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.
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. + – Toe-in Toe-out Results of excessive toe is wear on the leading edge of the tire. Total Toe is the angle formed by two horizontal lines through the planes of two wheels. T oe-in is when the horizontal lines intersect in front of the vehicle; Toe-out is when the horizontal lines intersect behind the wheels.
Tire Wear Due to Improper Camber Settings + Caster: A Factor in Vehicle Handling – Positive Positive Negative 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. + Negative Caster is the forward or rearward tilt of the steering axis in reference to a vertical line.
Tandem Axle Angles 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. Geometric Centerline 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. Geometric centerline of a vehicle is a line drawn through the midpoints of the front axle and the rear reference axle.
Trailer Alignment and Tire Wear Alignment Angles Affect Rolling Resistance and Fuel Consumption The same conditions that cause tandem scrub on tractors also apply to tractor-trailer combinations. While the effects of misalignment show clearly in tire wear, the effects on fuel consumption ar e 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.
Frame Centerline Alignment Sensor Centerline Frame Centerline 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 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.
Advantages of Computerized Alignment WinAlign ® HD Software WinAlign®HD software supports more than 60 customized truck, trailer and bus alignment procedures as well as passenger car and light truck alignment. –7– A customized HD specification data base supports most vehicle manufacturers by simply scrolling to the specific model being aligned.
Vehicle Specifications Compensation Control Screen The “Vehicle Specifications” primary screen displays the identification and alignment specifications for the vehicle chosen. Pro-Comp® allows the technician to mount and compensate one sensor at a time or four technicians to mount and compensate at one time. The technician may be asked to enter a reference diameter. He can measure the front tire diameter and enter that value in “Refer ence Diameter.
Precise Measurement Display Automatic Calculation 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 outof-specification measurements. WinAlignHD automatically calculates the correction required.
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. 3. The steer axle is aligned to the rear reference axle. 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. 4. Sensors are moved from the front axle to the second rear axle.
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. A computerized alignment system should have the capacity to recognize several factors that can affect alignment. When a wheel and tire assembly is in balance, gravity will not allow it to rotate from a stopped position.
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Irregular Tire Wear Guide (Steer Tires) Description Appearance Possible Cause Solution Even wear across the center with worn strips around the shoulder. Typical of a radial ply rib type. Rotation. Excessive wear extended across the entire shoulder rib to a major tread groove. Scrubbing due to a rear axle misalignment. Measure and align all wheels. If wear is severe, rotate tires. Tread ribs worn so that one side is higher, resulting in step-offs across the tread.
Description Appearance Possible Cause Solution 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. Localized patches of fast wear creating a scalloped appearance. A result of moderate to severe assembly out of balance condition. Diagnose imbalance condition. Tires should be rotated to drive axle.
Troubleshooting Guide Symptom Pull Left/Right Centerline Steering Error Possible Cause 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 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 an
Troubleshooting Guide (cont.
Troubleshooting Guide (cont.
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 Excessive Noise Poor Returnability Loose hose connection Defective hose Damaged seals Fluid level too high Low fluid level Loose/worn belt Defective pump Restricted fluid passages Defective relief valve Steering column misalignment Yoke plug too
Facility Factors How Much Space 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. Wheel alignment for heavy duty vehicles is not space intensive.
Truck/Bus/Trailer Alignment Procedures 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. The other axles are then aligned to the non-adjustable reference axle of an all wheel alignment.
Truck/Bus/Trailer Axle Configurations (cont.
Glossary Ackerman Principle: An alignment principle based on vehicle tread width and wheelbase upon which turning angle is computed. Chassis: All major assemblies on a vehicle including suspension, steering, drivetrain, and frame. Ever ything, except the body. Ackerman Arm: A steering component, which provides interconnection between the outer tie rod and spindle. Circumference: The total distance around a circle.
Pitman Arm: A steering component that provides interconnection between the steering gear sector shaft and the steering linkage. 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. Ply Rating: A method of rating tire strength. Not necessarily indicative of the actual number of plies used. Intersect: The crossing point of two lines.
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.