chapter 67 alignment

8/9/2019 Chapter 67 Alignment

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Wheel Alignment

Fundamentals

Chapter 67


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Objectives

Describe each wheel alignment angle

Tell which alignment angles cause wear or pull


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Introduction

Correct wheel alignment allows vehicle to run

straight on the highway Little steering effort

Chapter discusses different alignment angles


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Alignment Angles

Five wheel alignment angles Toe

Camber

Caster Steering axis inclination (SAI)

Turning radius


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Toe (continued)

Causes of incorrect toe Improper adjustment

Looseness in steering linkage due to wear

Collision with a curb Change in caster or camber adjustment

Front toe adjustable on all vehicles Rear toe adjustable on some

Change in toe affects position of the steeringwheel


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Camber

Camber is inward or outward tilt of tire at topAdjustable on most vehicles

Positive camber tire tilts out

Negative camber tire tilts in Inside and outside edges of the tread on

cambered tire have different radii Rotate at different speeds

Camber angle controlled by position of controlarms or struts

Camber roll tire tends to roll in a circle


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Caster

Caster is the angle that describes the forward or

rearward tilt of the spindle support arm

Positive caster top tilted to the rear

Lead point in front of true vertical

Car pulls to side with most negative caster

Too much positive caster results in front wheel

shimmy High amount of wear if car driven on winding

roads, or in city


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Steering Axis Inclination

Amount the spindle support arm leans in at top Not a tire wearing angle

Three functions

After a turn, SAI helps vehicle return to straight SAI keeps vehicle going straight down the roadAllows car to have less positive caster

Included angle combination of SAI and camber

Some cars with large SAI wear outsides of tires SAI can be used as diagnostic angle to

determine if parts are bent


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Scrub Radius

Factor of steering axis inclination

Pivot point for front tires footprint

Distance at the road surface between centerline

of true vertical and steering axis pivot centerline

More scrub radius makes it harder to steer Positive camber reduces scrub radius


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Scrub Radius (continued)

Causes of incorrect scrub radius Lower profile tires and offset wheel rims

Tires and wheels too tall installed on rear-wheel-

drive vehicle Bent front suspension part

Damage to frame at crossmember


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Turning Radius

When turning, outside wheel must travel in wider

arc than inside wheel

Turning radius alignment angle that controls

arc traveledAlso called Ackermann angle

Tires toe out during turn


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Tracking

Wheel base distance between front and rear

tires

Track side-to-side distance between axles

tires

All four wheels should form an exact rectangle

When tracking is off, car tries to steer to the side

Increases tire wear Dog tracking rear axle out of line to the right,

causes steering to be aimed to the right


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Set-Back

Set-back amount that one front wheel is

behind front wheel on other side Measured in degrees

Negative set-back wheel on left side is setback Cause vehicle to steer to left

Cause brake pull

Collision causes incorrect set-back


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Special Handling Characteristics

Slip angle tendency for a tire to continue to goin the direction it was going

Amount of slip angle depends on Tire pressure

Weight exerted vertically on the tire

Wheel alignment setting

Positive camber

Understeer car does not respond to movementof steering wheel during hard turn

Oversteer car turns too far in response to

steering wheel


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chapter 67 alignment

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