results in a loss of grip as the wheel

follows the chassis and not the road surface.