When do you change out a lift truck tire? Well, a couple of things to look for: Chunking, or gouging, separation of rubber from the wheel – Things that may be a little bit more obvious. One of the things that might not be obvious is tire volume. Tire volume has to do with these numbers placed on the tire sidewall. 21 by 7 by 15. The first number, 21 is the height of the tire. 7 is the width, 15 is the rim size. So we’re going to look at this. If this was measured out 2 inches less than the diameter from the floor to the top, it would be time to replace that tire. So if the height was 19, it would be that way. When you lose 2 inches on a standard size tire, you’re driving a truck 15-18% harder and farther than it needs to. simply because you now have a smaller tire, so you’re wearing out more pieces and parts than just the tire. One good reason to be checking out your tire wear, and volume on your tire.