Presentation on theme: "Wheel Alignment CASTER. Effects of Caster l High Positive Caster increases ( + ) –Straight ahead stability –Steering effort required is high –Steering."— Presentation transcript:
Wheel Alignment CASTER
Effects of Caster l High Positive Caster increases ( + ) –Straight ahead stability –Steering effort required is high –Steering wheel return to center –Road Shock felt from bumps l 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 more Not a tire wearing angle!!!!
Caster can be set unevenly to counter act for road crown pull. l Usually ½ degree or more on the downhill side. l Caster trail is the distance between the caster line and the tire point of contact.
Camber = The inward or out ward tilt of the centerline of the tire.
Camber l The more camber you have, the more the load is placed on the outside of the tire. l 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 l Tire wearing angle l Directional control angle –Pull towards the side with more positive camber l 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 l Uneven Loading l Body roll during turns l Road Crown l Rough road Surfaces l Suspension Wear l Suspension Damage l Tire size l Caster Faster cornering wears out edges of tires!!!!
Camber can be set unevenly to counter act for road crown pull. l Cross Camber should never exceed ½ degree l Camber will pull to the most positive side l 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 out Toe
Toe l Toe in = Darting l Toe out = Wander
Effects of Toe l Tire wear –Scuffing sideways Scuffing is Drag and hop! –Wear tends to be the same on both tires, unlike Camber wear l Directional control angle l Can cause shimmy! l Diagonal Wipe on the rear tires if toe is excessive –Lots of rotations! l 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!!
SAI Steering Axis Inclination
SAI l The inward tilt at the top of the strut. l (looking from the front)
SAI l The inward tilt at the top of the strut. (looking from the front)
SAI and Included angle l Include angle = l SAI + pos. camber
Effects of SAI l Ensures Steering stability –FWD use more SAI because of small Caster l Helps with Steering Wheel returnability –Uses Gravity to assist
Diagnosis with SAI SLA & Strut/SLA SAICamberIncluded Angle Diagnosis Correct< spec Bent steering Knuckle < Spec> SpecCorrectBent lower control arm < Spec> Spec Bent lower arm & Knuckle or spindle > Spec< specCorrectBent upper control arm
Diagnosis with SAI Strut Suspensions SAICamberIADiagnosis Correct< spec Bent spindle or strut Correct> Spec Bent spindle or strut < spec> SpecCorrectBent control arm or strut < spec >Spec < spec > Spec < spec Bent control arm or strut or spindle. strut tower out at top strut tower in at top > Spec< speccorrectStrut tower in at top > Spec Strut tower in at top And bent spindle & strut
0 bump steer l No toe angle change. –Need to Check for this at 1 inch increments l 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 vehicles Sport cars Feel the steering wheel tug when braking Road feel Driver Involvement needed
Negative Scrub radius Used on Split diagonal braking systems Self Correcting when braking No driver involvement needed No road feel
Effects of: l Larger tire l smaller tire l 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)