wheel alignment and significance
TRANSCRIPT
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Wheel Alignment
CASTER
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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!!!!
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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.
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CAMBER
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Camber = The inward or out ward tilt of the centerline of the
tire.
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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
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Camber can cause a car to pull to one side
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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
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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!!!!
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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
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Camber is adjustable on most vehicles
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Toe in Toe outToe
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Darting
Darting
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Wanter
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Toe
Toe in = Darting
Toe out = Wander
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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!!
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SAISteering Axis Inclination
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SAI
The inward tilt at the top of the strut.
(looking from the front)(looking from the front)
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SAI
The inward tilt at the top of the strut.(looking from the front)(looking from the front)
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SAI and Included angle
Include angle = SAI + pos.
camber
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Effects of SAI
Ensures Steering stability– FWD use more SAI because of small Caster
Helps with Steering Wheel returnability– Uses Gravity to assist
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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
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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
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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
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Positive Scrub Radius
Positive scrub radius
RWD vehiclesSport cars
Feel the steering wheel tug when braking
Road feelDriver Involvement
needed
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Negative Scrub radius
Used on
Split diagonal braking systems
Self Correcting when braking
No driver involvement needed
No road feel
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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)
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Turning Angle, Setback,Thrust Angle.
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Turning Angle
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Setback
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Thrust
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The End