Car Setup: Vehicle Dynamics - Cause And Effect Guide

Published: June 23, 2017

Acknowledgment: this page was mirrored from Trackpedia.

This information can help drivers and mechanics to accurately link the behavior or "feel" of a race car to specific components of the car's suspension and braking systems, or to the driver themselves.

Furthermore, it can be used to confirm that changes to the car being considered will have not only the desired effect, but will not create unwanted side-effects.

Ride And Roll Resistance

Springs

Too much spring: overall

Relatively too much spring: front

Relatively too much spring: rear

Too little spring: overall

Relatively too little spring: rear

Anti-Roll Bars

Too much anti-roll bar: overall

Relatively too much anti-roll bar: front

Relatively too much anti-roll bar: rear

Too little anti-roll bar: overall

Relatively too little anti-roll bar: front

Relatively too little anti-roll: rear

[The author's] 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 tire to the laden tire — exactly what we don't want at the rear. [He] 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

Too much rebound force

Too much bump force: general

Too much low piston speed bump force

Too much high piston speed bump force

Too little shock: overall

Too little rebound force: overall

Too little bump force: overall

Too little low piston speed bump force

Too little high piston speed bump force

Dead shock on one corner

Wheel Alignment

Front toe-in: too much

Front toe-out: too much

Rear toe-in: too little

Rear toe-in: too much

Rear toe-out: any

Front wheel caster or trail: too little

Front wheel caster or trail: too much

Front wheel caster or trail: uneven

Camber: too much negative

Camber: not enough negative

Bump steer, front: too much toe-in in bump

Bump steer, front: too much toe-out in bump

Bump steer, rear: too much toe-in in bump (same as solid axle steer on outside wheel)

Bump steer, rear: too much toe-out in bump (same as solid axle steer on outside wheel)

Tires

Too much tire pressure

Too little tire pressure

Front tires "going off"

Rear tires "going off"

Suspension Geometry

Excessive front scrub radius (steering offset)

Excessive roll centre lateral envelope: front or rear

Rear roll centre too low (or front r/c relatively too high)

Rear roll centre too high (or front r/c relatively too low)

Front track width too narrow relative to rear

Handling

Instability

Straight line instability: general

Straight line instability: under hard acceleration

Straight line instability: car darts over bumps (especially one wheel bumps)

Instability under hard braking: front end wanders

Instability under hard braking: car wants to spin

Response

Car feels generally too heavy and unresponsive

Car feels sloppy, is slow to take a set in corners, rolls a lot, doesn't want to change direction

Car responds too quickly — has little feel — slides at the slightest provocation

Understeer

Corner entry understeer: car initially points in and then washes out

Corner entry understeer: car won't point in and gets progressively worse

Mid-corner (mid-phase) understeer

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

Understeer stronger in one direction than in the other

Oversteer

Corner Entry Oversteer

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

Corner exit oversteer: gets progressively worse from the time the power is applied

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

Car does not put the power down smoothly on the exit of smooth corners

Car does not put the power down on the exit of bumpy corners

Transitions

Understeer in, snap to oversteer on power application

Car is slow to change directions in chicanes or esses

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

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

Uneven braking — car pulls to one side

Brake bias changes during application

Limited Slip Maladies

Limited slip differential wearing out

Excessive cam or ramp angle on coast side plate (clutch pack) limited slip differential