Wheel Alignment

CASTER

Effects of Caster High Positive Caster increases ( + )

– Straight ahead stability

– Steering effort required is high

– Steering wheel return to center

– Road Shock felt from bumps

More Negative Caster ( -- )– No Straight ahead stability

– Steering effort is light

– Wheel not returning to center

– Smooth ride, little road shock

Uneven Caster will cause the vehicle to pull towards the side with less Caster (more Negative -)

½ degree or moreNot a tire wearing angle!!!!

Caster can be set unevenly to counter act for road crown pull.

Usually ½ degree or more on the downhill side.

Caster trail is the distance between the caster line and the tire point of contact.

CAMBER

Camber = The inward or out ward tilt of the centerline of the

tire.

Camber

The more camber you have, the more the load is placed on the outside of the tire.

Excessive positive or negative camber can cause tire wear on the edges

Camber can cause a car to pull to one side

Effects of Camber Tire wearing angle Directional control angle

– Pull towards the side with more positive camber

Excessive Camber Accelerates bearing wear– Load is not evenly set on bearings.

– Positive wears the inner bearing

– Negative wears the outer bearing

Influences on Camber Uneven Loading Body roll during turns Road Crown Rough road Surfaces Suspension Wear Suspension Damage Tire size Caster

Faster cornering wears out edges of tires!!!!

Camber can be set unevenly to counter act for road crown pull.

Cross Camber should never exceed ½ degree

Camber will pull to the most positive side Camber Roll

– Caster angle may produce a change in the camber angle when the wheels are turned

Camber is adjustable on most vehicles

Toe in Toe outToe

Darting

Darting

Wanter

Toe

Toe in = Darting

Toe out = Wander

Effects of Toe Tire wear

– Scuffing sideways • Scuffing is Drag and hop!

– Wear tends to be the same on both tires, unlike Camber wear Directional control angle Can cause shimmy! Diagonal Wipe on the rear tires if toe is excessive

– Lots of rotations! Toe Change can occur as suspension travels up and down.

– Measure toe change at 1 inch increments– Should be no change!– Check length and height of tie rods!!!

City driving can cause unusual tire wear that might be blamed on Toe problems!!

SAISteering Axis Inclination

SAI

The inward tilt at the top of the strut.

(looking from the front)(looking from the front)

SAI

The inward tilt at the top of the strut.(looking from the front)(looking from the front)

SAI and Included angle

Include angle = SAI + pos.

camber

Effects of SAI

Ensures Steering stability– FWD use more SAI because of small Caster

Helps with Steering Wheel returnability– Uses Gravity to assist

Diagnosis with SAISLA & Strut/SLA

SAI Camber Included Angle

Diagnosis

Correct < spec < spec Bent steering Knuckle

< Spec > Spec Correct Bent lower control arm

< Spec > Spec > Spec Bent lower arm & Knuckle or spindle

> Spec < spec Correct Bent upper control arm

Diagnosis with SAI Strut Suspensions

SAI Camber IA Diagnosis

Correct < spec < spec Bent spindle or strut

Correct > Spec > Spec Bent spindle or strut

< spec > Spec Correct Bent control arm or strut

< spec

< spec

>Spec

< spec

> Spec

< spec

Bent control arm or strut or spindle.

strut tower out at top

strut tower in at top

> Spec < spec correct Strut tower in at top

> Spec > Spec > Spec Strut tower in at top

And bent spindle & strut

0 bump steer No toe angle change.

– Need to Check for this at 1 inch increments 3 factors affect bump steer

– Tie rod length– Relative heights of inner and outer tie rod ends– Steering arm length

Zero SAI would = Major bump steer

Positive Scrub Radius

Positive scrub radius

RWD vehiclesSport cars

Feel the steering wheel tug when braking

Road feelDriver Involvement

needed

Negative Scrub radius

Used on

Split diagonal braking systems

Self Correcting when braking

No driver involvement needed

No road feel

Effects of: Larger tire smaller tire deep dish

wheel

Larger Scrub = harder to turn and increased wear

Smaller Scrub = easy turns

Braking stability - Negative has greater directional stability

Positive decreases braking stability (aftermarket rims)

Turning Angle, Setback,Thrust Angle.

Turning Angle

Setback

Thrust

The End