School Bus Tires and Basic Lesson Plans
June has arrived and the first year of the new century is passing quickly in the history books. At this point back in 1901, there were few dare we say none ®“ alternatives to walking, riding horseback, or hitching a wagon ride to the old schoolhouse. It’s also curious to imagine how the young students of 2101 will be transported, either actually or virtually, to their learning centers.
For now, that task is accomplished in large measure by a unique class of specially adapted and outfitted vehicles based on medium truck chassis components the yellow school bus.
Unlike fire engines and other emergency service vehicles, which can be ordered in several special high-awareness colors, all-purpose school bus is required by federal law to be painted “school bus yellow”, a special high-chrome color designed for universal recognition and reflectivity. These vehicles carry our most precious cargo, and a premium is placed on minimizing the possibility of mechanical failure or unscheduled downtime.
The majority of school bus operators perform their own maintenance. The average new bus is 40 feet long and carries from 66 to 71 passengers, depending on seat configuration, often dictated by state regulations. Since most school districts still have summer vacations for students from mid-June to mid-August, this off time is used for annual bus maintenance, typically including thorough mechanical inspections and tire servicing.
Popular Application Choices
Optimum tire selection for these buses is similar to many pickup/delivery operations. The first choice is based on road surfaces traveled, with pure over-the-road tires preferred on paved surfaces and mixed service (on/off road) tires used when routes include any significant portion of gravel or abrasive surfaces. Most pure highway tread tires are subject to tread chipping and stone damage on unpaved surfaces and the risk of casing damage and downtime exposure often outweighs the small additional cost of mixed service tires. Tires with buttressed or scuff resistant sidewalls are also popular.
The second basic choice is tread design. With the exception of a few locations in southern areas of the U.S., the preferred selection is a metro service-type rib tread tire on steer axles and a moderately aggressive traction tread on rear axles. As a general rule, pure line haul-type steer tires, especially those with decoupling grooves and special shoulder designs to retard irregular wear, should be avoided as these may be susceptible to rib tearing and chipping due to high side scuff/heavy wheel cut service typical of school bus applications.
Likewise, more aggressive traction tires designed for pickup/delivery service usually perform better on buses than deep tread, high mileage drive tires designed for tandem axle linehaul service, since the former tend to have improved wet and winter traction, especially under varying load conditions.
Tire sizing is an area where buses have fallen behind the trend to low profile designs. The majority of new buses are still spec’d with conventional 10R22.5 or 11R22.5 sizes. This may be because early low pro tires often had mileage shortfalls vs. conventional sizes due ,in part, to the shorter, stiffer sidewalls creating more abrasive scuff in the tread area at high wheel cut angles. Most major tire makers now offer newer types of metro service tires in low pro sizes designed to overcome this issue.
Also of note is a growing niche segment of specialized buses designed to address low platform/reduced step-up needs. Many of these utilize low profile 19.5-inch tires in place of traditional 22.5-inch sizes.
Bus Design Changes
Another consideration is the bus chassis layout. According to John Fay, director of school bus marketing for International Truck and Engine Corp., approximately 28% of new full-size buses are now flat-front, or transit style configurations with rear mounted pusher diesels and set back steer axles.
Improved maneuverability and larger passenger capacity are the primary advantages of these designs. Many of these require higher load range tires due to high steer axle loading. Extra-ply rated tires are fitted to drive axles as well for standardization and to facilitate retreading programs. Care must be taken to keep these tires separate in mixed fleets running both conventional- and transit-style buses.
Fay also notes that new buses are rapidly upgrading safety and convenience features. For example, ABS and power steering are now standard, and 97% of buses are equipped with automatic transmissions, up sharply in the past several years. Remote controlled heated mirrors, tilt steering wheels and other car-like features are being added to encourage drivers to concentrate on basic steering and braking functions.
Proper tire maintenance for school bus tires parallels the standard recommendations for metro service pickup/delivery trucks, with special emphasis on steer axle and inside dual tire inflation pressures and more frequent inspections for cuts, snags, bulges, or other damage. Also, many bus operators pull tires at slightly higher take-off mileage than in trucking applications. Tire wear due to alignment conditions can be severe because of the long wheelbase typical of most buses.
Ackermann steering geometry problems were typical of many buses for years, but manufacturers have corrected this in using modern computer programs to tailor steering arm configurations to wheelbase and design steering angles.
Fingertip diagnossis of steer tires is especially useful on buses to distinguish if shoulder wear is due to improper toe settings or a drive axle chassis thrust problem.
All told tire maintenance for school buses is pretty basic, but requires diligent execution to be effective. That’s the lesson plan.