Low rolling resistant tires, or LRRTs, were first developed for the over-the-road trucking industry in response to increased federal scrutiny over corporate average fuel economy for commercial vehicles. So why aren’t more school buses using them?
Seventy-eight percent of nearly 200 School Transportation News readers responded to a survey last month and indicated they are not currently using LRRTs in their bus fleets.
For starters, traditional LRRTs tend to offer a more shallow tread depth than traditional truck and bus tires. The technology has become relatively commonplace for new tires used at axle positions, and for retreads on the trailer or drive axle, for trucks operating at higher speeds. But student transporters told STN that the tires are not ideal for stop-and-go school bus applications.
Ron Halley, vice president of fleet and facilities for school bus contractor Student Transportation of America, said he successfully used LRRTs with low-profile sidewalls for the FedEx Ground trailing fleet when he was a senior manager for the company. But the past six years with STA have taught him that those same low-profile sidewalls are not conducive for normal school bus operations.
“In a high scrub suburban environment with major sidewall hazards, [LRRTs are] really not the ideal application for [school buses],” he said, adding that STA does not currently spec LRRTs.
Robert T. Pudlewski, a retired vice president of fleet maintenance, technology and purchasing for Laidlaw, said LRRTs are generally manufactured from a softer type of rubber that is more subject to twists, turns and curb scuffs. He opined that LRRTs have the potential to wear out faster when used with school buses than with trucks.
However, Gary Schroeder, director of the global truck and bus tire business for Cooper Tire, told STN that a tire’s rolling resistance is impacted by all aspects of design, which is evolving.
“The tire’s shape, tread pattern, tread compound, and casing construction all play a role in the tire’s rolling resistance,” he explained. “The tire’s tread compound can have a large impact on the tire’s rolling resistance, and in some cases LRR tread compounds can be softer tread compounds. However, it is not always true that LRR tires have soft tread compounds.”
He added that purchasing LRRTs no longer means substituting shallow tread depth for increased fuel efficiency. He cited the low cost of ownership, or LCO, what he called a cornerstone of the Cooper Works Series line of tires. LCO offers deep tread depth on its drive and all-position tires, that is based on low initial acquisition cost, excellent tread wear, low rolling resistance, and a durable casing that is designed for retreadability.
“By providing this value, we are changing the paradigm that low rolling resistance tires must have a shallow tread depth,” he said. “We are able to provide a fuel-efficient tire with excellent tread wear.”
Tracking actual, real-world fuel economy improvements from LRRTs, however, is not as easy. While the U.S. EPA said LRRTs can reduce costs and emissions for long-haul class 8 tractor-trailers by more than 3 percent, little data is readily available for school buses.
While measuring the rolling resistance of tires in a controlled indoor test, Cooper Tire’s Schroeder said the company is seeing fuel economy improvements on the vehicle.
“Depending on the vehicle configuration and application, the tire’s rolling resistance will have a larger or smaller impact on fuel economy improvements,” he explained. “For example, Class 8 tractors that are in long-haul applications will realize the biggest impact from the improvements made to the tire’s rolling resistance. This is because the vehicle is running on the highway at steady state for long periods of time. Vehicles in more local service like a school bus experience more starting, stopping, and turning, which lessens the impact the tires have on fuel economy, but they will provide some benefit to fuel efficiency.”
Greenville ISD, located about an hour and half northeast of Dallas, has used the Cooper Roadmaster 234 for the past three years. Recently retired Director of Transportation Laura Carter told STN that LRRTs roll on all 44 of the district’s buses with “excellent results.”
“Our expected mileage on the 11R22.5 [tire] is around 40 to 45 thousand [miles], with most performing even better than that,” she explained.
Regardless of tread depth, wear, replacements or fuel economy, fleet experts all agree that the best way to ensure the longest tire life possible is via proper inflation. However, the recent STN reader survey also reflected that only 12.5 percent of 192 respondents currently use tire pressure monitoring systems.
“Tire maintenance is 100 percent about tire pressure,” said Pudlewski. “Don’t just check at the [preventive maintenance inspection]. There are still bus drivers thumping tires with a broom handle. TPMS is absolutely the best way to ensure proper inflation and to avoid blowouts.”
Cooper Tire’s Schroeder called proper tire inflation one of the keys to tire performance.
“Proper tire inflation pressure leads to optimal wear, durability and fuel efficiency,” he said. “All tires should have their inflation pressure checked on a regular basis, at least monthly. On a daily basis, tires should be inspected for any tire damage, penetrations, or irregular wear patterns.
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