Issue link: http://read.dmtmag.com/i/34501
SUSPENSIONS Forming the link between the truck and the tire, the suspension system provides a very important contribution to tire performance. The suspension must support the load and maintain the tire in the proper operating position on the road. If the suspension is in good operating order, the tires will track straight and be evenly loaded. This promotes slow, even wear and low tire cost-per-mile. Different truck manufacturers use different suspension systems. Some of these are adjustable for making minor changes, and some are not adjustable. All suspensions have parts that move and are, therefore, subject to wear. Worn or broken suspension parts are one of the main causes of irregular tire wear and handling concerns. (Ref. –Quick checks for system and suspension faults on Pages 60-62.) When observing irregular wear on a tire, first check for worn or broken front and rear suspension parts. AIR SUSPENSION SYSTEMS As vehicle manufacturers move away from multiple springs, there is an increased need to dampen the effect of road shock. Air suspension systems consist of fasteners and bushings with various components such as air springs, air or gas shocks, torque arms, air lines and valves held together by nuts and bolts. Day to day operations generate a constant twisting movement to all these parts and greater awareness and maintenance diligence should be paid to wear and proper torque to ensure proper performance of the system and the effect this has on tire life. All torque values should be verified to manufacturer’s specification, and new shock absorbers should be considered when installing new tires so as to maximize tire life. Shock absorbers used on air ride suspensions should typically provide effective dampening control for 150,000 miles of on-highway operations (100,000 for vocational applications). Refer to TMC RP 643, Air-Ride Suspension Maintenance Guidelines on air suspension systems. Routine inspection of trailer air suspensions should be scheduled to inspect connectors and bushings per manufacturer instructions. Pivot Bushing inspection should consist of taking measurements before disassembly to complete your inspection, complying with warranty* procedures, and replace the bushing if cracks or complete separation of the rubber is present. QUICK CHECKS FOR TRAILER SYSTEM FAULTS QUICK CHECKS WOULD INCLUDE: • Verify OEM alignment after 1,000-3,000 in-service miles • Verify rails are straight • Loose or missing fasteners, look for elongated holes • Damaged or bent brackets • Look for wear at u-bolts and springs – signs of movement • Look for signs of rust at track rod to indicate movement • Inspect torque arm clamp nuts and bolts for proper torque (check threads to see if stripped) • Verify spring beams are centered on hanger; if not, check alignment • Slider assembly movement, loose attaching bolts, u-bolt torque • Air-ride suspension movement • Insufficient lubrication • Worn shocks or springs • Bushings cracked or separated (inspect per manufacturer procedures) • Alignment (induced toe value at each dual position, negative camber, parallelism) • Worn or loose wheel bearings • Brake imbalance • Slow release of trailer brake systems • Operational conditions, high scrub application • Tire scrub/dragging at dock deliveries (commonly called Dock Walk) • Air pressure maintenance (improper for operation) • Overloaded/underinflated, high speed empty hauls • Mismatched pressure by dual position or axle • Mismatched tread depth/tire design by dual position • Improper tread depth for application/operation • New steer tire(s) mixed in trailer positions • Tire rotated from steer or drive with existing wear • Improper tire assembly mounting • Driving habits, improper use of trailer brakes * See warranty for details. 60 Section Three: Extending Tire Life