Tires wear unevenly due to improper inflation, misalignment, and other reasons. Their position on the vehicle as well as your driving style and the condition of your suspension all play a role in how fast or slow tires wear down.
Tires should be inspected by maintenance people on a regular basis– for instance, a weekly check of all the tires on a vehicle is a smart idea. Since tires tend to pick up dirt, chemicals and debris, washing them often can help prolong their life.
Keep in mind a tire’s wear is generally most affected by its position on the vehicle. Front/steer tires are going to wear on the shoulders while drive tires will wear at the center. And rear tires get scrubbed so they’ll tend to wear down more quickly than the fronts.
If there’s a 3/32-5/32 difference in wear, it’s a good time to rotate the tires. Commercial trucks with uneven tires can sometimes experience different rotating speeds of the front and rear drive axles, so by rotating tires your inter-axle differential is likely to last longer.
Tire rotation is important because the goal is to have a smooth, efficient ride where all your tires are in the right positions for their condition. Eventually some tires will need retreading or replacing– that’s the nature of tires.
Opinions on when to rotate tires vary, ranging from “at least once during the life of the tread” to “at every oil change.” Different trucking companies have different policies for tire rotation.