Features
Pre-emptive strike
You can prevent major tire catastrophes with a rigid schedule of tire inspections

By Paul Abelson
senior technical editor

 

Conventional wisdom heard at truck stops and repeated by shade-tree mechanics states that once you notice irregular wear on a tire, it's too late. Just fix what causes the wear so it doesn't get worse and run the tire as long as you can.

That wisdom is true … sometimes. But irregular tread wear can often be halted and in many cases corrected.

With new tires approaching $500, and retreads around $200, tires account for the greatest operating costs in trucking after fuel. That's why tire maintenance is important to profitable operations. But as with air pressure, the cause of many tire problems, tire conditions are checked too infrequently. Problems grow worse when left uncorrected, and they can't be corrected if they're not discovered.

That leads us to Rule No. 2 of tire maintenance. Rule No. 1, of course, is: Gauge your tire pressures at least weekly. Rule No. 2 is: Check tire conditions – treads and sidewalls – at least weekly.

It's hard to see problems on black tires, especially in the shade. Using a flashlight will help, but the best tools to check tire condition are your fingertips. Run them around the sidewall and shoulders, feeling for abnormalities: bumps, tears, chips, anything that might indicate serious damage or wear. Check for height differences on the tread surface between ribs or lugs. On rib tires, feel for changes in tread across the tire.

To help determine what maintenance needs to be done, the Technology and Maintenance Council developed a series of Recommended Practices that define and organize tire problems and present potential solutions or recommendations.

RP216B, the Radial Tire Condition's Analysis Guide, is a reference for examining damaged tires. The current version has 10 identified conditions in the bead area, including damage from overloading and flange wear; curling; and petroleum lubricants and fluid damage.

In the sidewall area, 26 conditions include sidewall separations induced by damage; tread puncture and bead damage; cuts and snags; abrasion; weathering and ozone cracking; sidewall blisters; damage from running flat; and circumferential (zipper) ruptures.

Crown and tread have 40 separate conditions. Brake lock skids and penetrations from road hazards are easily identified. But chain damage, tread separation, belt lift or separation, misaligned tread (sometimes found with retreads and rarely with new tires), impact breaks, and damage from road debris are not as easy to spot.

Interior conditions can only be found when the tire is demounted. Among 13 listed conditions are objects that have penetrated or split the inner liner, blisters and separations, impact breaks, inner liner bubbles, and pulled or loose cords.

When a tire has been run flat, it and the other dual should be demounted and inspected – the flat tire for damage because of riding on a rim, and the companion tire for problems because of overloading when taking the load of two tires. Such tires have exceeded load limits, often by 50 to 100 percent.

Often, problems arise from improper or failed repairs. The guide identifies 15 conditions, including repairs made without demounting the tire, spot repairs that should have been section repairs, unfilled nail holes and punctures, and improper patch placement.

Radial Tire Wear Conditions and Causes: A Guide to Wear Pattern Analysis, RP219B, is an aid for examining tread wear, broken into sections on steer, drive and trailer tires. Like its companion recommended practice, it describes the appearance of the wear pattern and lists probable causes and recommended actions for the tire, the vehicle and changes in operations.

Photographs illustrate each condition, showing the problem close up and its relationship to the tire as a whole. Line drawings clarify the pictures.

Space doesn't permit describing all 104 tire conditions and 28 wear patterns covered in the manual, but here are a few examples:

Steer tires
Out-of-round wear: A tire shows considerable difference in tread depth from the deepest tread to a point 180 degrees opposite where the shallowest tread is found.

Commonly caused by improper mounting or bead sealing, it can also be caused by damaged or defective components in the rotating assembly, including the hub, stud circle or wheel and rim. Distorted brake drums can also cause the problem.

Rotate the tires unless wear is severe. If so, consider having the tire retreaded. Check wheel end components if improper mounting wasn't the cause.

All truck tires have a molded circle called the GG ring. It's on the sidewall near the bead area to help check that mounting was done correctly. Whenever tires are mounted, double check that the GG ring is concentric with the rim. If not, have your service provider remount the tires.

Rib punch wear: It looks like someone randomly punched in portions of the ribs around the tire. It starts on the outer ribs and progresses to inner ribs.

The cause is often worn shock absorbers. But other mechanical problems can contribute. Improperly adjusted bearings or out-of-balance tires create rib punch wear, aggravated by high speeds and light loads.

Rotating will correct it if wear isn't too great. If it is, but the casing isn't damaged, consider retreading. Before putting the truck back in service, correct the mechanical problem.

Drive Tires
Block pumping, or alternate lug wear: This is when alternate lugs are worn to different depths. It's usually every second or third lug, but that could vary. It can be the result of mismatched air pressures in a set of duals and can be aggravated by worn suspension components.

The tire can be run safely to the end of its tread life, but you should check for any worn suspension components. Make sure inflation pressures are matched. Consider using a pressure equalizing device. Consult with your dealer to make sure you specify the best tire for your operations.

Heel/toe wear: Lugs are worn high to low from the front edge to the back in the direction of tire rotation. It can stem from mismatched inflation in a set of duals or the result of dual tires of significantly different diameters. Frequent starts and stops and high torque aggravate the conditions.

The tires can be run out. If the condition is severe, change the direction of rotation by rotating tires or remounting them.

Diagonal wear: Flat spots are worn at an angle of about 25 degrees to 35 degrees across the tread. The pattern repeats around the tread circumference.

Most causes involve equipment. Hub bearings can be out of adjustment. There may be toe-out (or toe-in) from tandem misalignment. Differences in tire diameter or inflation pressures may also affect wear, which can be aggravated by light loads and high speeds.

Tires can continue in service as long as tread is not worn below minimums, but the direction of rotation should be reversed. Check for mechanical causes and repair as needed.

Of course, not all conditions allow tires to be returned to service. Any time tire cord is exposed, for example, tires should be taken out of service.LL

 

truckwriter@anet.com


TMC Recommended Practices are written by members from suppliers and fleet maintenance managers, incorporating the collective wisdom of the industry. The manual will help answer all your maintenance questions. It's free with an owner-operator membership in TMC. Call 703-838-1763 to join.

March/April
Digital Edition