One of the most important parts of the pre-trip inspection of any school bus is the examination of the tires. Too many drivers merely thump the tires, a quick-but-inaccurate method of gauging satisfactory air pressure. Although most drivers understand how important oil is to the proper function of an engine, they don't always understand how critical proper inflation is to a tire. "These drivers don't understand the mechanics of the tire," says Greg Filer, director of national sales for Bandag Inc., a tire retreader headquartered in Muscatine, Iowa. "When a tire is underinflated, it generates heat, which decreases the life of the tire. If it gets hot enough, it will literally break down. In the worst-case scenario, the tire becomes a piece of rubber on the side of the road." Any tire that is 20 percent below the maintenance air pressure should be considered flat and must be removed and inspected to determine the cause of the lost pressure. Improper repairs are dangerous
While school bus operators need to be keenly aware of the pitfalls of improper tire inflation, they should also ensure that they practice proper tire repair. "This is one of the problems that we often see," says Filer. Improperly repaired tires are dangerous and can cause tire destruction and personal injury. For example, mechanics should never settle for a quick external repair of a nail hole with a sealant, rubber band or rivet-type plug. An improper repair such as this can allow moisture into the tire. This can lead to rust, which can destroy the steel belt of the casing. "The best thing is to use a certified repair technician," Filer says. When done properly, a repair should not limit the tire's retreadability. As a general rule, tires with the following damage should not be repaired:

• Damage caused by underinflation, such as wrinkling, corrugations and dislocations

• Sidewalls with noticeable creasing

• Ruptures, creases or detachment of radial ply too great in length Monitor tread depth
  Another important consideration for school bus operators is to track the tread depth of all the tires in the fleet. "Someone should be walking the yard, checking for pull points and any damage," Filer says. The tires should be pulled before the tread depth goes below 5/32 inch. If a tire is allowed to wear beyond that point, it may not be suitable for retreading. In addition, tires should be inspected for damage to the crown area, which could suffer from the following problems:

• Exposed belt cables

• Tire bulge

• Tread chunking

• Tread edge loosening The sidewall also should be carefully inspected for the following damage:

• Cracking

• Ply turn-up

• Bulging or rupture

• Blisters and bumps

• Abrasions