Your tires come with a diagnostic manual built into them. By “reading” tread wear, you can identify a number of problems and give yourself a smoother, safer and less expensive ride.

When you read your tire treads looking for problems, you’re looking for “irregular wear.” The Bridgestone/Firestone videotape “Saving Through Reducing Irregular Wear” makes it clear just what irregular wear is. Typical of over-the-road operations where a tire tread can last a long time, irregular wear is always a situation in which one part of the tread wears faster than another. The rub, so to speak, is that what wears out first always determines the removal mileage. So, the goal of good tire maintenance is to make the entire tread surface wear out at exactly the same time.

Some kinds of irregular wear – the spotty stuff that occurs because of uneven seating of the rim on the wheel, imbalance, bad shocks, or panic stops that lock the wheels – is like cancer. Once it starts, it grows, because the wear itself makes the tire hop up and down. That makes the wear continue in the same uneven pattern.

Other types of irregular wear occur either because the weight of the truck is not properly distributed on the tread, or because the wheels aren’t all headed down the road in the same direction. The latter situation, known as misalignment, will cause one or more tires to roll at an angle, producing what are called side forces. The tires are literally scrubbing sideways as they roll down the road. A 2-inch misalignment over a 181-inch. wheelbase means the steer tires have to pull the vehicle 58 feet to one side each mile. This is equivalent to scrubbing 1,100 miles sideways in 100,000 miles!

Doug Jones, support manager, North America, at Michelin N.A., Inc., recommends you think of the vehicle as a whole when doing alignment and that you follow the Technology and Maintenance Council’s Recommended Practice 642 covering Total Vehicle Alignment. The Bridgestone/Firestone tape makes it clear why this is so important. We usually think of alignment as a front end or front axle problem because the front axle does the steering, and, for that reason, has the most wearing parts. In fact, drive axles that are misaligned with each other and with the front axle present the most common misalignment problem on trucks. The second most common problem is trailer axle misalignment.

To do the alignment right, a tractor needs to be put on a large alignment rack, the most sophisticated of which use lasers, so that all the axles can be properly put in line. If you regularly pull the same trailer, its axles should be set at the same time.