Alignment

Why ensure 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