Wheel Alignment Basics

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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

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