race seminar

7/31/2019 Race Seminar

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Race Car Engineering

2004


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Good Handling is

Grip= tires operating at maximumadhesion to the track surface.

Balance=both ends of the car areoperating harmoniously, the car instillsconfidence and is fun to drive.

Control = the car responds quickly andpredictably to driver inputs, you can makethe car do what you want it to do.


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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

Grip enhancers and killers


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Balance

Weight transfer

Relative Front and Rear Slip Angles

Car rotation

Consistency in fast and slow corners

Transitions


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Control

Steering response

Stability

Transition

Responsiveness

Progressiveness Driver comfort and confidence


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Axiom 1

If you want to corner at 2 Gs you have to

support the car for 2 Gs forces.

Regardless of the individual setups, two

similar cars cornering at the same speed

will have to deal with the same forces.


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Outline

Notes on chassis alignment & Record keeping

Grip = Tires: Slip angle and Grip

Balance = Suspension Geometry Static Analysis

= Suspension Dynamics &Weight Transfer

Control = Chassis tuningwithout shocks

= Chassis tuningbump rubbers and

droop limiting= Shocks

Data Loggers = What have I done?


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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


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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.


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Most drivers can not tell the difference between animprovement in control and an improvement in grip

A car is supported during cornering through the

combination of Springs, ARBS, Shocks, andDynamic Suspension Geometry.

The line a car takes through a corner is moredependent on the car setup than the drivers

technique.

Consistently fast cars are easy to drive.

More Facts


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Good Setups are the product of hardwork 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 helpyou correct the car when it is not fast.


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94 FC Citation


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Chassis Setupsrequire

Accuracy:2001 SCCA Runoffs percentage that 10th qualifierwas 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 cumbersomeyou will not maintain the accuracy through out an event. The system must be

portable.


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You should do your work with a degree

of accuracy that this race was decided.


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Equipment You Make

Ride Height Gauge

Bump Steer Gauge

Alignment Flags

Toe Bars and trammel bars

Trammel Pins

Shock Struts


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Bump Steer

GaugePlate 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.


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Ride Height Gauge

TrammelPin

2 Useful Tools


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Procedures - Sequence

Set ride height

Zero toe settings

Adjust camber

Adjust caster

Zero toe settings and take new readings

Repeat the process until correct

Adjustments are inter related


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Use to set Camber, Toe, Ride Height

Flag Alignment System

1.5 Square Tubing

Plate

Measure the gap

20 in.


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Alignment Notes

Do setups without driver but with

representative fuel load.

Check the setup before and after running thecar.

Have an alignment process for home and a

checking procedure for the track.


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Setup Work

SheetThis is an example of a work

sheet for recording the settings as

you progress through thealignment process


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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 incase a suspension arm needs to be replaced


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Suspension

Build Sheet

The idea is to keep good

and accurate records of

the setup


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Chassis Data

Sheet

This Sheet contains information to

help make quick and accurate

adjustments.


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Corner Weight and Ride HeightOnce 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 thechassis

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


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Corner Weight Discrepancy


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Record Keeping


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The Set Up Sheet should contain all

the necessary information to reproducethe exact settings.

Additionally, the set up sheet cancontain any additional information togive a better understanding of the

particular setup.

Set Up Sheet

Page 1


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The Run Sheet is the record

of all the on-track activity.

Additionally it may show thestarting set up as a referenceto help decide what changesare appropriate.

When the session is over,the Run Sheet gives acomplete record, showingthe beginning, allintermediate steps, and theending setup.

The Run Sheet is the recordof the performance for anygiven setup.

Run Sheet


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This is an example of therun sheet

This sheet shows where thesetup was at the beginning of

lap 80.

It shows the lap times foreach outing, the amount offuel, the drivers commentsfor that outing, and the setup

changes that were in effectfor that outing.

Run Sheet


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This is the formal and necessary

review of the time on the track.

Combined with the chassis set downsheet, this sheet is guide to the futurechanges in the set up.

This is the most neglectedaspect of record keeping.The driver always has morepressing things to attendto such as girls and glory.This sheet when properlyexecuted is the best key toa better setup.

Driver Debrief Sheet


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An alternative form of the driver Debrief Sheet

Using a map to make notes on is easier andsometimes more helpful. It is also easier to

leave out important details. Make a check listto be sure that all details of the debrief arecovered

Debrief Map


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G


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Gearing: How to select gears

1. Determine the lowest speed at which you can apply fullpower. This speed should correspond to maximum torquein 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 dropbetween successive gears is constant or declines slightlyas speed increases.

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


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Gear Ratios

This Sheet presents both

graphic and analytical toolsfor analysis ratio selections.

The right hand (shaded)portion of the charts showscritical speeds and the RPM

for that speed in each gear.

The graph is a way ofviewing the RPM drop foreach gear change.

The top chart has the ratios

from the Setup Sheet.

The lower chart is used as awork sheet to try alternativeratios.


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Ti Di t ti Sli A l


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Tire DistortionSlip Angle

H d i d l GRIP?


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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

rubber to conform to the track surface


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Avon TiresFront Tires Rear Tires

150 kg = 331 lbs

250 kg = 551 lbs

350 kg = 772 lbs


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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 theoutside tires.

Less weight transfer will result in greater totalcornering force.


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Things to Increase Grip:

Press the tire into the track surface

harder.

Increase the time the tire has to conformto the track surface.

Increase adhesion between the tire and

the track surface

Sli k Z f Ti T


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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 lateralforce 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.


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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

*When driving a car around a corner*


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Contact Patch DistortionTire Foot Print


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Steering: no slip angle

Balanced or neutral corneringSlip angles are equal

Steering is Full Ackerman Geometry

InstantaneousCenter of Rotation


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Cornering: 5 deg. Slip angle

Outside tires have equalSlip angles. Thus neutral orbalanced handling

Corner radius is constant ( 20.7 ft.)


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Cornering: 8 deg. Slip angle

The steering angle of the frontwheels is nearly constant for all theslip angle conditions (decreasingless than a degree).


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Cornering: combined illustrations

This is the path of theinstantaneous center

of rotation given aconstant radius andvarying slip angle forthe outside tires.

This illustrates a balancedcornering condition.

0 degrees

5 degrees

8 degrees


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Under Steer vs. Over Steer


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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 steeringlock with speed.


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Notice the tire distortion. The

front tires are turned to balancethe front and rear slip angles andadjust the corner radius. The caris tracking around the corner.

Slip Angle


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There is no cornering force

without

and

preload

the

Friction Circle 2.5Acceleration


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Friction Circle

Ft max = maximum G of about

1.25 acceleration and 1.25cornering.

-2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0

Lateral Gs Left Turn

2.0

1.5

1.0

0.5

-0.5

-1.0

-1.5

-2.0

-2.5

Lateral Gs 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


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Friction Circle and theCombined G Graph

Speed

Combined Gs

Mid Ohio

Note: Slower and earlier entry to the corner

along with the higher minimum and higherexit speed.

Better utilization of the

carspotential

F i ti Ci l d bi d G


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Friction Circle and combined Gs

Speed

Combined Gs

Throttle

Note: the early setup and power application

Laguna Secca.


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Tire management and understanding


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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.

How to read car balance before you hurt the tires


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Temperature across the tire. Temperatures frontto rear. Tire pressure rise is more accurateindication of car balance.

How to maximize tire life

Determine the balance of a car before the tiresare damaged. Rotate tires after a predeterminednumber of laps. Dismount and reverse on therim.

Recommended number of wheels - 14 - toreduce tire costs

How to read car balance before you hurt the tires


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Getting the tire pressure correct is vital to goodperformance 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 tirepressure adjustments to adjust new sets.

Tire pyrometer use

Where to stick the needle. Consistency is vital.Measure quickly after a run.

Tire pressure management


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Tire Pressure Compensation


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Tire Record

If you have a tire

man, make him work.


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Steering

Geometry:

Balance &

Control


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S i A i


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Steering Axis

King Pin Inclination

King Pin Axis

Camber Angle

Front View

St i A i


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Steering Axis

Caster

Front

Caster Trail

Steering Axis

Side View

Steering Axis


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Steering Axis

Scrub Radius

KP Axis at groundSteering TrailSteering offset

Pressure Center Front

Bottom View

Steering Axis


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Steering Axis

Front

Three Dimensions

Steering Axis: So What ?


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Steering Axis: So What ?

Caster causes the front wheels to lean in the

direction of the turn.


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Caster and Steering Axis

Tire Contact Point

Steering Axis

P t


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Plane of

Steering Axis

Pure caster causes

the tire to lean in

the direction

of the turn.

King Pin Inclination (KPI)


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King Pin Inclination (KPI)

Steering Axis

Ground

Plane of Rotation

KPI Pure, no


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KPI Pure, noCaster

Steering Axis

Spindle

Steering Plane

Ground


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KPI + Caster


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Scrub radius causes longitudinal

forces at the contact patch togenerate torque about the steering

axis.Caster combined with trail causes

steer dive when the wheels are

steered from center.


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Steering Axis 2Steering Axis may be offset rearward from the wheelcenter to reduce Caster Trail and thus reduce the steeringeffort.

Steering Axis Offset

Caster Trail = 0

Lola T97 Indy LightsExample


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Straight Ahead

Suspension as in turn 1 MO 2.5 Gs lateral acceleration


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Steering is straight

Roll angle

Suspension displacement istaken from the damperdisplacement data.

.227 deg

Roll Center is 1.366 Right and -.941 below ground

Steering geometry makes a difference


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Roll was .227Now .417 withsteering input

Roll Center was 1.366 to the rightNow it is 3.594 left

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

F ll A k S i G


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Full AckermanSteering Geometry

All wheels steer about a common point

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

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

20 deg. 25.7 deg.

Example: corner push with


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a p e: co e pus w t

exit snap over steer

Driver says entry all right, mid corner mild understeer, but corner exit the rear steps out.

Tire temperatures are normal or front tires are

cooler than the rear. Tire pressure rise for fronttires is same or less than the rear.

Problem is that the car is under steering. But atthe exit, as the steering wheel is straightened, the

grip on the outside front tire increases causing thefront to turn more in the direction that the frontwheels are headed. Result the rear steps out.


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More about Camber


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More about Camber Camber causes an uneven distribution

of pressure on the contact patch.

The inner edge of the tire is compressedmore than the outer edge.

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

The uneven pressure results in alateral force, Thrust, in the directionof the camber.

The thrust preloads the slip anglecausing lateral stability.

Camber increases grip by increasingthe load on the inner edge of the tire.

Camber Shifts the friction Circle rightthus increasing lateral grip.

Thrust

More about Toe


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More about Toe Toe preloads the Slip Angle.

Slip angle creates lateral gripand lateral thrust.

Slip angle increases lateralstability.

Front toe out counteracts frontcamber thrust.

Rear toe out can help cornertransitions.

On a driven wheel toe increases

rolling resistance. On a drive wheel toe has little

effect.

Front

Toe in

Toe out


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Ch i


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Chassis

Balance

Chassis

Dynamics

Chassis Dynamic Movements:


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6 Degrees of Freedom

Movement Along the three axis'sLongitudinal axis Acceleration & DecelerationLateral axis Lateral Acceleration or TurningVertical axis Change in ride height

Rotation about the three axisRoll about the longitudinal axisPitch about the lateral axis

Yaw about the vertical axis

A vehicle suspension system controls the movementsof the vehicle in all three axiss, restraining the six

degrees of freedom.




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Controlling Chassis Dynamic Movement


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g yis the key to a

Balanced Setup.

Controlling weight transfer, Controlling slip angle development.

Suspension Geometry, Springing and Dampingare the main mechanisms to achieve balance.

This is done by:

Suspension Kinematics 1


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Instantaneous Center

The instantaneous point about which an individualwheel rotates in bump (vertically).

Roll Center

The roll center is the intersection of the two linesformed between the tire contact patch and theirrespective instantaneous centers.

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

Mean Roll Center Height

The point about which the body rolls.

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


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Theroll centeris 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.



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Suspension Dynamics


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Suspension Dynamics

Pull the handle slowly and the glass will move across the table.

Pull the glass faster and the glass will fall over.

Pull the handle fast enough and the glass stays put.

Suspension Dynamics


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Suspension Dynamics

Stationary

Pull

Un-sprung Mass Weight Transfer

CG

Lateral Acceleration acts through the center of gravity ( )

2 Wheels


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Pull

CG

Lateral Acceleration

Reactive Force / Grip

Stationary

Weight Transfer

Weight Transfer

Sprung Mass


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Pull

Lateral Force

Sprung Mass weight transfer


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with Springs

R/C

Pull

Lateral Force

Traction Force acts through the R/C

Un-sprung Mass

Weight Transfer

Sprung Mass Weight Transfer

Geometric Weight Transfer

J ki F


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Jacking Force

R/C

Geometric Weight Transfer

J ki F


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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 MassLateral Force

Lateral Weight Transfer


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Un-sprung Weight Transfer = (un-sprung mass * Lateral

Acceleration * non-suspended mass Cg height ) / Track

Geometric Weight Transfer = ( Sprung mass * LateralAcceleration * Roll Center Height) / Track

Sprung Mass Weight Transfer = (Sprung mass * (Sprung

mass CgRoll Center)) / Track

Geometric Weight Transfer is the source of the Jacking

effect.

There are three components of lateral weight transfer

Jacking Effects:


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g

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 slipangles 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


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Some Examples

Use Jacking to build tire temperatures

Changing the Jacking effect can change the

balance of a car because of the rate of slipangle change.

Use ride height and jacking effect to varyhandling balance in different corners.

Suspension pickup changes to change RCheight and Jacking effects.

Kinematics Illustrated


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Rollover Moment Arm

Roll Resistance ArmJacking Forces


Tire Reaction Forces

Weight Transfer


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Weight Transfer



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Longitudinal Weight Transfer

Anti Dive & Anti Squat = jacking in thelongitudinal axis

Anti dive substitutes geometric weighttransfer for sprung mass weight transfer. Itdoes not stop or reduce weight transfer.

The suspension does not know the

difference between longitudinal resistancedue to braking and due to turning.


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Ride Height - What Me Worry


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Ride Height What Me Worry

You bet

All cornering forces act through the rollcenter.

Springs, anti-roll bars, tire pressures,and shocks change only the rollresistance.

Ride height changes the rollover moment

arm and jacking by changing the rollcenter location.

Setup Sheet for


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Mitchell Sim.

Mitchell Simulation


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Mitchell Sim. 2 Ride Height -.25 in.


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The original was 1.700 Gs lateral


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What is the cost of imbalance?


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

That is .14 ft./sec., 8.4 ft./min., or 336 feet at the end of a 40 min. race.

Summary of Sim. # 1 to 4


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Deceleration due Speed


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1

0 Gs

-1

to turning in

The car is decelerating at-.3 Gs from turning resistance

alone.

Inline Acceleration

Brake Pressure

Lateral Accel.

Steering

Mid Ohio

G t A ti Di


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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


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Suspension Geometry in F1N t th j ki ff t th f t i


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Note the jacking effect on the front suspension


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Enough Theory:


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g y

Numbers you can use.

Spring Rates

ARB Rates

Chassis Torsion Rate Tire Spring Rate

Motion Ratio = Spring / Wheel movement

Velocity Ratio = Wheel / Spring movementAllow us to derive the following:

Ride Rate / Spring Rate at Tire


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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 ResistanceThose things that resist roll


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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)

Total Resistance at one end is the sum of 7 spring rates.

Magic Ratios


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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

g

Set up Sheet

Roll Stiffness


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Roll Stiffness

This sheet is derived from thesetup sheet.

Here is an analysis of the set upthat is represented by the set up

sheet.

Spring Rate Change


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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.


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Summary of Sim # 1 to 5


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Summary of Sim. # 1 to 5

Sim. 6 ARB Change


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The front ARB is increased to max.

that would still maintain 1.700 Gs

Sim. 7 ARB change


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Rear ARB is removed and the car is balanced by adjusting the front ARB.

Summary of Sim. changes


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Set Up Sheet Page 3


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S i F i ti


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Suspension Friction

&Torsional Rigidity

2 overlooked and little

understood variables

Suspension Friction


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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


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Friction Test the Suspension

Press the chassis down and release thepressure.

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 requiredto move the chassis.

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


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ground

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

The car jacks down over successive bumps over a shorttime period.

The frequency of bumps is greater than the chassis frequency of

response. On successive bumps the force required to displace the suspensionincreases because of the residual energy retained by the shocks andsprings.

The car skips from top to top.

The lack of compliance causes the contact patch rubber toloose 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


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Chassis Stiffness

Chassis stiffness determines the amount of

roll resistance that can be developed.

The springs and ARB effectiveness isreduced by the torsional rate of the chassis.

A weak chassis requires higher spring and ARB

rates. These rates may be too high to give

acceptable ride and grip levels.

Chassis Torsion


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For a chassis of 1500 ft.-lbs./deg. the roll rates are Front 454 and Rear 315 ft.-lbs./deg.

Control:Requires that driveri t lt i h i h i


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inputs result in changes in chassis

attitude. Steering response

Stability

Transition

Responsiveness

A weak chassis lowers the frequency of the chassisin 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


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94 FF

94 Citation at Mid Ohio


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94 Citation at Mid Ohio


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Spring Preload or Droop Limiting

Any spring preload changes only the amount of


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Any spring preload changes only the amount ofdroop before the shock tops out.

Preload that exceeds the load on the spring tosupport the loaded car results in zero droop. Atthis point the suspension moves only when thepreload force is exceeded.

When the shock tops out the dynamic loadingschange:

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 inchLoad = ((# of Flats) + ( # of Turns / Flats)) /( Thread Pitch / Flats per Turn)


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Droop Limiting


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Physical roll center is inside tire groundlevel

Additional roll results in decrease in ride

height Change in roll resistancethe decrease in

ride height reduces jacking effect

Change in weight transfer or wedging

Droop Limited Rear SuspensionIndy Lights at Mid Ohio, Scott Dixon driver


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Right Rear Shock topping out

Damper Movement in mm. 0 = full droop

Left Rear

Right Front

Left Front

Speed

Notice Change in Ride Height with Speed

Bump Rubbers: use them carefully


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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

displacementBy shaping the race can be altered

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

Dynamics Ohlins Penske


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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

Bump Rubbers

Bump Rubbers and Packer


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Packer in 1/8th in.


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Fix first problems first


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Fix first problems first

Straight line stability

Braking

Corner Entry

Mid Corner

Corner ExitBe certain you identify where the problems start.

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

Tuning at trackGround Clearance: Initial setting of the ride height.


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g g

Spring rates: Road springs, ARBs, 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 patchCamber, caster, KPI, Roll Toe, Tire Pressure

Aero Loads and Balance Flat bottom ground effectsRake and ride height

Weight Distribution and Moment of Inertia in YawFuel load, ballast position, driver seating position

Algorithm for chassis adjustments

Identify the problem to be solved.


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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 attitudechange.

Evaluate the proposed changes.

Will it fix the problem.What are the adverse effects from the change.

Chassis Changes


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g

Most solutions will require changing two ormore variables.

Make sure that when you make a change

that you identify all the variables you havechanged.

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


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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 cant apply powerwithout 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. What to do?

Real World Examples 2 High Speed over steer / low speed under steer


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Insufficient roll control: stiffer springs and/or ARBs

Goal is to get the car to under steer every where thenfix 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.

What to do?

Elkhart / Gingerman Springs Example 3

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


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Elkhart CarouselTrack induced Over Steer

Gingerman sweepersThrottle induced Over Steer

Increase spring rate & Lower Rear Ride Height

Lower Spring rate & Raise Rear Ride Height

Under-Steer: a second look Re think

Under-steer because the front tires are under


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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


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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

Wings


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Aerodynamic Devices - basicsGround effects All cars are ground effects cars. The larger the plan area of the car the greater


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

Center of Pressurevaries 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 associatedwith 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 frompassing over the rest of the car. Thus the optimum attack angle might be nosehigh. Rear wing drag increases with down-force.

Measuring wing angles Include the Gurney/wicker in the wing angle. Down force will be close when theangles are equal with and without Gurneys.

Front Wings

Rear WingWings:


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Front Wings

GurneyFlap

Slider

Dual Element

Dual Element Upper

Single Element Lower

Mitchell Sim.: 100 lbs Down Force


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Flat bottom ground effects, winged formula car


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Flat bottom with diffusers and tunnels

Ground Effects


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Adjust Ride Height with air density


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Standard Atmosphere -29.95 Hg and 15 C (68 F)

Barometric Pressurelower pressure is lower airdensity

Temperature AdjustmentHigher Temp lessdown force

Humidity AdjustmentHigher humidity lowersair density

Ride height / air density ratio is constant

Aero Adjustment of Ride Height


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Real World Example 4


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Push Low to Medium Speed Turns.

Imbalance in high speed and low speedhandling.

Goal: better low speed balance withoutupsetting the high speed balance

Solution:

More rear wing and higher rear ride height.

The improved corner exit speed offsets the lossin top speed.


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Fundamentals of Shock Absorbers


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Various types of shocksDouble or Twin TubeGas Filled with internal and external Gas Chambers

Types of adjustersNeedle valves adjustersSpring preload adjustersBlow Off adjusters

Canister pressureWhy canister pressureLow speed bump adjuster

Piston StyleLinear or Digressive


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Linear or Digressive

Flat or Dished FaceCupped FaceBleed Holes &/or Bleed Shims

Adjustment RangesLow SpeedMid rangeHigh Speed

Piston Style

Damper Fundamentals (2)

1


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y

1. Linear 2. High-flow linear3. Digressive / linear4. Digressive / digressive5. Velocity-dependent (VDP)

6. Digressive blow-off Bleed holes &/or bleed shims

Adjustment Ranges Low-speed piston or needle bleeds

Mid-range High-speed

2

3

4

5

6

BLEEDEFFECT

BLEEDEFFECTS

Rebound Canister in compression or bump


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Penske 8760

Compression or Bump Rebound


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Ohlins T44

Shock Movement


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Shock Velocity


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Shock Histogram


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

This is the most critical range to develop grip and handling

Compression ends and rebound stroke starts

Crank is at top


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Force vs. Velocity

Compression stroke starts

Compression reaches max. velocity

This is the midpoint in the stroke

Gap shows gas pressure effect

Rebound reaches max.

Gap shows the hysteresis

Average Force vs. Velocity


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g y

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

5 in/sec. Max velocity


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Force vs. Displacement

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

Dyno is at top of strokeMax velocity Rebound

Note the sloop and sharp brake on curve

Stroke at 5 in/sec.

Stroke at 1 in/sec.


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Gas Pressure NOT Zeroed

The offset shows the nose pressure or gas pressure that the shock exerts on the dyno load cell..


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Front & Rear Shocks

Front Shock @ 5 in/sec

Front Shock @ 1 in/sec.

Rear Shock @ 5 in/sec.

Rear Shock @ 1 in/sec.


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Critical Damping


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That amount of damping which results in thequickest 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


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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 downwardmovement of the wheel.

This results in a loss of grip as the wheel

follows the chassis and not the road surface.

More rebound does not make the tire stick to the ground

Shock Tuning 1


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High speed canister bump -- is there enough support or too harsh overbumps

Low speed Canister Bumptoo stiff or too soft , too harsh or not enough

support

Reboundalways try to use the least amount of rebound possible.

More rebound than optimum reduces grip.

Low Speed Bump (bleed)optimizes grip. With too much bleed the car

does not respond and feels unsupported. Too little bleed reduces grip

and causes the tire alternate between grip and slip.

Adjust Low Speed Bump and Rebound together, both stiffer or softer, to

optimize damping for track conditions.

AdjustmentMore Compression More Rebound

More Canister Larger Bleed

Shock Tuning 2


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More Compression More ReboundPressure Area

Location High-speed Low-speed High-speed Low-speed

Front

More front un-

sprung mass

control, possible

excess

suspension loads

over bumps orcurbs, possible

loss of grip over

bum s

Less front chassis

drop, less trailing-

throttle oversteer,

possible loss ofgrip

Better front un-

sprung mass

control, possible

loss of front gripover bumps

Less front chassis

rise, less power-

on understeer,

possible loss ofgrip

More front height

control, possibly

less front grip

Shallower nose

angle, more front

grip, possible loss

of low-speed frontchassis control

Rear

More rear un-

sprung mass

control, possible

excesssuspension loads

over bumps or

curbs, possible

loss of grip over

bum s

Less rear chassis

drop, less power-on understeer,

possible loss of

grip

Better rear un-

sprung masscontrol, possible

loss of rear grip

over bumps

Less rear chassis

rise, less trailing-throttle oversteer,

possible loss of

grip

More rear heightcontrol, possibly

less rear grip

Shallower nose

angle, more reargrip, possible loss

of low-speed rear

chassis control

Data Loggers What data loggers wont do:

Data loggers wont tell you whats wrong,

Data loggers wont tell you what to do


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Data loggers won t tell you what to do.

What will a data logger tell you: Data logging tells you what the sensors read at various points around the

track and in a fixed time frame.

You must interpret the data.

The data loggers record the resultof the interaction of thedriver, the car and the track.

The data logger takes a snap shot of all the sensors at a

point in time, often recording the readings sequentially.

The driver and the data logger are seldom in sync witheach other. The driver operates in anticipation of what he

expects the car to do and adjusts according to his senses.

Data Logging 2 Car Performance Channels

Time recording hertz

Speed - wheel speed sensor Track Map


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Speed wheel speed sensor

Accelerometerlateral and longitudinal

Driver Performance Channels Steering wheel movement

Throttle position

Brake Pressure

Other Data Channels Damper Pots

Strain gauges

Ride height sensors Gyro

Vertical accelerometer

Track Map

Fundamental Analysis

Advanced Analysis

Math Channels

Math Channels

Wh l M D i * M i R i


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Wheel Movement = Damper motion * Motion Ratio

Chassis Roll = (L Wheel mvt.R Wheel mvt.)/ Track

Chassis Pitch = (LF Wheel mvt + RF Wheel mvt) / 2

( LR Wheel mvt + RR Wheel mvt) / 2

Speed Steer = Steering Angle * MPH * (MPH)^.5 Corner Radius = (1.467 * MPH)^2 / (32.167 * Lateral Gs)

Combined Gs = ((Lateral Gs)^2 +

(Longitudinal Gs)^2)^.5

Gear = MPH / (RPM / 1000)


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