What is Proper Wheel Alignment?A properly aligned vehicle is one in which all wheels are aimed in the same direction. Some ver y lowtolerance or acceptable error is designed into each vehicle by the manufacturer (see the vehiclemanufacturer specifications).

How Can Wheel Alignment Benefit Your Operation?The number one and number two operating expenses in over -the-road transportation are fuel andtires respectively. Both are typically perceived as hard to control. Routine wheel alignment is themost 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 serviceperformed by qualified technicians is dif ficult to manage. As a result alignment is mostly addressedafter the damage has been done. Simply making alignment par t of a vehicle or fleet pr eventivemaintenance program allows operators to easily get a handle on this per ceived uncontrollableexpense.

Hunter recommends a minimum of two to three alignments per year or ever y 50,000to 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. Techniciansperforming repairs on heavy duty suspensions are in ef fect alignment technicians. The only requiredequipment is the precision measuring system.

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Alignment Angles and EffectsTire Wear Due to Improper Toe SettingsToe 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 horizontallines through the planes of two wheels. Toe-in iswhen the horizontal lines intersect in front of thevehicle; Toe-out is when the horizontal linesintersect behind the wheels.

Individual Toe is the angle drawn by a linedrawn through a plane of one wheel r eferencedto the thrust line of the vehicle. Toe-in is whenthe horizontal lines intersect in fr ont of thewheel. Toe-out is when the lines intersectbehind the wheel.

Excessive toe-out wears the inside of the tire.

Results of excessive toe is wear on theleading edge of the tire.

+ –

+ –

Toe-in Toe-outToe-out

Toe-in Toe-out

Toe-in

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

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Tire Wear Due to ImproperCamber Settings

Camber is the angle formed by the inward oroutward tilt of the wheel referenced to a ver ticalline. This angle is measured in degrees.Camber is positive when the wheel is tiltedoutward at the top and is negative when thewheel is tilted inward at the top.

Tire wear from excessive camber: Wearfrom positive camber is on the outside shoulderof the tire; with negative camber, wear is on theinside shoulder.

Caster is the forward or rearward tilt of thesteering axis in reference to a vertical line. Theangle is measured in degrees. Caster is positivewhen the top of the steering axis is tilted rear wardand is negative when the tilt is for ward. Caster isusually a factor in vehicle handling, but can affecttire wear. Proper caster is impor tant for directionalstability and returnability. Improper caster cancause shimmy, excessive steering effort, pullingand shoulder wear on the steer tires.

Turning AngleTurning angle is the difference in the angles ofthe front wheels in a turn. This measurement is anaid in diagnosing steering problems and irregulartire wear. Improper turning angle may causescuffing, leading to excessive tire wear.

18°

20°

Positive Negative

–+

Positive Negative

–+

Caster: A Factor in Vehicle Handling

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Tandem Axle Angles

Geometric centerline of a vehicle is a linedrawn through the midpoints of the front axle andthe rear reference axle.

Tandem scrub angle is the angle formed by thetwo thrust lines of a tandem axle vehicle.

In the diagram below, misalignment causes thetandem axles to work against each other.

The steer axle must be turned to offset the “push” ofthe axles and keep the vehicle moving straight ahead.This causes every tire on the vehicle to scrub.

Tire wear from tandem scrub occurs at theleading edge of the steer tir es, in a pattern called“inside/outside” wear. For example, on the frontaxle of this vehicle, wear would occur on theoutside of the left steer tire and on the inside ofthe right steer tire. Tire wear would occur on alldrive axle tires.

Thrust line is the bisector of the total toe angleof an axle. It represents the direction the axle“points” compared to the centerline of the vehicle.

Thrust angle is the angle formed by thegeometric centerline and the thrust line of an axle.

GeometricCenterline

GeometricCenterline

GeometricCenterline

ThrustLine

ThrustAngle

TandemScrubAngle

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Trailer Alignment and Tire Wear

Alignment Angles AffectRolling 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 exposesmore area to wind resistance. This can af fecthandling and fuel economy.

While the effects of misalignment show clearly intire wear, the effects on fuel consumption ar e lesseasy to quantify. Fuel consumption is affected bymany factors.

However, it is obvious that misalignment mustincrease rolling resistance – and rolling resistanceis a major cause of fuel consumption.

ScrubAngle

The same conditions that cause tandem scrub ontractors also apply to tractor-trailer combinations.

Geometric CenterlineAlignment

Geometric Centerline Alignment can be used as areference from which to compute individual toeangles. The Geometric Centerline of a vehicle isestablished by placing a line from the midpoint ofthe 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.

GeometricCenterline

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Frame Centerline Alignment

Separation

FrameCenterline

SensorCenterline

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Frame offset angle is the angle of the frame referenced to the sensorcenterline. This angle is calculated by the aligner when frame offsetmeasurements are entered into the aligner.

Separation is the distance between the referenceaxle adjustment points. This distance may bemeasured and entered into the aligner beforeadjusting thrust angle to allow the aligner tocalculate how much the axle must be moved atthe adjustment point.

WinAlign®HD software supports more than 60customized truck, trailer and bus alignment proceduresas well as passenger car and light truck alignment.

Advantages of Computerized Alignment

A customized HD specification data basesupports most vehicle manufacturers by simplyscrolling to the specific model being aligned.

WinAlign ® HD Software

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Pro-Comp® allows the technician to mount andcompensate one sensor at a time or fourtechnicians to mount and compensate at one time.

Pro-Comp tracks the amount of runout at eachwheel position once compensation is completeand flags the technician when excessive runoutexists.

Pro-Comp continuously tracks runout at eachwheel so the need to keep the wheel adaptersstraight up and down is no longer necessar y.

A self centering wheel adaptor centers itself andremains centered as the technician clamps theadapter to the rim (18" - 24" diameter capacity).

Compensation Control ScreenVehicle Specifications

The “Vehicle Specifications” primary screendisplays the identification and alignmentspecifications for the vehicle chosen.

The technician may be asked to enter a referencediameter. He can measure the front tire diameterand enter that value in “Refer ence Diameter.”

When activated, ExpressAlign® tool bar (visible intop, right hand corner of aligner screen)automatically shows the customized alignmentpath for the vehicle selected.

ExpressAlign allows movement in procedure byusing the mouse and selecting the respective iconrelative to sensor location.

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WinAlignHD automatically calculates thecorrection required. As the adjustment is made,the arrow moves across the bar graph targetguiding the technician. When the adjustmentcomes within specification the bar graphchanges from red to green.

WinAlignHD allows the user to print any screenfor records or to show the vehicle owner theneed for service. Before and after alignmentmeasurement screens can be printed to showany out-of-spec. condition. Screens can beprinted anytime as a guide for the technician.

Automatic Calculation

Print Any Screen

WinAlign®HD provides precise measurements anddisplay. DSP500T Sensors with optional wirelesshigh frequency spread spectrum transmitters allowquick set up. Measurements are compared withthe manufacturers specification and results areshown on the vehicle measurement display screen.Easy-to-read color coding identifies in- and out-of-specification measurements.

WinAlignHD allows frame offset measurementsto be input and displays frame of fset angle,recalculating thrust angle from the geometriccenterline of the frame.

Precise Measurement Display

Frame Offset

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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 steeraxle and on one of the tandem drive axles(the reference axle). The sensors arecompensated for runout.

2. The rear reference axle is measured todetermine the thrust angle. If adjustable, it isaligned to point down the frame centerline.

3. The steer axle is aligned to the rearreference axle.

4. Sensors are moved from the front axle to thesecond rear axle. This axle is aligned to thereference axle.

For other vehicle configurations, similarprocedures are followed, aligning all axles to areference axle. 37 pre-programmed proceduresare built into this system’s software.

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A computerized alignment system should havethe capacity to recognize several factors thatcan affect alignment.

Compensation for RunoutRunout, due to bent or distor ted rims, iscommon on heavy duty trucks and trailers. Thealigner electronically compensates each sensorand correctly measures where the axle points.

Identifies and Corrects for OffsetAxle offset on heavy duty trucks and trailers is due,for example, to mismatched rims. The alignerallows the technician to measure the distances andinput those measurements, automaticallycorrecting for offset.

FrameCenterline

SensorCenterline

Recognizing Factors ThatCan “Fool” the AlignmentTechnician

Wheel Balance and ItsEffect on Tire WearWhen aligning the wheels don’t forgetabout the importance of proper balance.Maximizing tire wear requires properbalance in addition to alignment.

When a wheel and tire assembly is in balance,gravity will not allow it to rotate from a stoppedposition. If the assembly is out of balance,gravity will force it to rotate when the heavyportion is in any position but straight down.

When the wheel is put in motion, centrifugalforce acts on the heavy spot, causing therotating assembly to pull away fr om its axis.

The resulting force causes the wheel to “hop.”This causes vibration and increased tread wearin the form of “cupping.”

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*offset exaggerated for example purposes

*

– 12 –

Even wear across thecenter with worn stripsaround the shoulder.

Excessive wearextended across theentire shoulder rib toa major tread groove.

Circumferentialwear along the ribedges next to majortread grooves.

Tread ribs worn so thatone side is higher,resulting in step-offsacross the tread.

Typical of a radialply rib type.

Rotation.

Measure and alignall wheels. If wear issevere, rotate tires.

Characteristic of slowwear rate of radial tireson free rolling axles.

Scrubbing due toincorrect alignment,front and/or reardefective suspension orsteering components.

Scrubbing due to a rearaxle misalignment.

This wear should not bea concern unless thewear becomes too deep.Tires can be rotated todrive axles at this point.

Replace worn parts,align vehicle, and ifwear patterns aresevere, rotate tires.

Irregular Tire Wear Guide (Steer Tires)Description Appearance Possible Cause Solution

Shoulder step wear

Full shoulder wear

Erosion/riverchannel/wear

Feathered orsawtoothed wear

Over-inflation wear

Excessive wear in thecenter of the tread –when properly inflated,the tire appears to cupwhen viewed acrossthe tread face.

Over-inflationexpands the tireforcing more wear inthe center of the tread.

Keep tires properlyinflated.

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Localized patches offast wear creating ascalloped appearance.

Diagonal wear - flatspots worn diagonally.Localized flat spotsacross the tread, oftenrepeating around thetread circumference.

Even wear acrosstread face andaround tirecircumference.

Tread depth variesaround tire withmaximum differenceapproximately 180degrees apart.

A result of moderate tosevere assembly out ofbalance condition.

Diagnose imbalancecondition. Tiresshould be rotated todrive axle.

Mount as outside drivedual with change inrotation of tire.

Heavy axle loads; such wear often occurs on shortwheelbase tractors andon long wheelbasestraight trucks.

Usually a result ofexcessive radial runoutor non-uniformity inthe rotating assembly.

Runout and/or out ofbalance in conjunctionwith a slow rate ofwear. Can also becaused by a loosewheel bearing.

Carefully matchequipment with servicerequirements. Consultvehicle and tiremanufacturers whenspecifying equipmentor replacing tires.

Replace or correctas necessary. Rotatetire to trailer dual.

Description Appearance Possible Cause Solution

Cupping/scallop wear/dished out areas

Diagonal wear - flatspots worn diagonally

Overall fast wear -good wear pattern, but

fast rate of wear

Out of round tire

Under-inflation wear

Tread is worn unevenlytoward the edges of thetire – when properlyinflated the tire appearsround when viewedacross the tread face.

Under-inflation causesthe tire to collapse,forcing more wear onthe edges of the tread.

Keep tires properlyinflated.

– 14 –

Troubleshooting Guide Symptom Possible Cause

Pull Left/Right Uneven tire pressureUneven tread wearMismatched tiresUneven camberUneven casterBrake dragSuspension/frame sagUnbalanced power assistBent spindleWorn suspension components (front/rear)Excessive tandem scrub

Centerline Steering Error Incorrect front toeRear wheel misalignmentExcessive steering and suspension playExcessive gearbox playGearbox loose at the frame

Shimmy Excessive positive casterWheel imbalanceDefective suspension and steering componentsExcessive wheel and tire runout (lateral)Worn tiresUnder inflationSteering gear looseExcessively loose wheel bearingsPly separation or blisterImproperly torqued lug nuts

Vibration Wheel imbalanceExcessive wheel and tire runout (axial)Drum imbalanceDrive shaft imbalanceDefective u-jointsDefective wheel bearingsImproper tire inflationDrivetrain misalignmentDefective shock or shock mountingDefective tire

– 15 –

Troubleshooting Guide (cont.)Symptom Possible Cause

Noise (abnormal) Defective wheel bearingOverinflationCoarse tread patternIncorrect alignment (all wheels)Incorrect turning angleLoose or rubbing suspension or steering componentDriveline misalignment

Hard Steering Low air pressureSteering gear bindingSteering lubricant lowExcessive positive casterDefective power steering beltPower steering fluid level low Power steering pressure lowSteering and suspension component dry or binding

Loose Steering Excessively loose wheel bearingsWorn steering and suspension componentsSteering gear assembly loose on mountingExcessive internal wear in steering gearLoose or worn steering shaft couplingSteering gear misadjusted

Excessive Road Shock Excessive positive casterLow air pressureWorn tiresWrong type tireWrong shocksWorn shocksSprings worn or sagged

Braking Instability Brakes incorrectly adjustedContaminated brake liningsDefective suspension componentsIncorrect alignmentExcessive negative casterUneven or low tire pressure

– 16 –

Troubleshooting Guide (cont.)Symptom Possible Cause

Poor Returnability Incorrect casterLow air pressureBinding suspension and steering componentsBinding steering gear

Wander/Instability Incorrect alignmentWorn tiresLow air pressureMismatched tiresWorn suspension and steering componentsWorn or loose steering gearMisadjusted steering gearExcessively loose wheel bearings

Squeal/Scuff on Turns Worn tiresLow tire pressureIncorrect turning anglePoor driving habitsWorn suspension or steering components

Excessive Body Sway Worn shocks or mountingsBroken or sagging springsUneven vehicle loadUneven tire pressure

– 17 –

Power Steering Troubleshooting GuideSymptom Possible Cause

Insufficient Assist Low fluidIncorrect fluidLoose/worn beltDefective pumpRestricted fluid passagesMechanical bind

Vehicle Pulls Inoperative control valveMisadjusted control valve

Fluid Leaks Loose hose connectionDefective hoseDamaged sealsFluid level too high

Excessive Noise Low fluid levelLoose/worn beltDefective pumpRestricted fluid passagesDefective relief valve

Poor Returnability Steering column misalignmentYoke plug too tightValve assembly bindingContaminated fluidDefective u-joints

– 18 –

Facility FactorsHow Much Space is Required?Wheel alignment for heavy duty vehicles is notspace intensive.

The alignment console is usually mounted on amobile 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 workingroom for the technician is all that is required.

Is a Pit Rack Needed?A pit rack has definite advantages in providingroom underneath a vehicle for inspection,alignment and suspension repairs.

However the only equipment needed for toe,scrub and thrust angle (the most importantadjustments to be made) are the alignmentsystem, turning angle gauges (standardequipment with the Hunter system) and a jackfor lifting the vehicle during the procedure.

Technicians and Training

– 19 –

Finding an AlignmentTechnicianMost experienced heavy duty technicians canlearn alignment quickly, especially with the helpof a computerized system and on-site training.

Alignment TrainingHunter Engineering Company routinely offersheavy-duty truck alignment courses. Thesecourses provide extensive hands-on experiencewith equipment and vehicles.

On-site training is offered at the time ofequipment installation, with retraining availablewhen new technicians are hired.

Training in Merchandisingof AlignmentSurprisingly, many experienced people in thetrucking industry have only a minimalunderstanding of wheel alignment and its effectson tire wear, fuel consumption and vehiclehandling. Because of this, the technician orservice manager may need help in merchandisingalignment service.

Hands-on training in alignment merchandisingshould be as much a part of the equipment”package” as operations training. See your localHunter representative for details.

Pamphlets and brochures can be used at the shoplocation 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 alsonecessary to determine which axle should be used as areference 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-adjustablereference axle of an all wheel alignment. If all axles areadjustable, the rearmost drive axle is generally used asthe reference axle.

Use the following diagrams to determine which alignmentprocedure should be used for the vehicle being aligned.

– 20 –

BussesTrucks

Truck/Bus/Trailer Axle Configurations (cont.)

– 21 –

Dollies

Full Trailers

Semi-Trailers

Cars/Light Trucks

GlossaryAckerman Principle: An alignment principle based onvehicle tread width and wheelbase upon which turningangle is computed.

Ackerman Arm: A steering component, which providesinterconnection between the outer tie rod and spindle.

Alignment: The process of measuring and adjusting theposition 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 tir eassembly when inspecting a kingpin.

Balance: This term is used to describe having equalweight distribution about the circumference of a wheeland tire assembly.

Bead: A wire steel coil forming an anchor for individualplies 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, whichintersect the tire centerline at approximately 35 degrees.

Body Roll: The leaning of the vehicle body while cornering.

Braking Control: Vehicle stability related to thereaction under all stopping conditions.

Bushing: A component made of metal or rubber-typematerial, used to isolate interconnected moving parts.

Cam Bolt: A bolt and eccentric assembly which, whenrotated, will force components to change position.

Camber: The inward or outward tilt of the wheel.

Camber Roll: A change in camber brought about bysuspension changes while cornering.

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

Center Bolt: A bolt that provides centering andattachment of an axle and spring assembly.

Centerline Steering: A centered steering wheel whilethe vehicle is traveling a straight ahead course.

Chassis: All major assemblies on a vehicle includingsuspension, 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 maygenerate a lateral force.

Contact Area: The total amount of tread surface thatcontacts the road.

Cornering: The ease at which a vehicle travels a curved path.

Cross Tube Assembly: Two tie rods and a tube, whichtransfers the turning effort to the opposite side of the vehicle.

Curb Weight: The overall weight of a vehicle, lesspassengers, luggage, or load.

Degree: A unit of measurement to describe an angle.

Dial Indicator: An instrument used to measure and displaylinear displacement. Measurement is displayed on a dial faceand the scale is commonly graduated in thousandths.

Directional Stability: The tendency for a vehicle tomaintain a directed path.

Drag Link: A tube or rod used for interconnection betweenPitman Arm and tie-rod assemblies.

Dynamic Balance: This normally refers to the balancecondition of a wheel and tire assembly in motion.

Foot Pound: A unit of measurement used to describetorque force.

Frame Angle: The angle formed by a horizontal line and aline 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 generatingconstant volume and pressure.

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

– 22 –

Independent Suspension: A suspension system thatprovides an isolated mounting for each wheel to the chassis.

Individual Toe: The angle formed by a horizontal linedrawn 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 rotatingwheel 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 rotatingwheel 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 orweight limitations of a tire.

Memory Steer: A condition where the wheels, rather thanreturning to straight ahead, tend to remember and seek aprevious position.

Millimeter: A unit of linear measurement. One millimeter isequivalent 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 inrespect 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 atendency to turn sharper than the driver intends.

Parallelogram Steering Linkage: A steering linkagedesign 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 providesinterconnection between the steering gear sector shaft andthe steering linkage.

Ply Rating: A method of rating tire strength. Notnecessarily indicative of the actual number of plies used.

Power Steering: A steering system that incorporateshydraulics 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 itsdirected course.

Radial Play: Any lateral movement of the wheel and tireassembly when inspecting a ball-joint or kingpin.

Radial Ply Tire: A tire construction type with alternatingplies 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 fromthe midpoint of the steer axle (or kingpin on a trailer), wherethe projected thrustline intersects.

Rebound: A suspension moving down through its travel.

Recirculating Ball Steering Gear: A steering geardesign that is made up of a worm shaft, ball nut, and tworecirculating ball circuits.

Returnability: The tendency of the front wheels to returnto a straight ahead position.

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

Road Feel: Necessary feedback transmitted from the roadsurface up to the steering wheel.

Road Isolation: The ability of a vehicle to better separateroad irregularities from the driver and passengers.

Road Shock: An excessive amount of force transmittedfrom the road surface up to the steering wheel.

Scrub Radius: The radius formed at the road surfacebetween the wheel centerline and steering axis.

Semi-Integral Power Assist: A power assist systemusing a hydraulic pump and a power cylinder in conjunctionwith the steering gear.

– 23 –

Setback: The angle formed between a centerline and aline perpendicular to the front axle.

Shim: Thin material of fiber or metallic makeup used totake up clearance between two parts.

Shimmy: A violent shake or oscillation of the frontwheels transmitted up to the steering wheel.

Shock Absorber: A suspension component used todampen spring oscillation.

Solid Axle Suspension: A suspension systemconsisting of one steel or aluminum I-beam extended thewidth of the vehicle.

Short Long Arm (SLA): An independent suspensiondesign incorporating unequal length control arms.

Spindle: A component on which a wheel and tir eassembly rotates.

Stability: The tendency of a vehicle to maintain adirected 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 therotary motion at the steering wheel to a lateral motion.

Steering Shaft: A tube or rod, which interconnects thesteering wheel to a lateral motion.

Strut: Any support used between two par ts.

Suspension: An assembly used to support weight,absorb and dampen shock, help maintain tire contact andproper wheel to chassis relationship.

Suspension Height: The specified distance betweenone or more points on a vehicle to the road surface.

Tandem Lateral Offset: When the geometric centerlinedoes not cross the midpoint of all axles.

Tandem Scrub Angle: The angle formed by theintersection of horizontal lines drawn through each rearaxle when total toe and the offset is zero.

Thrust Angle: The angle formed by thrustline andgeometric centerline.

Thrustline: A bisector of rear total toe.

Tie Rod Assembly: The outer most assemblies on aparallelogram steering linkage. These assemblies areattached 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 connectionand 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 throughboth wheels of the same axle.

Turning Angle: The difference in the turning angle of thefront wheels in a turn.

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

Tracking: The interrelated paths taken by the fr ont and rear wheels.

Treadwidth: The dimension as measured between thecenterlines of the wheels on the same axle.

Treadwear Indicators: Ridges molded between the ribsof 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 atendency 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 causedby some type of tire or wheel imperfection.

Wander: The tendency of a vehicle to drift to either side ofits directed course.

Wheelbase: The dimension as measured between thecenter of the front and rear axles.

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