School Bus Suspension Systems Enhance Ride Quality

Kelly Roher, Associate Editor
Posted on October 1, 2008
AIRTEK®, one of two front suspension systems for school buses manufactured by Hendrickson, features the STEERTEK axle, which improves vehicle stability, handling and maneuverability.
AIRTEK®, one of two front suspension systems for school buses manufactured by Hendrickson, features the STEERTEK axle, which improves vehicle stability, handling and maneuverability.

Equipping school buses with an effective suspension system is an integral part of ensuring the safety and comfort of everyone on board.

Fortunately, suspension systems available today have been designed to improve vehicle handling and stability and to absorb road shock for optimal driver and student comfort, either by working on a stand-alone basis or in conjunction with the vehicle’s existing suspension. Front and rear suspension systems are also known as steer and drive axle systems, respectively.

The following outlines product specifications from three companies that manufacture suspension systems for school buses and two that offer auxiliary systems.

Over the last decade, Hendrickson has increased its focus on the school bus market. The company strives to manufacture suspension systems that meet the needs of the major school bus OEMs, says Jacob Madden, segment manager for bus products.

Its AIRTEK® and SOFTEK® integrated front suspension and steer axle systems feature the fabricated STEERTEK axle, which Madden says is unique compared to I-beam axles because of its lightweight, box-shaped design, which resists horizontal, vertical and twisting forces to improve vehicle stability and handling.

Moreover, the STEERTEK axle allows for up to 55 degrees of wheel cut, facilitating ease of vehicle maneuverability.

While SOFTEK utilizes leaf springs and AIRTEK utilizes leaf springs and air bags, Madden says the leaf springs in both form a torsion system with the axle, thereby enhancing vehicle stability.

AIRTEK’s air springs and SOFTEK’s two-leaf spring design and premium shocks provide a smooth, comfortable ride.

For rear suspension, Hendrickson offers the COMFORT AIR® system. COMFORT AIR includes an extended main support member that generates a low spring rate for optimal roll stiffness and improved vehicle handling.

Its QUIK-ALIGN® feature aids in system adjustment and alignment, which Madden says reduces maintenance time.

“It has a wide footprint hanger that helps to distribute the vehicle load and road inputs over a large area,” he adds, “so it reduces stress to the vehicle frame.”

Finally, shock absorbers tuned for optimum dampening and air springs that adjust to changing load conditions improve ride quality.

Each of these systems is compatible with Type C and Type D school buses. Madden says Hendrickson has launched all three systems for Blue Bird, while IC Bus units can be equipped with the AIRTEK system and Thomas Built Buses units can be equipped with the COMFORT AIR system.

MOR/ryde International

MOR/ryde International's Rubber Leaf System features rubber shear springs that isolate and absorb road shock, providing a smooth ride. MOR/ryde International’s suspension systems for school buses work in conjunction with a bus chassis’ steel leaf spring suspension.

The vehicle’s rear hanger is replaced with a MOR/ryde frame hanger, a spring carrier and rubber shear springs. The MOR/ryde hanger bolts into the existing spring hanger holes on the chassis frame rail, providing a secure attachment that serves the same function as the leaf spring hanger.

In place of the leaf spring shackle or slipper setup, MOR/ryde’s spring carrier is attached to the leaf spring and the rubber shear springs. The spring carrier serves as the connection between the chassis leaf spring and the rubber shear springs.

The company offers a wide range of rubber shear springs that are available in different spring ratings and physical sizes. This allows each MOR/ryde system to match the vehicle’s axle rating.

Joel Badskey, MOR/ryde sales professional, says the use of rubber improves the performance of the vehicle’s existing suspension system. “Rubber isolates and absorbs road shock, giving you a softer, smoother ride,” he explains.

The systems also increase the dynamic axle travel of the vehicle’s existing suspension and are especially effective on applications where load conditions may vary, as the company’s specialty within the school bus market is systems for special-needs buses. For instance, the Rubber Leaf (RL) System — a drive axle system — is ideal for special-needs units, and it can be adjusted to level the bus.

Badskey says that wheelchair lift-equipped buses can be off-center, and while the system adjustment does not load-level like an air ride system, it levels out the weight at the beginning of a ride.

The RL System can be aftermarket installed or ordered directly from some OEMs. Installation is bolt-on and requires no welding.

MOR/ryde also manufactures the Steer Rubber Leaf System, a steer axle unit. Badskey says this system provides a more comfortable ride for the driver and typically works best on large school buses.

{+PAGEBREAK+} Ridewell Suspensions

Ridewell Suspensions' RAD-227 Parallelogram Air Ride System has four air springs that generate a particularly smooth ride, making it well suited for special-needs and activity buses. Ridewell Suspensions manufactures air ride systems for use on specialty applications within the school bus market.

The RAD-227 Parallelogram Air Ride System, for instance, is a drive axle system that includes four air springs. “Most air ride suspension systems only have two air springs per axle, so our four-spring suspension provides a particularly smooth and gentle ride,” says Rick Rickman, vice president of sales.

While Ridewell’s air ride suspension systems for school buses are more expensive than steel leaf spring systems, Rickman notes that the smooth ride created by the RAD-227 system’s four air springs makes it well suited for special-needs and school activity buses, as well as school buses that travel on extremely uneven streets.

In addition to the four air springs, the RAD-227 drive axle system’s parallelogram design provides constant axle pitch and maximum ride stability. Manual axle alignment is achieved through patented eccentric bolts, and all pivots are rubber-bushed for low maintenance.

Finally, Rickman says the company guarantees the durability of its air ride systems. “Our suspensions are designed for a 15-year lifespan,” he says. “A lot of activity and special-needs buses aren’t used as frequently as regular-ed school buses, and districts keep them for a long time. We’ve designed systems that will match that lifespan.”


Shackle system controls vehicle suspension

While the components of Hendrickson’s, Ridewell Suspensions’ and MOR/ryde International’s suspension systems improve ride quality, URO Systems LLC’s Shackle System further enhances ride quality by controlling the movement of a vehicle’s suspension.

The Shackle System has a freely rotating spring pin design and a specially formulated urethane that is self-lubricating and abrasion-resistant, making the system maintenance-free.

“Each of the pins at the hanger and the spring eye rotate,” explains Dan Teed, company president. “In many suspension systems they don’t, so the rotation translates to better vehicle handling, extended tire life and a smoother ride.”

The URO Shackle also reduces wear on the suspension’s leaf springs and hanger.

URO Systems offers several shackle replacement kits for school buses. The TD1410 and the TD1430 Front Shackle Replacement Kits, for instance, can be used on Blue Bird’s All American FE and RE units.

For Thomas Built Buses Saf-T-Liner EF units, URO offers the TD8820 Front Shackle Replacement Kit.


Focusing on the driver’s seat

LORD Corp.'s Motion Master Ride Management System includes a damper that utilizes magneto-rheological fluid technology to provide near real-time seat deceleration in response to road shock. When reviewing suspension system options for one’s fleet, it is important to consider the driver’s comfort as much as the students’ comfort.

As such, LORD Corp. offers the Motion Master Ride Management System, a seat suspension system that comprises a magneto-rheological (MR) fluid damper, a controller with an integral position sensor and a ride mode switch that can be set to soft, medium or firm.

“When installed under a seat, the controller’s arm provides seat position and velocity information to the system’s electronics and the damper is adjusted based on road conditions,” LORD Corp. Marketing Manager Jim Toscano explains.

The damper anticipates driver topping and bottoming and decelerates the seat to avoid end-stop hits from road shock, he adds.

The system’s ability to provide a near-instantaneous response to harsh road conditions stems from the MR fluid in the damper. “All you’re doing is changing the strength of the magnetic field, so you get a device that can respond in milliseconds,” Toscano says.

LORD Corp. offers the Motion Master system through Bostrom Seating Inc. It is available on Bostrom’s T-Series™ 915 seat.


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