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  1. #1
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    Default Car setup - cause and effect

    Great thread nicked from SJC, interesting read


    Carroll Smith's Cause and Effect Guide

    RIDE AND ROLL RESISTANCE-SPRING

    Too much spring: overall
    Harsh and choppy ride
    Much unprovoked sliding
    Car will not put power down on corner exit - excessive wheel-spin

    Relatively too much spring: front
    Understeer - although the car may initially point in well
    Front breaks loose over bumps in corners
    Front tyres lock while braking over bumps

    Relatively too much spring: rear
    Oversteer immediately on application of power
    Excessive wheel-spin

    Too little spring: overall
    Car contacts the track a lot
    Floating ride with excess vertical chassis movement, pitch and roll
    Sloppy and inconsistent response
    Car slow to take a set ? may take more than one

    Relatively too little spring: rear
    Excessive squat on acceleration accompanied by excessive rear negative camber, leading to oversteer and poor power down characteristics
    Tendency to fall over on outside rear tyre and "flop" into oversteer and wheel-spin

    ANTI-ROLL BARS

    Too much anti-roll bar: overall
    Car will be very sudden in response and will have little feel
    Car will tend to slide or skate rather than taking a set - especially in slow and medium speed corners
    Car may dart over one wheel or diagonal bumps

    Relatively too much anti-roll bar: front
    Corner entry understeer which usually becomes progressively worse as the driver tries to tighten the corner radius.

    Relatively too much anti-roll bar: rear
    If the imbalance is extreme can cause corner entry oversteer
    Corner exit oversteer. Car won't put down power but goes directly to oversteer due to inside wheel-spin
    Excessive sliding on corner exit
    Car has a violent reaction to major bumps and may be upset by "FIA" kerbs

    Too little anti-roll bar: overall
    Car is lazy in response, generally sloppy
    Car is reluctant to change direction in chicane and esses

    Relatively too little anti-roll bar: front
    Car "falls over" onto outside tyre on corner entry and then washes out into understeer
    Car is lazy in direction changes

    Relatively too little anti-roll: rear
    My own opinion is that on most road courses a rear anti-roll bar is a bad thing. Anti-roll bars transfer lateral load from the unladen tyre to the laden tyre - exactly what we don't want at the rear. I would much rather use enough spring to support the rear of the car. The exception comes when there are "washboard ripples" at corner exits, as on street circuits and poorly paved road circuits.

    SHOCK ABSORBER FORCES

    Too much shock: overall
    A very sudden car with harsh ride qualities, much sliding and wheel patter
    Car will not absorb road surface irregularities but crashes over them

    Too much rebound force
    Wheels do not return quickly to road surface after displacement. Inside wheel in a corner may be pulled off the road by the damper while still loaded
    Car may "jack down" over bumps or in long corners causing a loss of tyre compliance. Car does not power down well at exit of corners when road surface is not extremely smooth

    Too much bump force: general
    Harsh reaction to road surface irregularities.
    Car slides rather than sticking
    Car doesn't put power down well - driving wheels hop.

    Too much low piston speed bump force
    Car's reaction to steering input too sudden
    Car's reaction to lateral and longitudinal load transfer too harsh

    Too much high piston speed bump force
    Car's reaction to minor road surface irregularities too harsh - tyres hop over "chatter bumps" and ripples in braking areas and corner exits.

    Too little shock: overall
    Car floats a lot (the Cadillac ride syndrome) and oscillates after bumps
    Car dives and squats a lot
    Car rolls quickly in response to lateral acceleration and may tend to "fall over" onto the outside front tyre during corner entry and outside rear tyre on corner exit.
    Car is generally sloppy and unresponsive

    Too little rebound force: overall
    Car floats - oscillates after bumps (the Cadillac ride syndrome)

    Too little bump force: overall
    Initial turn in reaction soft and sloppy
    Excessive and quick roll, dive and squat

    Too little low piston speed bump force
    Car is generally imprecise and sloppy in response to lateral (and, to a lesser extent longitudinal) accelerations and to driver steering inputs

    Too little high piston speed bump force
    Suspension may bottom over the largest bumps on the track resulting in momentary loss of tyre contact and excessive instantaneous loads on suspension and chassis

    Dead shock on one corner
    A dead shock is surprisingly difficult for a driver to identify and/or isolate
    - At the rear, the car will "fall over" onto the outside tyre and oversteer in one direction only
    - At the front, the car will "fall over" onto the outside tyre on corner entry and then understeer.

    WHEEL ALIGNMENT

    Front toe-in: too much
    Car darts over bumps, under heavy braking and during corner entry - is generally unstable
    Car won't point into corners, or if extreme. May point in very quickly and then dart and wash out

    Front toe-out: too much
    Car wanders under heavy braking and may be somewhat unstable in a straight line, especially in response to single wheel or diagonal bumps and/or wind gusts
    Car may point into corners and then refuse to take a set
    If extreme will cause understeer tyre drag in long corners

    Rear toe-in: too little
    Power on oversteer during corner exit

    Rear toe-in: too much
    Rear feels light and unstable during corner entry. Car slides through corners rather than rolling freely

    Rear toe-out: any
    Power oversteer during corner exit and (maybe) in a straight line
    Straight line instability

    Front wheel caster or trail: too little
    Car too sensitive (twitchy?)
    Too little steering feel and feedback

    Front wheel caster or trail: too much
    Excessive physical steering effort accompanied by too much self return action and transmittal of road shocks to the drivers hands
    General lack of sensitivity to steering input due to excessive force required

    Front wheel caster or trail: uneven
    Steering effort is harder in one direction than in the other
    Car will "pull" towards the side with less caster - good on ovals, bad on road courses

    Camber: too much negative
    Inside of tyre excessively hot and/or wearing too rapidly. At the front this will show up as reduced braking capability and at the rear as reduced acceleration capability. Depending on the racetrack and the characteristics of the individual tyre, inside temperature should be 10-25 hotter than the outside. Use a real pyrometer with a needle rather than an infra red surface temperature device.

    Camber: not enough negative
    Outside of tyre will be hot and wearing. This should never be and is almost always caused by running static positive camber at the rear in an effort to avoid the generation of excessive negative camber under the influence of aero download at high speed.
    - A better solution is improved geometry and increased spring rate. Dynamic positive camber will always degrade rear tyre performance and if extreme, can cause braking instability and/or corner exit oversteer.

    Bump steer, front: too much toe-in in bump
    Car darts over bumps and understeers on corner entry

    Bump steer, front: too much toe-out in bump
    Car wanders under brakes and may dart over one wheel or diagonal bumps
    Car may understeer after initial turn in

    Bump steer, rear: too much toe-in in bump (same as solid axle steer on outside wheel)
    Roll understeer on corner entry
    Mid phase corner understeer
    "Tiptoe" instability when trail braking
    Darting on power application on corner exit

    Bump steer, rear: too much toe-out in bump (same as solid axle steer on outside wheel)
    Instability on acceleration
    Good turn in followed by a tendency to oversteer at mid-phase and exit

    TYRES

    Too much tyre pressure
    Harsh ride, excessive wheel patter, sliding and wheel-spin
    High temperature reading and wear at the centre of the tyre

    Too little tyre pressure
    Soft and mushy response
    Reduced footprint area and reduced traction
    High temperatures with a dip in the centre of the tread

    Front tyres "going off"
    Gradually increasing understeer - Enter corners slower, get on power earlier with less steering lock

    Rear tyres "going off"
    Gradually increasing power on oversteer - Try to carry more speed through corner and be later and more gradual with power application

    LIMITED SLIP MALADIES

    Limited slip differential wearing out
    Initial symptoms are decreased power on understeer or increased power on oversteer and inside wheel spin. The car might be easier to drive, but it will be slow
    - When wear becomes extreme, stability under hard acceleration from low speed will diminish and things will not be pleasant at all

    Excessive cam or ramp angle on coast side plate (clutch pack) limited slip differential
    Corner entry, mid-phase and corner exit understeer. Incurable with geometry changes or rates - must change differential ramps. In 1998, virtually everyone is running 0/0 or 80/80 ramps.

    SUSPENSION GEOMETRY

    Excessive front scrub radius (steering offset)
    Excessive steering effort accompanied by imprecise and inconsistent "feel" and feedback

    Excessive roll centre lateral envelope: front or rear
    Non-linear response and feel to steering input and lateral "G" (side force) generation

    Rear roll centre too low (or front r/c relatively too high)
    Roll axis too far out of parallel with mass centroid axis, leading to non-linear generation of lateral load transfer and chassis roll as well as the generation of excessive front jacking force.
    Tendency will be towards understeer

    Rear roll centre too high (or front r/c relatively too low)
    Opposite of above, tending towards excessive jacking at the rear and oversteer

    Front track width too narrow relative to rear
    Car tends to "trip over its front feet" during slow and medium speed corner entry, evidenced by lots of understeer (remember trying to turn your tricycle?)
    - Crutch is to increase front ride rate and roll resistance and increase the camber curves in the direction of more negative camber in bump (usually by raising the front roll centre)

    INSTABILITY

    Straight line instability: general
    Rear wheel toe-out, either static due to incorrect (or backwards) setting, or dynamic due to bump steer or deflection steer
    Vast lack of rear download or overwhelming preponderance of front download
    Wild amount of front toe-in or toe-out
    Loose or broken chassis, suspension member or suspension link mounting point
    Dead shock absorber

    Straight line instability: under hard acceleration
    Malfunctioning limited slip differential
    Insufficient rear toe-in
    Deflection steer from rear chassis/suspension member or mounting point
    Rear tyre stagger (car pulls to one side)
    Dead rear shock absorber
    Wildly uneven corner weights

    Straight line instability: car darts over bumps (especially one wheel bumps)
    Excessive Ackermann steering geometry
    Excessive front toe-in or toe-out
    Uneven front caster or trail settings
    Insufficient rear wheel droop travel
    Dead shock or uneven shock forces or incorrectly adjusted packers/bump rubbers
    Wildly uneven corner weights
    Front anti-roll bar miles too stiff

    Instability under hard braking: front end wanders
    Excessive front brake bias or uneven corner weights or excessive front damper rebound force

    Instability under hard braking: car wants to spin
    Excessive rear brake bias
    Insufficient rear droop travel
    Wildly uneven corner weights
    Excessive rear damper rebound force
    Unbalanced ride/roll resistance - too much at rear
    Insufficient rear camber (usually in combination with one or more of the above)

    RESPONSE

    Car feels generally too heavy and unresponsive
    Tyre pressures too low
    Insufficient ride and/or roll resistance (springs and bars)
    Excessive aerodynamic download, or insufficient spring for the amount of download
    - If high speed acceleration is sluggish, the culprit is often too large a rear wing Gurney lip

    Car feels sloppy, is slow to take a set in corners, rolls a lot, doesn't want to change direction
    Insufficient tyre pressure
    Insufficient damper forces
    Car too soft in ride and/or roll

    Car responds too quickly "has little feel" slides at the slightest provocation
    Excessive tyre pressure
    Excessive bump force in shock absorbers
    Car too stiff for inexperienced driver
    Excessive ride or roll resistance
    Excessive front or rear toe-in
    Insufficient aerodynamic download

    UNDERSTEER

    Corner entry understeer: car initially points in and then washes out
    Excessive toe-in or toe-out (car is usually "darty")
    Insufficient front droop travel (non droop limited cars only)
    Incorrectly adjusted packers (car rolls on to packers)
    Insufficient front damper bump resistance (similar to roll stiffness example)
    Insufficient front roll stiffness - car may feel like it is pointing in but may actually be falling over onto the outside front tyre due to insufficient front roll stiffness or diagonal load transfer under heavy trail braking. Initial understeer can often be cured by increasing front roll resistance, even though doing so may increase the amount of lateral load transfer.
    Non linear lateral load transfer due to spring and/or bar geometry. Or to non-optimal roll axis inclination

    Corner entry understeer: car won't point in and gets progressively worse
    Driver braking too hard, too late
    Relatively narrow front track width
    Excessive front tyre pressure
    Excessive front roll stiffness (spring or bar)
    Relative lack of front download (excessive rear download)
    Incorrectly adjusted packers or bump rubbers (car rolls onto packers)
    Insufficient front toe-in
    Insufficient Ackermann effect in steering geometry
    Front roll centre too high or too low
    Insufficient front damper bump force
    Insufficient front toe-out
    Insufficient front wheel droop travel (on non droop limited cars only)
    Nose being "sucked down" due to ground effect
    Excessive Ackermann steering geometry
    Can also be caused by unloading the front tyres due to rearward load transfer under acceleration - cures include:
    - Increasing front damper rebound force
    - Increasing rear damper low speed damper rebound force
    - Increasing rear anti-squat
    - Droop limiting front suspension (will also make turn in more positive and will reduce overall understeer)

    Mid-corner (mid-phase) understeer
    Excessive front tyre pressure
    Excessive relative front roll stiffness
    Excessive front toe (in or out)
    Excessive Ackermann steering geometry
    Insufficient front dynamic camber
    Relatively narrow front track width
    Insufficient front wheel travel (car rolls onto packers or bottomed shock)
    Insufficient droop travel (on non droop limited cars)

    Corner exit understeer: slow corners
    Often a function of excessive corner entry and mid-phase understeer (whether driver induced or car induced) followed by throttle application whilst maintaining the understeer steering lock. The first step must be to cure the corner entry and mid-phase understeer. If this is impractical, then corner entry speed should be reduced slightly in order to allow earlier throttle application. Sometimes we have to be patient.

    Corner exit understeer: fast corners
    Relative lack of front download - often caused by negative pitch angle (squat) due to rearward load transfer on acceleration. Can be helped by increasing rear anti-squat and/or by increasing rear low speed bump force, increasing front droop force and by limiting the front suspension droop travel.
    Relatively narrow front track width
    Excessive ramp angle or pre-load on clutch pack or plate type limited slip differentials.

    Understeer stronger in one direction than in the other
    Uneven corner weights
    Uneven caster
    Uneven camber (especially front)

    OVERSTEER

    Corner Entry Oversteer
    Excessively heavy trail braking
    Excessive rearward brake bias
    Severe rearward ride rate/roll resistance imbalance
    Rear roll centre too high
    Diabolical lack of rear download
    Severely limited rear droop travel
    Broken or non-functioning outside rear damper
    Broken or non-functioning front anti-roll bar

    Note: A slight feeling of rear "tiptoe" type hunting on corner entry can be due to excessive rear toe-in or excessive rear damper rebound force.

    Mid-corner (mid-phase) oversteer
    Driver threw the car at the corner to get through initial understeer - only cure is to educate the driver and/or decrease understeer
    Excessive rear tyre pressure
    Excessive relative rear ride and/or roll stiffness
    Rear suspension bottoming in roll
    Insufficient rear droop travel (non droop limited cars only)
    Very loose rear anti-roll bar linkage

    Corner exit oversteer: gets progressively worse from the time the power is applied
    Worn out limited slip differential
    Excessive anti-squat geometry
    Excessive rear ride and/or roll stiffness
    Insufficient rear spring, bar or shock (low piston speed bump force) allowing the car to "fall over" onto outside rear tyre
    Excessive rear negative camber
    Too little dynamic rear toe-in
    Relatively insufficient rear download

    Note: If car feels as though it is sliding through the corner rather than rolling freely, reduce the rear toe-in and see what happens.

    Corner exit oversteer "sudden" - car seems to take a normal exit set and then breaks loose
    Insufficient rear suspension travel (lifting the inside wheel on non droop limited cars or bottoming the outside suspension due to lack of bump travel)
    Incorrectly adjusted packers
    Dead rear damper
    Sudden change in outside rear tyre camber
    Too much throttle applied too soon - often after the drivers confidence has been boosted by the car taking a set.

    Car does not put the power down smoothly on the exit of smooth corners
    Worn out limited slip differential
    Excessive rear ride/roll resistance
    Excessive anti-squat geometry
    Excessive rear tyre pressure
    Tyres gone
    Excessive rear damper low piston speed bump force
    Excessive rear dynamic camber - either from download or from camber change on squat
    Relative lack of rear download

    Car does not put the power down on the exit of bumpy corners
    Any or all of the above for smooth corners
    Excessive rear damper high piston speed force
    Excessive rear damper rebound force (jacking down)
    Insufficient rear droop travel

    TRANSITIONS

    Understeer in, snap to oversteer on power application
    The most common complaint of all! Usually caused by too little roll resistance - car falls over on entry and then snaps.
    - Increase front bar and/or spring and/or front damper low piston speed bump force. Stiffening the bar will also transfer some load on to the inside rear tyre on acceleration.
    - If the suggestion above cures the understeer but the car still snaps, the culprit is almost always the car falling over on the outside rear tyre on longitudinal plus lateral load transfer. Add rear bar or spring. Bar will transfer load away from the inside rear tyre. Spring will not. Spring will, however, decrease traction over exit bumps while bar will not.
    Loose anti-roll bar linkage/blade sockets can have the exactly same effect

    Car is slow to change directions in chicanes or esses
    Insufficient ride/roll stiffness, especially at front.
    Relatively narrow front track width.
    Insufficient front damper low piston speed bump force.

    BRAKES

    Brake pedal gets soft, spongy and/or long during session or race
    Fluid boiling in calipers. Not pad fade! Upgrade fluid and/or cool calipers.

    Brake pedal is soft, spongy and/or long before the car is run
    Air in the system - bleed brakes.
    Brake pads badly taper worn - replace

    Reduced stopping power with normal brake pedal
    Pad fade - due either to unbedded new pads or to temperature beyond pad capacity. Upgrade pads.

    Long pedal with little effort required
    Master cylinder(s) too small or pedal mechanical advantage too great.

    Rough braking - pedal vibrates under pressure
    Organic pickup on discs - clean discs with garnet paper (not aluminium oxide sandpaper) and upgrade pads
    Warped (not grooved) rotors. Grind (or, if you must, turn) rotor surfaces
    Insufficient axial float on floating discs

    Uneven braking - car pulls to one side
    Stuck piston(s) - rebuild calipers

    Brake bias changes during application
    Excessive clearance between master cylinder push rod clevises and bias bar bearing housing.
    Rod end bearings used instead of clevises on master cylinder push rods.
    Bias bar incorrectly adjusted. Bar must be perpendicular to vehicle longitudinal axis with full foot pressure applied. Contrary to popular opinion, relative length of master cylinder pushrods is immaterial.

  2. #2
    HJC Non Paid Member
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    Default

    Brilliant bit of info Spam

    for those that didn't read it completly you just drop it on its arse!!

  3. #3

    Default

    Quote Originally Posted by markturbo View Post
    Brilliant bit of info Spam

    for those that didn't read it completly you just drop it on its arse!!





    Rofl

    great little article that, worth consulting if one is trying to iron out certain handling traits

  4. #4
    HJC Non Paid Member
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    Default

    Nice.
    Bookmarked!

  5. #5
    Super Moderator
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    Default

    Not much to take in there then, I prefer Mark's summary.

    Good find.

  6. #6
    HJC Non Paid Member
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    Default Re: Car setup - cause and effect

    Quote Originally Posted by Revo View Post




    Rofl

    great little article that, worth consulting if one is trying to iron out certain handling traits
    Hi Revo,
    Great find, some interesting info there.The effects of the automobile on everyday life have been a subject of controversy.

    Thanks.

    ___________________________________________

    phantom hire | rolls royce phantom hire



  7. #7
    HJC Paid Member
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    Default

    This is a post from April '09!!! And what is with the link to RR hire?

  8. #8
    HJC Non Paid Member
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    Default

    Quote Originally Posted by choness2004 View Post
    This is a post from April '09!!! And what is with the link to RR hire?
    What he said ^^^^^^

    But still good info though....

  9. #9
    HJC Non Paid Member
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    Default Re: Car setup - cause and effect

    wish i could be so creaative with my posts

  10. #10
    Super Moderator (formerly bananayellow)
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    Default Re: Car setup - cause and effect

    Whoa thread revival!

    No advertising allowed though I'm afraid.

 

 

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