Want the longest life out of your tires? Make sure all wheels of your tractor-trailer are properly aligned. Help's available in The Maintenance Council s Recommended Practice RP 642, "Total Vehicle Alignment: Recommendations for Maximizing Tire and Alignment-Related Component Life" It tells how to track tire life so you can spot problems while they can be fixed and before tires develop irreversible wear.
The RP suggests techniques to inspect tires, and provides forms to record results and track tire life. Good records can help you in working with truck or tire dealers, service companies and OEM factory service folks. The forms help you organize facts and show that you follow industry-accepted procedures, which helps in disputes. Here are some highlights:
Pre-Delivery Inspection
Inspect all tire and wheel assemblies. Look for tire wear (from delivery) or damage. Using a calibrated torque wrench, check all wheel nuts. Check tire inflation pressure. Do a pre-alignment check (described in appendix 10 of TMC RP 642). Instead of double checking others' work, ask the dealer if you can watch his inspection, which the manufacturer pays for. Then bring along a copy of RP 642 to see if the dealer follows accepted industry procedures.
First maintenance
Within the first 15,000 to 30,000 miles, or 90 days, inspect wheel assemblies and check for tire wear. Check and record tire inflation, on the same sheet(s) you used to record pre-delivery observations. Check torque at all wheel-end fasteners. Record everything, even if nothing has changed. Do the pre-alignment check described in the RP. Get an all wheel/all axle alignment. Make sure all measurements, both before and after the alignment, are recorded. If tire wear is uneven or irregular, rotate tires so they are rolling opposite to their original direction (unless you use directional tires).
Periodic Maintenance
Check and record cold tire inflation pressure with a calibrated tire gauge — a good tire shop can help verify its accuracy. At every PM, inspect and measure all tire and wheel assemblies for irregular wear. Record all findings. If you find irregular wear, rotate tires. Next PM, check if rotation has helped. If not, have the alignment checked. Every 80,000 to 100,000 miles, or 12 to 18 months, have an all-wheel alignment. Check for and repair worn or damaged components. When replacing a component that affects alignment, re-align the vehicle.
The RP shows various patterns of irregular tire, including:
Feather wear: One side of each tread block or rib is higher than the other, like a series of steps across the tread face, smooth in one direction with sharp peaks in the other. It's due to excessive toe (-in or -out), drive axle misalignment, worn or damaged suspension parts or other misalignment.
Cupping: a localized, dished-out wear pattern that creates a scalloped appearance around the tire. A tread depth gauge helps detect it early. Causes are imbalance, wheel-end play, weak or worn shock absorbers, or improper tire mounting.
Diagonal wear: Flat lines worn across the tread, at about 60 degrees to the direction of travel. The pattern repeats. Causes are bad wheel bearings, toe-out, mis-mounting wheels to the axle, mismatched duals or unequal inflation of duals. A skid can start it.
Rapid shoulder wear (one shoulder only): Wear on the edge of one shoulder. Caused by excessive toe or camber, a bent axle or worn wheel bearings.
One-sided wear: Like shoulder wear that has progressed too far. Causes are improper alignment, worn kingpins, loose wheel bearings, excessive camber, excessive axle loads, non-parallel axles or improper bead seating.
For a copy of RP 642, or the entire TMC Recommended Practices Manual, call (703) 838-1763.
