Hunter Engineering Winalign Hd Brochure Wheel Alignment Education Guide For Heavy Duty Trucks

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What is Proper Wheel Alignment?

A properly aligned vehicle is one in which all wheels are aimed in the same direction. Some ver y low

tolerance or acceptable error is designed into each vehicle by the manufacturer (see the vehicle

manufacturer specifications).

How Can Wheel Alignment Benefit Your Operation?

The number one and number two operating expenses in over -the-road transportation are fuel and

tires respectively. Both are typically perceived as hard to control. Routine wheel alignment is the

most effective way to control tire costs and can impact fuel costs as well.

Problems created by misalignment:

• Excessive tire wear

•Increased fuel consumption caused by increased rolling resistance

• Unsafe vehicle handling characteristics

• Driver fatigue and driver retention

•Premature suspension component wear

Between 70 and 80 percent of heavy duty vehicles

on the road today are misaligned!

The transportation industry, as a whole, finds that outsourcing timely, accurate alignment service

performed by qualified technicians is difficult to manage. As a result alignment is mostly addressed

after the damage has been done. Simply making alignment par t of a vehicle or fleet preventive

maintenance program allows operators to easily get a handle on this per ceived uncontrollable

expense.

Hunter recommends a minimum of two to three alignments per year or ever y 50,000

to 60,000 miles as part of the average vehicle’ s preventive maintenance program.

Alignment service is a natural fit for ser vice facilities currently repairing suspensions. Technicians

performing repairs on heavy duty suspensions are in ef fect alignment technicians. The only required

equipment is the precision measuring system.

– 1 –

Alignment Angles and Effects

Tire Wear Due to Improper Toe Settings

Toe is the most critical alignment setting for steer axle tire wear . It is measured in inches, millimeters or degrees.

Total Toe is the angle formed by two horizontal

lines through the planes of two wheels. Toe-in is

when the horizontal lines intersect in front of the

vehicle; Toe-out is when the horizontal lines

intersect behind the wheels.

Individual Toe is the angle drawn by a line

drawn through a plane of one wheel r eferenced

to the thrust line of the vehicle. Toe-in is when

the horizontal lines intersect in front of the

wheel. Toe-out is when the lines intersect

behind the wheel.

Excessive toe-out wears the inside of the tire.

Results of excessive toe is wear on the

leading edge of the tire.

+–

+–

Toe-in Toe-out

Toe-out

Toe-in Toe-out

Toe-in

Excessive toe-in wears the outside of the tir e.

– 2 –

Tire Wear Due to Improper

Camber Settings

Camber is the angle formed by the inward or

outward tilt of the wheel referenced to a ver tical

line. This angle is measured in degrees.

Camber is positive when the wheel is tilted

outward at the top and is negative when the

wheel is tilted inward at the top.

Tire wear from excessive camber: Wear

from positive camber is on the outside shoulder

of the tire; with negative camber, wear is on the

inside shoulder.

Caster is the forward or rearward tilt of the

steering axis in reference to a vertical line. The

angle is measured in degrees. Caster is positive

when the top of the steering axis is tilted rear ward

and is negative when the tilt is for ward. Caster is

usually a factor in vehicle handling, but can affect

tire wear. Proper caster is important for directional

stability and returnability. Improper caster can

cause shimmy, excessive steering effort, pulling

and shoulder wear on the steer tires.

Turning Angle

Turning angle is the difference in the angles of

the front wheels in a turn. This measurement is an

aid in diagnosing steering problems and irregular

tire wear. Improper turning angle may cause

scuffing, leading to excessive tire wear.

18°

20°

Positive Negative

–+

Positive Negative

–+

Caster: A Factor in

Vehicle Handling

– 3 –

Tandem Axle Angles

Geometric centerline of a vehicle is a line

drawn through the midpoints of the front axle and

the rear reference axle.

Tandem scrub angle is the angle formed by the

two thrust lines of a tandem axle vehicle.

In the diagram below, misalignment causes the

tandem axles to work against each other.

The steer axle must be turned to offset the “push” of

the axles and keep the vehicle moving straight ahead.

This causes every tire on the vehicle to scrub.

Tire wear from tandem scrub occurs at the

leading edge of the steer tires, in a pattern called

“inside/outside” wear. For example, on the front

axle of this vehicle, wear would occur on the

outside of the left steer tire and on the inside of

the right steer tire. Tire wear would occur on all

drive axle tires.

Thrust line is the bisector of the total toe angle

of an axle. It represents the direction the axle

“points” compared to the centerline of the vehicle.

Thrust angle is the angle formed by the

geometric centerline and the thrust line of an axle.

Geometric

Centerline

Geometric

Centerline

Geometric

Centerline

Thrust

Line

Thrust

Angle

Tandem

Scrub

Angle

– 4 –

Trailer Alignment

and Tire Wear

Alignment Angles Affect

Rolling Resistance and

Fuel Consumption

Misaligned trailer axles cause tandem scrub,

resulting in rapid wear on all tires.

If the trailer doesn’t track correctly, it exposes

more area to wind resistance. This can af fect

handling and fuel economy.

While the effects of misalignment show clearly in

tire wear, the effects on fuel consumption are less

easy to quantify. Fuel consumption is affected by

many factors.

However, it is obvious that misalignment must

increase rolling resistance – and rolling resistance

is a major cause of fuel consumption.

Scrub

Angle

The same conditions that cause tandem scrub on

tractors also apply to tractor-trailer combinations.

Geometric Centerline

Alignment

Geometric Centerline Alignment can be used as a

reference from which to compute individual toe

angles. The Geometric Centerline of a vehicle is

established by placing a line from the midpoint of

the front axle and the midpoint of the rear -most axle.

The Geometric Centerline is not based on frame

rails or cross member reference points.

The alignment system will establish the

Geometric Centerline.

Geometric

Centerline

– 5 –

Frame Centerline Alignment

Separation

Frame

Centerline

Sensor

Centerline

– 6 –

Frame offset angle is the angle of the frame referenced to the sensor

centerline. This angle is calculated by the aligner when frame offset

measurements are entered into the aligner.

Separation is the distance between the reference

axle adjustment points. This distance may be

measured and entered into the aligner before

adjusting thrust angle to allow the aligner to

calculate how much the axle must be moved at

the adjustment point.

WinAlign®HD software supports more than 60

customized truck, trailer and bus alignment procedures

as well as passenger car and light truck alignment.

Advantages of Computerized Alignment

A customized HD specification data base

supports most vehicle manufacturers by simply

scrolling to the specific model being aligned.

WinAlign ®HD Software

– 7 –

Pro-Comp®allows the technician to mount and

compensate one sensor at a time or four

technicians to mount and compensate at one time.

Pro-Comp tracks the amount of runout at each

wheel position once compensation is complete

and flags the technician when excessive runout

exists.

Pro-Comp continuously tracks runout at each

wheel so the need to keep the wheel adapters

straight up and down is no longer necessar y.

A self centering wheel adaptor centers itself and

remains centered as the technician clamps the

adapter to the rim (18" - 24" diameter capacity).

Compensation Control ScreenVehicle Specifications

The “Vehicle Specifications” primary screen

displays the identification and alignment

specifications for the vehicle chosen.

The technician may be asked to enter a reference

diameter. He can measure the front tire diameter

and enter that value in “Reference Diameter.”

When activated, ExpressAlign®tool bar (visible in

top, right hand corner of aligner screen)

automatically shows the customized alignment

path for the vehicle selected.

ExpressAlign allows movement in procedure by

using the mouse and selecting the respective icon

relative to sensor location.

– 8 –

WinAlignHD automatically calculates the

correction required. As the adjustment is made,

the arrow moves across the bar graph target

guiding the technician. When the adjustment

comes within specification the bar graph

changes from red to green.

WinAlignHD allows the user to print any screen

for records or to show the vehicle owner the

need for service. Before and after alignment

measurement screens can be printed to show

any out-of-spec. condition. Screens can be

printed anytime as a guide for the technician.

Automatic Calculation

Print Any Screen

WinAlign®HD provides precise measurements and

display. DSP500T Sensors with optional wireless

high frequency spread spectrum transmitters allow

quick set up. Measurements are compared with

the manufacturers specification and results are

shown on the vehicle measurement display screen.

Easy-to-read color coding identifies in- and out-

of-specification measurements.

WinAlignHD allows frame offset measurements

to be input and displays frame offset angle,

recalculating thrust angle from the geometric

centerline of the frame.

Precise Measurement Display

Frame Offset

– 9 –

Total Alignment

In the total alignment procedure, ever y axle on

the vehicle is measured and the axles are set

parallel – so all the wheels roll in the same

direction, minimizing rolling resistance.

1. Electronic sensors are mounted on the steer

axle and on one of the tandem drive axles

(the reference axle). The sensors are

compensated for runout.

2. The rear reference axle is measured to

determine the thrust angle. If adjustable, it is

aligned to point down the frame centerline.

3. The steer axle is aligned to the rear

reference axle.

4. Sensors are moved from the front axle to the

second rear axle. This axle is aligned to the

reference axle.

For other vehicle configurations, similar

procedures are followed, aligning all axles to a

reference axle. 37 pre-programmed procedures

are built into this system’s software.

– 10 –

A computerized alignment system should have

the capacity to recognize several factors that

can affect alignment.

Compensation for Runout

Runout, due to bent or distorted rims, is

common on heavy duty trucks and trailers. The

aligner electronically compensates each sensor

and correctly measures where the axle points.

Identifies and Corrects for Offset

Axle offset on heavy duty trucks and trailers is due,

for example, to mismatched rims. The aligner

allows the technician to measure the distances and

input those measurements, automatically

correcting for offset.

Frame

Centerline

Sensor

Centerline

Recognizing Factors That

Can “Fool” the Alignment

Technician

Wheel Balance and Its

Effect on Tire Wear

When aligning the wheels don’t forget

about the importance of proper balance.

Maximizing tire wear requires proper

balance in addition to alignment.

When a wheel and tire assembly is in balance,

gravity will not allow it to rotate from a stopped

position. If the assembly is out of balance,

gravity will force it to rotate when the heavy

portion is in any position but straight down.

When the wheel is put in motion, centrifugal

force acts on the heavy spot, causing the

rotating assembly to pull away from its axis.

The resulting force causes the wheel to “hop.”

This causes vibration and increased tread wear

in the form of “cupping.”

– 11 –

*offset exaggerated for example purposes

*

– 12 –

Even wear across the

center with worn strips

around the shoulder.

Excessive wear

extended across the

entire shoulder rib to

a major tread groove.

Circumferential

wear along the rib

edges next to major

tread grooves.

Tread ribs worn so that

one side is higher,

resulting in step-offs

across the tread.

Typical of a radial

ply rib type.

Rotation.

Measure and align

all wheels. If wear is

severe, rotate tires.

Characteristic of slow

wear rate of radial tires

on free rolling axles.

Scrubbing due to

incorrect alignment,

front and/or rear

defective suspension or

steering components.

Scrubbing due to a rear

axle misalignment.

This wear should not be

a concern unless the

wear becomes too deep.

Tires can be rotated to

drive axles at this point.

Replace worn parts,

align vehicle, and if

wear patterns are

severe, rotate tires.

Irregular Tire Wear Guide (Steer Tires)

Description Appearance Possible Cause Solution

Shoulder step wear

Full shoulder wear

Erosion/river

channel/wear

Feathered or

sawtoothed wear

Over-inflation wear

Excessive wear in the

center of the tread –

when properly inflated,

the tire appears to cup

when viewed across

the tread face.

Over-inflation

expands the tire

forcing more wear in

the center of the tread.

Keep tires properly

inflated.

– 13 –

Localized patches of

fast wear creating a

scalloped appearance.

Diagonal wear - flat

spots worn diagonally.

Localized flat spots

across the tread, often

repeating around the

tread circumference.

Even wear across

tread face and

around tire

circumference.

Tread depth varies

around tire with

maximum difference

approximately 180

degrees apart.

A result of moderate to

severe assembly out of

balance condition.

Diagnose imbalance

condition. Tires

should be rotated to

drive axle.

Mount as outside drive

dual with change in

rotation of tire.

Heavy axle loads;

such wear often

occurs on short

wheelbase tractors and

on long wheelbase

straight trucks.

Usually a result of

excessive radial runout

or non-uniformity in

the rotating assembly.

Runout and/or out of

balance in conjunction

with a slow rate of

wear. Can also be

caused by a loose

wheel bearing.

Carefully match

equipment with service

requirements. Consult

vehicle and tire

manufacturers when

specifying equipment

or replacing tires.

Replace or correct

as necessary. Rotate

tire to trailer dual.

Description Appearance Possible Cause Solution

Cupping/scallop wear/

dished out areas

Diagonal wear - flat

spots worn diagonally

Overall fast wear -

good wear pattern, but

fast rate of wear

Out of round tire

Under-inflation wear

Tread is worn unevenly

toward the edges of the

tire – when properly

inflated the tire appears

round when viewed

across the tread face.

Under-inflation causes

the tire to collapse,

forcing more wear on

the edges of the tread.

Keep tires properly

inflated.

– 14 –

Troubleshooting Guide

Symptom Possible Cause

Pull Left/Right Uneven tire pressure

Uneven tread wear

Mismatched tires

Uneven camber

Uneven caster

Brake drag

Suspension/frame sag

Unbalanced power assist

Bent spindle

Worn suspension components (front/rear)

Excessive tandem scrub

Centerline Steering Error Incorrect front toe

Rear wheel misalignment

Excessive steering and suspension play

Excessive gearbox play

Gearbox loose at the frame

Shimmy Excessive positive caster

Wheel imbalance

Defective suspension and steering components

Excessive wheel and tire runout (lateral)

Worn tires

Under inflation

Steering gear loose

Excessively loose wheel bearings

Ply separation or blister

Improperly torqued lug nuts

Vibration Wheel imbalance

Excessive wheel and tire runout (axial)

Drum imbalance

Drive shaft imbalance

Defective u-joints

Defective wheel bearings

Improper tire inflation

Drivetrain misalignment

Defective shock or shock mounting

Defective tire

– 15 –

Troubleshooting Guide (cont.)

Symptom Possible Cause

Noise (abnormal) Defective wheel bearing

Overinflation

Coarse tread pattern

Incorrect alignment (all wheels)

Incorrect turning angle

Loose or rubbing suspension or steering component

Driveline misalignment

Hard Steering Low air pressure

Steering gear binding

Steering lubricant low

Excessive positive caster

Defective power steering belt

Power steering fluid level low

Power steering pressure low

Steering and suspension component dry or binding

Loose Steering Excessively loose wheel bearings

Worn steering and suspension components

Steering gear assembly loose on mounting

Excessive internal wear in steering gear

Loose or worn steering shaft coupling

Steering gear misadjusted

Excessive Road Shock Excessive positive caster

Low air pressure

Worn tires

Wrong type tire

Wrong shocks

Worn shocks

Springs worn or sagged

Braking Instability Brakes incorrectly adjusted

Contaminated brake linings

Defective suspension components

Incorrect alignment

Excessive negative caster

Uneven or low tire pressure

– 16 –

Troubleshooting Guide (cont.)

Symptom Possible Cause

Poor Returnability Incorrect caster

Low air pressure

Binding suspension and steering components

Binding steering gear

Wander/Instability Incorrect alignment

Worn tires

Low air pressure

Mismatched tires

Worn suspension and steering components

Worn or loose steering gear

Misadjusted steering gear

Excessively loose wheel bearings

Squeal/Scuff on Turns Worn tires

Low tire pressure

Incorrect turning angle

Poor driving habits

Worn suspension or steering components

Excessive Body Sway Worn shocks or mountings

Broken or sagging springs

Uneven vehicle load

Uneven tire pressure

– 17 –

Power Steering Troubleshooting Guide

Symptom Possible Cause

Insufficient Assist Low fluid

Incorrect fluid

Loose/worn belt

Defective pump

Restricted fluid passages

Mechanical bind

Vehicle Pulls Inoperative control valve

Misadjusted control valve

Fluid Leaks Loose hose connection

Defective hose

Damaged seals

Fluid level too high

Excessive Noise Low fluid level

Loose/worn belt

Defective pump

Restricted fluid passages

Defective relief valve

Poor Returnability Steering column misalignment

Yoke plug too tight

Valve assembly binding

Contaminated fluid

Defective u-joints

– 18 –

Facility Factors

How Much Space

is Required?

Wheel alignment for heavy duty vehicles is not

space intensive.

The alignment console is usually mounted on a

mobile cabinet that can be rolled to the vehicle.

Overall dimensions of a console with a 19"

monitor and truck & bus sensors mounted are 65"

high by 33" deep by 72" wide.

Space for the console and the vehicle, and working

room for the technician is all that is required.

Is a Pit Rack Needed?

A pit rack has definite advantages in providing

room underneath a vehicle for inspection,

alignment and suspension repairs.

However the only equipment needed for toe,

scrub and thrust angle (the most important

adjustments to be made) are the alignment

system, turning angle gauges (standard

equipment with the Hunter system) and a jack

for lifting the vehicle during the procedure.

Technicians and Training

– 19 –

Finding an Alignment

Technician

Most experienced heavy duty technicians can

learn alignment quickly, especially with the help

of a computerized system and on-site training.

Alignment Training

Hunter Engineering Company routinely offers

heavy-duty truck alignment courses. These

courses provide extensive hands-on experience

with equipment and vehicles.

On-site training is offered at the time of

equipment installation, with retraining available

when new technicians are hired.

Training in Merchandising

of Alignment

Surprisingly, many experienced people in the

trucking industry have only a minimal

understanding of wheel alignment and its effects

on tire wear, fuel consumption and vehicle

handling. Because of this, the technician or

service manager may need help in merchandising

alignment service.

Hands-on training in alignment merchandising

should be as much a part of the equipment

”package” as operations training. See your local

Hunter representative for details.

Pamphlets and brochures can be used at the shop

location and in working with fleet management.

To properly align heavy-duty trucks, buses and trailers,

it is necessary to first determine the axle configuration.

On vehicles with more than two axles it is also

necessary to determine which axle should be used as a

reference axle. Some axles are not adjustable,

therefore that axle must be used as the refer ence axle.

Truck/Bus/Trailer Axle Configurations

Truck/Bus/Trailer

Alignment Procedures

The other axles are then aligned to the non-adjustable

reference axle of an all wheel alignment. If all axles are

adjustable, the rearmost drive axle is generally used as

the reference axle.

Use the following diagrams to determine which alignment

procedure should be used for the vehicle being aligned.

– 20 –

Busses

Trucks

Truck/Bus/Trailer Axle Configurations (cont.)

– 21 –

Dollies

Full Trailers

Semi-Trailers

Cars/Light Trucks

Glossary

Ackerman Principle: An alignment principle based on

vehicle tread width and wheelbase upon which turning

angle is computed.

Ackerman Arm: A steering component, which provides

interconnection between the outer tie rod and spindle.

Alignment: The process of measuring and adjusting the

position of all wheels attached to a common chassis.

Angle: Two intersecting lines that are not parallel.

Arc: Any part of a circle or a cur ved line.

Axial Play: Vertical movement of the wheel and tire

assembly when inspecting a kingpin.

Balance: This term is used to describe having equal

weight distribution about the circumference of a wheel

and tire assembly.

Bead: A wire steel coil forming an anchor for individual

plies and rim attachment of a tire.

Bellows: A rubber type seal, which is folded to allow

for a telescopic action. Normally referred to as a

bellows boot.

Bias Belted: A bias ply tire that has reinforcing strips

or belts under the tread section.

Bias Ply: A tire constructed of alternate plies, which

intersect the tire centerline at approximately 35 degrees.

Body Roll: The leaning of the vehicle body

while cornering.

Braking Control: Vehicle stability related to the

reaction under all stopping conditions.

Bushing: A component made of metal or rubber-type

material, used to isolate interconnected moving parts.

Cam Bolt: A bolt and eccentric assembly which, when

rotated, will force components to change position.

Camber: The inward or outward tilt of the wheel.

Camber Roll: A change in camber brought about by

suspension changes while cornering.

Caster: The forward or rearward tilt of the steering axis.

Center Bolt: A bolt that provides centering and

attachment of an axle and spring assembly.

Centerline Steering: A centered steering wheel while

the vehicle is traveling a straight ahead course.

Chassis: All major assemblies on a vehicle including

suspension, steering, drivetrain, and frame. Ever ything,

except the body.

Circumference: The total distance around a circle.

Concentric: Two or more components sharing a

common center.

Conicity: A tire irregularity, which causes the tire to take

the shape of a cone when inflated and loaded. This may

generate a lateral force.

Contact Area: The total amount of tread surface that

contacts the road.

Cornering: The ease at which a vehicle travels a

curved path.

Cross Tube Assembly: Two tie rods and a tube, which

transfers the turning effort to the opposite side of the vehicle.

Curb Weight: The overall weight of a vehicle, less

passengers, luggage, or load.

Degree: A unit of measurement to describe an angle.

Dial Indicator: An instrument used to measure and display

linear displacement. Measurement is displayed on a dial face

and the scale is commonly graduated in thousandths.

Directional Stability: The tendency for a vehicle to

maintain a directed path.

Drag Link: A tube or rod used for interconnection between

Pitman Arm and tie-rod assemblies.

Dynamic Balance: This normally refers to the balance

condition of a wheel and tire assembly in motion.

Foot Pound: A unit of measurement used to describe

torque force.

Frame Angle: The angle formed by a horizontal line and a

line drawn parallel to the frame.

Geometric Centerline: A line drawn between the

midpoint of the front axle and the midpoint of the rear axle.

Horizontal: Parallel or level with the plane of the horizon.

Hub: The assembly that houses the bearings about which

the wheel and tire assembly rotates.

Hydraulic Pump: A power driven device generating

constant volume and pressure.

Included Angle: The sum of the angles, camber and SAI.

– 22 –

Independent Suspension: A suspension system that

provides an isolated mounting for each wheel to the chassis.

Individual Toe: The angle formed by a horizontal line

drawn through the plane of one wheel versus a centerline.

Intersect: The crossing point of two lines.

Jounce Travel: A suspension moving up through its travel.

Kinetic Balance: The balance condition of a rotating

wheel related to force generated in a vertical plane.

King Pin: A pin used to attach a spindle to an axle.

Lateral Run-out: Side-to-side movement with a rotating

wheel or tire.

Lead: A slight tendency for a vehicle to move away from

its directed course.

Linkage: A series of rods or levers used to transmit

motion or force.

Load Range: A system used to describe the ser vice or

weight limitations of a tire.

Memory Steer: A condition where the wheels, rather than

returning to straight ahead, tend to remember and seek a

previous position.

Millimeter: A unit of linear measurement. One millimeter is

equivalent to 0.039 inches.

Minute: A unit of measurement used to describe an angle.

One minute is equivalent to 1/60 of one degree.

Offset: The lateral displacement of a wheel or axle in

respect to a centerline.

Oscillate: A back and forth motion at a specific frequency.

Out-of-Round: A wheel and tire irregularity in which one

or both are not concentric with its axis of rotation.

Overinflation: Inflation pressure beyond that which

is recommended.

Oversteer: A characteristic in which a vehicle has a

tendency to turn sharper than the driver intends.

Parallelogram Steering Linkage: A steering linkage

design where if all pivot points were connected by lines,

these lines would be parallel.

Perpendicular: Being at right angles.

Pitman Arm: A steering component that provides

interconnection between the steering gear sector shaft and

the steering linkage.

Ply Rating: A method of rating tire strength. Not

necessarily indicative of the actual number of plies used.

Power Steering: A steering system that incorporates

hydraulics to assist in the steering of the wheels.

Pre-load: A predetermined amount of load or force

applied during assembly to prevent unwanted play

during actual operation.

Pull: The tendency for a vehicle to steer away fr om its

directed course.

Radial Play: Any lateral movement of the wheel and tire

assembly when inspecting a ball-joint or kingpin.

Radial Ply Tire: A tire construction type with alternating

plies 90 degrees to the tire bead.

Radius: The distance from the center to the outer edge

of a circle.

Rear Axle Departure Offset: The amount in inches from

the midpoint of the steer axle (or kingpin on a trailer), where

the projected thrustline intersects.

Rebound: A suspension moving down through its travel.

Recirculating Ball Steering Gear: A steering gear

design that is made up of a worm shaft, ball nut, and two

recirculating ball circuits.

Returnability: The tendency of the front wheels to return

to a straight ahead position.

Road Crown: The slope of a road from its center.

Road Feel: Necessary feedback transmitted from the road

surface up to the steering wheel.

Road Isolation: The ability of a vehicle to better separate

road irregularities from the driver and passengers.

Road Shock: An excessive amount of force transmitted

from the road surface up to the steering wheel.

Scrub Radius: The radius formed at the road surface

between the wheel centerline and steering axis.

Semi-Integral Power Assist: A power assist system

using a hydraulic pump and a power cylinder in conjunction

with the steering gear.

– 23 –

Setback: The angle formed between a centerline and a

line perpendicular to the front axle.

Shim: Thin material of fiber or metallic makeup used to

take up clearance between two parts.

Shimmy: A violent shake or oscillation of the front

wheels transmitted up to the steering wheel.

Shock Absorber: A suspension component used to

dampen spring oscillation.

Solid Axle Suspension: A suspension system

consisting of one steel or aluminum I-beam extended the

width of the vehicle.

Short Long Arm (SLA): An independent suspension

design incorporating unequal length control arms.

Spindle: A component on which a wheel and tir e

assembly rotates.

Stability: The tendency of a vehicle to maintain a

directed course.

Stabilizer: A steel bar used to minimize body r oll.

Steering Axis Inclination: The angle formed by

an imaginary line drawn through the steering axis

versus vertical.

Steering Gear: A mechanical device used to convert the

rotary motion at the steering wheel to a lateral motion.

Steering Shaft: A tube or rod, which interconnects the

steering wheel to a lateral motion.

Strut: Any support used between two parts.

Suspension: An assembly used to support weight,

absorb and dampen shock, help maintain tire contact and

proper wheel to chassis relationship.

Suspension Height: The specified distance between

one or more points on a vehicle to the road surface.

Tandem Lateral Offset: When the geometric centerline

does not cross the midpoint of all axles.

Tandem Scrub Angle: The angle formed by the

intersection of horizontal lines drawn through each rear

axle when total toe and the offset is zero.

Thrust Angle: The angle formed by thrustline and

geometric centerline.

Thrustline: A bisector of rear total toe.

Tie Rod Assembly: The outer most assemblies on a

parallelogram steering linkage. These assemblies are

attached to the drag link and Ackerman Arms.

Tie Rod End: The ball and socket assembly of a tie rod.

Tie Rod Sleeve: A threaded tube that provides connection

and adjustment of a tie rod assembly.

Tire Force Variation: A tire irregularity, in which there

is a difference in radial stiffness about the circumfer ence

of the tire.

Toe: The comparison of a horizontal line drawn through

both wheels of the same axle.

Turning Angle: The difference in the turning angle of the

front wheels in a turn.

Torsion Bar: A spring steel bar used in place of a

coil spring.

Tracking: The interrelated paths taken by the front and

rear wheels.

Treadwidth: The dimension as measured between the

centerlines of the wheels on the same axle.

Treadwear Indicators: Ridges molded between the ribs

of the tread that visibly indicate a worn tire.

Under Inflation: Air pressure below that which

is specified.

Understeer: A characteristic in which a vehicle has a

tendency to turn less than the driver intends.

Vertical: Being exactly upright or plumb.

Vibration: To constantly oscillate at a specific frequency.

Waddle: The lateral movement of a vehicle, usually caused

by some type of tire or wheel imperfection.

Wander: The tendency of a vehicle to drift to either side of

its directed course.

Wheelbase: The dimension as measured between the

center of the front and rear axles.

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