Alignment

Why alignment?

1. To eliminate tire wear

2. To give vehicle proper handling– Eliminate pull, drift, wander, stiff steering

and poor steering return ability

Three types of alignments

Geometric centerline (2 wheel) (POOR)– Aligns front wheels to center of vehicle

Thrust angle (2 wheel) (GOOD)– Aligns front wheels to thrust angle

Total alignment (4 wheel) (BEST)– Aligns all 4 wheels to geometric centerline– Not possible on all vehicles

Before alignment

Always check steering and suspension components for wear– Including wheel bearings

Always check tire pressure– A low tire may cause pull

Always check tire condition– Tire wear will indicate possible problems

Try to duplicate the complaint if possible

Camber Inward or outward tilt of the top of the tire Outward tip is positive / Inward tip is

negative If excessive (about 1 1/4 degree off)

positive or negative, camber will cause tire wear

May cause pull to most positive side Maximum cross camber usually .5deg

Caster Forward or rearward tilt of the steering

axis Forward is negative \ rearward is positive Positive gives steering stability and

returnability Negative decreases turning effort May cause pull to most negative side Maximum cross caster usually .5deg

Camber roll

Toe

Difference between the front and rear of the tires

Toe in or positive toe means the front of the tires are closer than the rear of the tires

Toe out or negative toe means the rear of the tires are closer than the front of the tires

Toe

Excessive toe in (positive) will cause wear on the outer tire edges

Excessive toe out (negative) will cause wear on the inner tire edges

Incorrect toe is THE most common cause of tire wear

Different toe side to side will cause steering wheel to be off center but will not cause pull

Camber and caster adjustments

If adjustments are possible, it will usually be at only one pivot point

Camber and caster are often adjusted together

Slotted holes

Common on MacPherson strut with 2 bolts at knuckle

Common at top of strut mount

Eccentrics SLA may have 2

eccentrics on upper control arm bolts

MacPherson strut may have eccentric at knuckle attaching bolts

Depending on design, may be used to adjust both angles or just camber

Shims

Found mostly on vehicles with SLA suspensions

Shims come in various thickness'

Can adjust both caster and camber

Strut rod

Lengthening or shorting strut rod attached to lower control will change caster

Cradle adjustment

Some vehicles allow cradle adjustment

Can affect both caster and camber

Should only be done if manufacture recommends

Shim practice

Toe adjustment

Always performed as last adjustment Adjusted by effectively lengthening or

shortening tie rods Some vehicles have only one

adjustable tie rod Sometimes toe is only adjustment

possible

Steering axis inclination Included angle

Diagnostic angles

Definitions

SAI a line drawn through the steering axis, as viewed from the front

SAI allows smaller camber angles but keeps load on inboard of spindle

SAI moves spindle in arc like caster Included angle is the total of SAI +

camber

SAI and IA Both angles are used for diagnostics when

bent or loose components are suspect Many vehicles do not give specs Side to side differences most important 1.5 deg diff side to side or off of specs

maximum allowed Should be checked whenever camber is

found to be way off

Cradle adjusting If SAI off opposite

amounts side to side suspect cradle alignment

Rear Wheel Alignment

Rear wheels

Usually only front wheel drive vehicles Purpose is to realign thrust angle and

geometric centerline Camber and toe only angles Rear toe or camber problems can

cause lead, pull, dog tracking, tire wear

Adjusting rear wheels

Camber adjusted first if available Toe adjustment more common than

camber

Common adjustments

Rear toe

Can be adjusted by tie rods similar to front

Rear toe and camber

Can be adjusted using eccentrics, depending on their position, similar to front end

Aftermarket shims

Full contact shims can adjust both angles

Shim example

The End