Tire industry officials view school buses as a pickup-and-delivery (or start-stop) application, as well as a high-scrub application due to the stops and turns they make while transporting students and the damage the tires can sustain from bumping or scraping against curbs.
As such, school buses must be equipped with tires that are built to accommodate frequent stops and that include compounds and features that protect against impacts, cuts and abrasions.
The following outlines the specifications of five manufacturers’ steer and drive tires that are well suited for these conditions.
Bridgestone Americas Inc.
Photo Above: Bridgestone America's R250 ED all-position radial steer tire has a cut- and chip-resistant compound to help protect it in harsh driving conditions.
Bridgestone Americas manufactures several steer tires for high-scrub, pickup-and-delivery applications. Guy Walenga, director of engineering for commercial products and technologies, says the company’s best model for school buses within this group is the R250 ED.
“This is a rib tire with a very scrub-resistant compound, so it can take a lot of the tight, full-lock turns that school buses make,” Walenga says. “It also has a cut- and chip-resistant compound because we see a lot of school buses go off onto unpaved routes and areas with gravel roads.”
Walenga says that the tire’s cut- and chip-resistant compound differentiates it from others on the market. “Everyone produces tires that have some sort of high-scrub compound, but not everyone applies cut and chip-resistance to those compounds,” he says.
In addition to five ribs with four wide grooves for improved handling and traction, the tire features sidewall protector ribs that reduce damage from cuts and impacts.
Another all-position radial tire offered by Bridgestone for steering applications is the R260F. This tire has stone rejectors in its main grooves to resist stone drilling, thereby protecting the tire’s belts and enhancing the durability of its casing.
Like the R250 ED, this model includes a high-scrub compound and sidewall protector ribs. The R260F’s Equalizer Rib design helps to combat irregular wear.
China Manufacturers Alliance LLC
CMA offers the Double Coin RR150, an all-position steer tire that features wide grooves to facilitate water evacuation and sipes to reduce tread tearing.
China Manufacturers Alliance (CMA) offers several Double Coin steer tires for school buses. The most commonly used models are the RR150 and the RT606+.
Vice President Aaron Murphy says these all-position tires have wide grooves to facilitate the evacuation of water and numerous sipes to keep the tread from tearing. The siping also helps to achieve good traction and establishes a good wear rate.
“We consider the school bus a high-scrub application,” Murphy says. “There are a lot of starts and stops, twists and turns, and scrubbing off of the tread. These tires have special compounds that [make them] ideal for [these conditions].”
The RR150 features improved contour for maximum strength, durability and retreadability, while the RT606+ has a deep tread (22/32) for longer original tread life. Both models have a solid shoulder to minimize tread cracking and enhance traction. They are available in sizes ranging from 10.00R20 to 295/75R22.5 and 11R22.5 to 295/75R22.5, respectively.
CMA also offers two steer tires that can be used for special-needs school buses. The RR400 has a wide shoulder, and its four steel belts enhance the unit’s toughness and stability and promote uniform wear. The RT500 low-profile tire also has four steel belts, as well as a five-rib tread design that allows for a long tread life. Their sizes span from 10R22.5 to 9.00R20 and from 225/70R19.5 to 255/70R22.5, respectively.
CMA offers two drive tires for fleet vehicles, including the RLB1 M&S (mud and snow), which features deep tread and full-depth siping for improved traction.
Goodyear Tire & Rubber Co.
TredLock technology in Goodyear Tire & Rubber Co.'s G661 HSA all-position steer tire stiffens and stabilizes the tread to prevent irregular wear.
Donn Kramer, director of marketing for commercial tires, says Goodyear Tire & Rubber Co.’s new all-position steer tire, the G661 HSA, is well suited for use on a school bus due to the vehicle’s relatively short runs and frequent turns.
Penetration protectors help resist cuts and punctures, and sidewall protector ribs coupled with a scrub-resistant sidewall compound protect against abrasions caused by curbing.
Moreover, the tire utilizes a multicompound construction to extend tread life. (This comprises one compound for the outer shoulder areas to facilitate even wear and another compound in the center to help achieve good mileage.) Kramer says this construction differentiates the tire from other all-position steer units in the industry.
Another differentiating component is its TredLock technology — interlocking microgrooves that stiffen and stabilize the tread.
“When the [vehicle] is [traveling] straight, the TredLock pattern is separated, which provides enhanced traction in wet weather conditions,” Kramer explains. “On a turn, those microgrooves come together to create a block, stabilizing the tread to help prevent irregular wear.”
The G661 HSA is available in 11R22.5; 295/75R22.5; and 11R24.5 sizes.
For drive tires, Goodyear offers the G622 RSD and the Unisteel G182 RSD. “Both are open on the shoulder area and have a blocky design for improved start-stop capability,” Kramer says.
Goodyear also offers a service called fleetHQ for its commercial fleet customers. “It’s a service network to provide information that helps customers improve their decision making relative to tire choice, service and other tire life cycle tools,” Kramer explains.
For more information, visit www.goodyear.com/truck/fleethq/fleets.html.
Hankook Tire America Corp.
Hankook Tire America Corp.'s Z35A radial drive unit has been SmartWay-certified by the EPA for its ability to reduce rolling resistance and improve fuel economy.
Brian Sheehey, director, commercial tire group, says Hankook Tire America offers two steer units that can be mounted on school buses. The AH11 is an all-position, pickup-and-delivery tire, while the AH12 is a medium-distance all-position tire.
The AH11 is built to withstand uneven wear, chips, cuts and tearing. Its tread design promotes lateral stability and precise handling in all weather conditions. The AH12 boasts a computer- designed tread pattern for even wear and extended tread life, as well as solid traction. It also optimizes fuel efficiency.
For drive tires, Hankook manufactures the DL01 and the Z35A. The first unit is a long-distance drive axle tire with extra-deep tread for good traction. The company says that end users will get many miles out of this tire, which features improved casing technology for greater durability.
Like the DL01, the Z35A radial tire offers excellent traction thanks to its large footprint and rugged tread design. This unit also includes a long-wearing compound that resists cuts, abrasions and stone retention.
Moreover, Sheehey says that the Z35A has received SmartWay certification by the EPA for its ability to reduce rolling resistance and improve fuel economy. (SmartWay signifies vehicles and products that reduce transportation- related emissions.)
Bill Bainbridge, director of brand communication, also notes the high quality of the Z35A, along with the quality of all Hankook tires for school buses.
“[Their quality] allows us to offer a comprehensive warranty that guarantees their original life from a workmanship and materials standpoint,” Bainbridge says. “It also guarantees that the tires can be used for multiple retreads.”
Michelin North America Inc.
Michelin North America's XZE2 all-position steer tire features Matrix siping technology and rib-edge microsipes to protect against irredgular wear.
Michelin North America’s newest all-position steer tire for regional, start-stop applications is the XZE2. This tire features Matrix siping technology (3-D Matrix sipes lock together) and ribedge microsipes to protect against irregular wear.
A full-width, elastic protector ply protects the working plies from bruising and penetration, while strong curb guards protect the tire’s sidewalls against impacts and abrasions.
“The XZE2 has a wider tread, which adds in stability,” says Chris Tolbert, business segment manager in marketing. “It also has stone ejectors within the tread.”
This tire is available in 11R22 and 275/80R22 sizes.
Another Michelin steer tire, the XZE, also features a wide, deep tread. It includes compounds for scrub resistance; the unit’s solid shoulders also help to resist scrubbing. Curb guards protect the sidewalls, and groove bottom protectors combat stone drilling.
The XZE comes in 9R22.5 and 12R22.5 for school bus applications.
The XDE M/S and the XDN2 are drive tires. The XDE M/S is an all-purpose tire for regional applications, and the XDN2 is an all-weather highway drive tire. The former features an open shoulder design for excellent traction while driving on loose soil or mud. The latter has wide, open shoulder grooves to provide extra traction. Moreover, like the XZE2, the XDN2 features Matrix sipes.
Michelin’s tires also help to optimize fuel economy. “We have the lowest rolling resistance of an all-wheel position within the regional segment,” Tolbert says. “Our compounds are designed to achieve a lower rolling resistance, [which] equates to lower fuel use.”
Retreading tires is important
Tire industry officials agree that retreading is an integral part of keeping fleets running smoothly and generating cost savings.
“Retreading is the original recycling,” says Guy Walenga of Bridgestone Americas Inc. “It helps keep operating costs low, and you’ll always have a safe and reliable tire.”
Adds Chris Tolbert of Michelin North America Inc.: “It benefits the fleet for uniformity purposes, and it’s an economical way to get the most out of [a tire’s] casing.”
The Tire Industry Association (formerly known as the International Tire & Rubber Association) has produced an informative booklet titled “Understanding Retreading” that explains the process.
To read about it, visit the Tire Retread & Repair Information Bureau at www.retread.org and click on “Understanding Retreading” on the left-hand side of the page.
This Website also has a wealth of information about the benefi ts of retreading.