With tires presenting a significant expense for school districts, it is important to have solid maintenance practices in place to get as much use out of them as possible.
Phil Mosier, the manager of commercial tire development for Cooper Tire, points to several factors that contribute to tire wear-and-tear.
“Every school district will be different as to how hard they are on their bus tires — the type of roads, obstacles encountered, weather conditions, and how the driver operates the bus, all come into play to determine a tire’s life,” he said.
School transportation is a tough application for tires, but with proper selection and maintenance practices, the tires on buses can reach their full potential in miles and in retreads, he adds.
Mosier shared with School Bus Fleet three tips to help ensure tire maintenance success:
1. Maintain Proper Inflation.
The number-one tip for longer tire life, hands-down, is maintaining proper inflation.
“That is key to a good tread footprint and even tread wear,” Mosier says.
The appropriate inflation figure should be determined by a scale weight by axle and then using a load/inflation table. For example, typically on a Blue Bird school bus, inflation levels for an 11R22.5 Load Range G are set at 105 psi. However, bus owners should plan to do their own inflation figure calculations for each bus model as the details vary, Mosier says.
It is also important to note, he adds, that mismatched inflation pressure on dual assemblies is a substantial contributor to faster tire wear.
“In an 11R22.5 tire size mounted in a dual assembly with the same new tread design, you would assume that they are the same size with the same circumference,” Mosier explains. “But, at just 5 psi difference in inflation, the lowest inflation tire will have a circumference that is 5/16 of an inch smaller.”
During every rotation cycle, the smaller circumference tire must scuff ahead to keep up with the tire with more inflation. These tires rotate around 500 times per mile, so simple math means 500 multiplied by 5/16 of an inch translates to 156.3-inches per mile, or 13 feet per mile, Mosier says.
“Imagine dragging a tire 13 feet every mile, with a full load of students in the bus,” he adds. “How many feet is that per day or per year? That illustrates clearly why you will see increased tire wear with improper pressure.”
2. Thorough Visual Inspections Are Crucial.
Mosier’s second tip addresses the need for performing thorough visual inspections.
Begin by looking at the sidewall facing out, he advises.
“It’s not uncommon to find some scuff or scrub marks, typically on the right-side tires due to right-hand turning where curbs are present, but what you’re really looking for is cracks, bulges or bubbles, and cuts,” he says.
Next, inspect the crown or tread area.
"Look for any road hazards such as nails, screws, or metal,” Mosier says.
He also recommends checking for cuts, chunking (missing sections of tread), or tearing that reveals the cords or belt package.
Lastly, inspect the inner sidewall when finished with the tread area, again checking for any cuts or bubbles.
“If you see anything that is compromising your tire, it should be removed from service,” he adds.
3. Rotate Tires Regularly.
Mosier’s third tip for optimal tire maintenance is to conduct regular tire rotations. Regular rotations can help get more miles out of every tire, putting off replacement.
“You really have to stay on top of rotations, especially in the positions where irregular tread wear can occur,” he says.
One of the things that happens when there is a change in the direction of the rotation, or when cross-rotating the tires, is “correcting” irregular wear areas, Mosier explains. Changing the direction of the rotation tends to even out heel/toe wear on the shoulders of drive tires. Steer tires are normally rotated side to side, which again changes the direction of rotation and helps even out wear.
Following these tips will not only optimize tire life, Mosier says, but will also position the tire casings to be in good shape for retreading, which can help contain maintenance costs.
“The way to extend your budget on tires is to get the most miles, coupled with the most retreads,” he adds. “Proper tire selection is one key to doing that, but it’s the maintenance practices that [you] follow that keep your buses operating as efficiently and safely as possible."