1 introduction to wheel alignment. 2 when is an alignment necessary whenever components in the...
TRANSCRIPT
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Introduction to wheel
alignment
Introduction to wheel
alignment
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When is an alignment necessaryWhen is an alignment necessary
• Whenever components in the suspension system have been removed and replaced.– Strut replacement– Ball joint replacement– Steering rack or tie rod replacement– etc
• Anytime components that effect alignment are disconnected and reconnected.– When the sub-frame is removed during a
transmission overhaul the bolts connecting the sub-frame may be in a slightly different position on reassembly.
• Whenever components in the suspension system have been removed and replaced.– Strut replacement– Ball joint replacement– Steering rack or tie rod replacement– etc
• Anytime components that effect alignment are disconnected and reconnected.– When the sub-frame is removed during a
transmission overhaul the bolts connecting the sub-frame may be in a slightly different position on reassembly.
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When is an alignment necessaryWhen is an alignment necessary
• When the vehicle pulls to either side and the tires and brakes appear to be normal.– If there is a large difference - left to right - in
Caster, Camber or Steering Axis Inclination.
• When there is uneven tire wear.– Excess toe-in or toe-out causes wear on the
edges of both tires.– Excess camber [positive and negative] cause
edge wear on the wheel with the excess camber.
• When the vehicle pulls to either side and the tires and brakes appear to be normal.– If there is a large difference - left to right - in
Caster, Camber or Steering Axis Inclination.
• When there is uneven tire wear.– Excess toe-in or toe-out causes wear on the
edges of both tires.– Excess camber [positive and negative] cause
edge wear on the wheel with the excess camber.
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Tire wear - excess camberTire wear - excess camber
• When the tires have excess camber most of the weight applied to the tire is placed on one edge of the tire.
• When the tires have excess camber most of the weight applied to the tire is placed on one edge of the tire.
Weight is concentrated on one
side of the tire
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Tire wear – excess toe-inTire wear – excess toe-in
• When the is excessive toe-in the outboard side of both front tires wears prematurely.
• Excess toe-out causes the opposite condition – premature wear on the inboard side of both tires.
• When the is excessive toe-in the outboard side of both front tires wears prematurely.
• Excess toe-out causes the opposite condition – premature wear on the inboard side of both tires.
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Tire wear caused by excess toe outTire wear caused by excess toe out
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When is an alignment necessaryWhen is an alignment necessary
• Steering wheel not centered.– Un-centered steering [Steering wheel not at 12
O’clock] is a result of uneven – left-to-right - toe angles.
– To center the steering the toe angle must be adjusted to the thrust line of the vehicle.
• Steering wheel not centered.– Un-centered steering [Steering wheel not at 12
O’clock] is a result of uneven – left-to-right - toe angles.
– To center the steering the toe angle must be adjusted to the thrust line of the vehicle.
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Steering not centeredSteering not centered
• All of the wheels on this vehicle are parallel when the steering wheel is at 12 o’clock except the left front which is toed-out 2o.
• In this condition the vehicle does not pull.
• The only thing the driver notices is that the steering wheel is at 1 o’clock when the car is driven straight ahead.
• All of the wheels on this vehicle are parallel when the steering wheel is at 12 o’clock except the left front which is toed-out 2o.
• In this condition the vehicle does not pull.
• The only thing the driver notices is that the steering wheel is at 1 o’clock when the car is driven straight ahead.
2o toe-out Zero toe
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Steering not centeredSteering not centered
• When the car is driven the driver will turn the steering until the vehicle travels straight.
• The driver doesn’t look at the steering wheel – he looks at the road ahead.
• With one degree of toe-out on each front wheel the car travels straight and does not pull because toe is balanced left to right.
• Driving with this much toe-out will rapidly wear out the front tires.
• When the car is driven the driver will turn the steering until the vehicle travels straight.
• The driver doesn’t look at the steering wheel – he looks at the road ahead.
• With one degree of toe-out on each front wheel the car travels straight and does not pull because toe is balanced left to right.
• Driving with this much toe-out will rapidly wear out the front tires.
1o toe-out 1o toe-out
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Traditional toe measurementTraditional toe measurement
• The traditional method of defining toe was the difference in the distance between the center of the tires at the leading edge and the distance between the center of the tires at the leading edge.
• This dimension is expressed in fractions of an inch and is called ‘total toe’.
• The traditional method of defining toe was the difference in the distance between the center of the tires at the leading edge and the distance between the center of the tires at the leading edge.
• This dimension is expressed in fractions of an inch and is called ‘total toe’.
59 7/8”
59 3/4”
Total toe = 1/8” toe-out
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Vehicle centerlineVehicle centerline
• The vehicle centerline is a line connecting the center point of the front axle with the center point of the rear axle.
• The vehicle centerline is the reference line from which the thrust angle is determined.
• The vehicle centerline is a line connecting the center point of the front axle with the center point of the rear axle.
• The vehicle centerline is the reference line from which the thrust angle is determined.
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Thrust angleThrust angle
• If the toe angles of the front wheels are perfectly straight but the rear wheels are not the steering will not be centered.
• The thrust angle between the center line and a line bisecting [half way between]the two rear toe angles.
• If the toe angles of the front wheels are perfectly straight but the rear wheels are not the steering will not be centered.
• The thrust angle between the center line and a line bisecting [half way between]the two rear toe angles.2o toe-out 4o toe-in
Zero toeZero toe
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line
Th
rust
An
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Ve
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line
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Thrust angleThrust angle
• The thrust angle here will cause the vehicle to turn to the right when the steering wheel is at 12 o’clock.
• The rear toe angles are in effect steering the car to the right.
• The thrust angle here will cause the vehicle to turn to the right when the steering wheel is at 12 o’clock.
• The rear toe angles are in effect steering the car to the right.
2o toe-out 4o toe-in
Zero toeZero toe
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line
Th
rust
An
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Thrust angle toe measurementThrust angle toe measurement
• Modern alignment machines measure individual toe in relation to the vehicles thrust angle.
• This is essential to insure that the steering wheel is properly centered after a wheel alignment.
• Modern alignment machines measure individual toe in relation to the vehicles thrust angle.
• This is essential to insure that the steering wheel is properly centered after a wheel alignment.
Ve
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Thr
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An
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Left toe = 1/8” toe-out Right toe = zero
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Four wheel alignmentFour wheel alignment
• If there is rear toe angles exceed the alignment specifications and are adjustable the best procedure is to adjust the rear wheel toe and then adjust the front toe to the new thrust angle.
• If there is rear toe angles exceed the alignment specifications and are adjustable the best procedure is to adjust the rear wheel toe and then adjust the front toe to the new thrust angle.
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Thr
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Left toe = 1/16” toe-in
Right toe = 1/16” toe-in
Left rear toe = 1/16” toe-in
Right rear toe = zero
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Thrust angle alignmentThrust angle alignment
• If the rear toe is not adjustable or if the customer does not want to pay for the extra labor in adjusting the rear toe the front toe is adjusted to the thrust angle.
• If the rear toe is not adjustable or if the customer does not want to pay for the extra labor in adjusting the rear toe the front toe is adjusted to the thrust angle.
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Thr
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Left toe = 1/16” toe-in
Right toe = 1/16” toe-in
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Camber angleCamber angle
• Camber is the angle formed between the centerline of the tire and true vertical.
• Camber is expressed in degrees.
• Camber can be measured directly from the tire.
• Camber is positive when the centerline at the top of the tire is outboard the centerline at the bottom.
• Camber is the angle formed between the centerline of the tire and true vertical.
• Camber is expressed in degrees.
• Camber can be measured directly from the tire.
• Camber is positive when the centerline at the top of the tire is outboard the centerline at the bottom.
Camber = + 1.5o
VerticalTire
center line
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Camber angleCamber angle
• Camber is negative when center line at the top of the tire is inboard the center line at the bottom.
• Excessive camber causes tire wear.
• Unequal camber side-to-side will cause a car to pull to the side with the highest positive camber.
• Camber is negative when center line at the top of the tire is inboard the center line at the bottom.
• Excessive camber causes tire wear.
• Unequal camber side-to-side will cause a car to pull to the side with the highest positive camber.
Camber = - 2.3o
VerticalTire
center line
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Fractions of a degreeFractions of a degree
• There are three ways of expressing fractional degrees.– True fractions ………….. example +1 3/4
o
– Decimal notation …....… example +1.7 o
– Degrees-Hours-minutes … example + 1o, 45’
• Alignment machines normally use decimal degrees but you may encounter the other two methods in shop manuals
• There are three ways of expressing fractional degrees.– True fractions ………….. example +1 3/4
o
– Decimal notation …....… example +1.7 o
– Degrees-Hours-minutes … example + 1o, 45’
• Alignment machines normally use decimal degrees but you may encounter the other two methods in shop manuals
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Steering Axis Inclination [SAI]Steering Axis Inclination [SAI]
• The steering axis is a line connecting the upper and lower ball joints or the strut bearing and ball joint on a MacPherson strut suspension.
• SAI is the angle between the steering axis and true vertical.
• The steering axis is a line connecting the upper and lower ball joints or the strut bearing and ball joint on a MacPherson strut suspension.
• SAI is the angle between the steering axis and true vertical.
VerticalSAISteering axis
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SAI measurementSAI measurement
• SAI is a hidden angle. It cannot be measured directly.
• SAI is measured during a caster sweep as the wheels are steered through a 20
o angle.
• During the caster sweep procedure the alignment machine measures the change in tire angle as it turns 10
o left to 10
o right.
• The higher the SAI the greater this change will be. • The front brakes must be locked during the sweep
otherwise the measurement is invalid
• SAI is a hidden angle. It cannot be measured directly.
• SAI is measured during a caster sweep as the wheels are steered through a 20
o angle.
• During the caster sweep procedure the alignment machine measures the change in tire angle as it turns 10
o left to 10
o right.
• The higher the SAI the greater this change will be. • The front brakes must be locked during the sweep
otherwise the measurement is invalid
10o Right 10
o LeftStraight ahead
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Function of SAIFunction of SAI
• SAI provides steering returnability.• Returnability is the tendency of the steering
to return to the straight ahead position after the turn has been completed with little driver effort.
• Positive SAI causes the front end of the car to rise slightly as the steering is turned away from straight ahead.
• SAI provides steering returnability.• Returnability is the tendency of the steering
to return to the straight ahead position after the turn has been completed with little driver effort.
• Positive SAI causes the front end of the car to rise slightly as the steering is turned away from straight ahead.
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SAISAI
• Gravity provides the force to return the steering to straight ahead.
• The down side of SAI is that it makes the car harder to steer since you are lifting the front end up a fraction of an inch each time you turn left or right.
• Uneven left-to-right SAI will cause a pull to the side with the lowest positive SAI.
• SAI is not usually adjustable. It is measured primarily for diagnostic purposes.
• Gravity provides the force to return the steering to straight ahead.
• The down side of SAI is that it makes the car harder to steer since you are lifting the front end up a fraction of an inch each time you turn left or right.
• Uneven left-to-right SAI will cause a pull to the side with the lowest positive SAI.
• SAI is not usually adjustable. It is measured primarily for diagnostic purposes.
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Included angleIncluded angle
• Included angle is the combination of SAI and Camber.
• If SAI is +6o and
Camber is +1.5o the
included angle is 7.5o.
• If SAI is +6o and
Camber is - 0.5o the
included angle is 5.5o
• Included angle is the combination of SAI and Camber.
• If SAI is +6o and
Camber is +1.5o the
included angle is 7.5o.
• If SAI is +6o and
Camber is - 0.5o the
included angle is 5.5o
Camber angle
IASteering axis
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Included angleIncluded angle
• When camber is negative it’s value is subtracted from SAI to calculate included angle.
• Like SAI, Include Angle is measured for diagnostic purposes
• When camber is negative it’s value is subtracted from SAI to calculate included angle.
• Like SAI, Include Angle is measured for diagnostic purposes
Camber angle
IASteering axis
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CasterCaster
• Caster is the forward or rearward tilt of the steering axis as measured from vertical.
• Reward tilt is Positive caster, forward tilt is negative.
• Caster is the forward or rearward tilt of the steering axis as measured from vertical.
• Reward tilt is Positive caster, forward tilt is negative.
Vertical Steering axis
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CasterCaster
• Positive caster provides steering stability and returnability.
• Positive caster allows the driver to momentarily take his hands off the wheel without having the car swerve into oncoming traffic.
• Excess caster however may make the car harder to steer.
• Positive caster provides steering stability and returnability.
• Positive caster allows the driver to momentarily take his hands off the wheel without having the car swerve into oncoming traffic.
• Excess caster however may make the car harder to steer.
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Caster Caster
• Caster is based on the positioning of the ball joints.
• If the upper ball joint is moved rearward the caster becomes more positive.
• When the lower ball joint is moved rearward the caster becomes less positive.
• Caster is based on the positioning of the ball joints.
• If the upper ball joint is moved rearward the caster becomes more positive.
• When the lower ball joint is moved rearward the caster becomes less positive.
Vertical Steering axis
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CasterCaster
• Excessive caster does not cause tire wear.• Uneven caster [side-to-side] will cause a
pull. • The vehicle will pull to the side with the
lowest positive caster.• Like SAI, caster is a hidden angle. It cannot
be measured directly from the tire.• Caster is measured by monitoring the
change in camber angle during a caster sweep.
• Excessive caster does not cause tire wear.• Uneven caster [side-to-side] will cause a
pull. • The vehicle will pull to the side with the
lowest positive caster.• Like SAI, caster is a hidden angle. It cannot
be measured directly from the tire.• Caster is measured by monitoring the
change in camber angle during a caster sweep.
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Caster sweepCaster sweep
• A caster sweep is a procedure done on an alignment machine to measure caster.
• During the sweep the turn-plates are unlocked and the front brakes are locked using a brake pedal depressor.
• The wheel to be measured is turned inward 10
o and the camber
angle is recorded.• The wheel is then turned outward
10o and a second camber
measurement is made.• The difference between the two
camber readings is used to calculate caster.
• A caster sweep is a procedure done on an alignment machine to measure caster.
• During the sweep the turn-plates are unlocked and the front brakes are locked using a brake pedal depressor.
• The wheel to be measured is turned inward 10
o and the camber
angle is recorded.• The wheel is then turned outward
10o and a second camber
measurement is made.• The difference between the two
camber readings is used to calculate caster.
10o inward
Camber = -4o
Straight ahead Camber = 0
o
10o Outward
Camber = +4o
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Pre - Alignment
Checks
Pre - Alignment
Checks
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Pre-alignment checkPre-alignment check
• Tire pressure / tire condition– Look for damage and abnormal treadwear
• Tire size– Are all 4 tires the same size
• Vehicle loading – Are there any heavy objects in the vehicle – If the customer always carries a tool box in the
trunk the vehicle should be aligned with the toolbox
– Some manufactures specify that the gas tank should be full
• Tire pressure / tire condition– Look for damage and abnormal treadwear
• Tire size– Are all 4 tires the same size
• Vehicle loading – Are there any heavy objects in the vehicle – If the customer always carries a tool box in the
trunk the vehicle should be aligned with the toolbox
– Some manufactures specify that the gas tank should be full
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Pre-alignment checkPre-alignment check
• Ride height• Steering freeplay• Strut / shock jounce test
– Worn struts/shocks should not effect the alignment– Binding struts/shocks will have a major effect on
alignment– A jounce test is performed by manually pushing
down on a fender then quickly releasing your hands.
– The vehicle should return to the same height without oscillations
– If the fender does not return to it’s original position the strut / shock may be binding
• Ride height• Steering freeplay• Strut / shock jounce test
– Worn struts/shocks should not effect the alignment– Binding struts/shocks will have a major effect on
alignment– A jounce test is performed by manually pushing
down on a fender then quickly releasing your hands.
– The vehicle should return to the same height without oscillations
– If the fender does not return to it’s original position the strut / shock may be binding
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Pre alignment road testPre alignment road test
• During the road test you should be looking for.– Pull to either side– Wander– Steering return– Hard steering– Steering wheel position – Excess freeplay in steering– Turn signal canceling– Noise / vibration– Dive / squat in braking and acceleration– Excess roll during cornering– Excess road shock
• During the road test you should be looking for.– Pull to either side– Wander– Steering return– Hard steering– Steering wheel position – Excess freeplay in steering– Turn signal canceling– Noise / vibration– Dive / squat in braking and acceleration– Excess roll during cornering– Excess road shock
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Pre alignment – undercar /under hood inspectionPre alignment – undercar /under hood inspection
• P/S belt condition and tension• P/S fluid level• Wheel bearing freeplay• Brake drag• Ball joints• Springs• Shocks/struts• Steering linkage • Bushings – control arm and stabilizer bar• Strut mounts
• P/S belt condition and tension• P/S fluid level• Wheel bearing freeplay• Brake drag• Ball joints• Springs• Shocks/struts• Steering linkage • Bushings – control arm and stabilizer bar• Strut mounts