BY ALAN M. PETRILLO
A fire vehicle starts with the suspension, whether it be leaf springs, rubber blocks, air ride suspensions, or independent types. These various styles of suspensions have many attributes that affect the type of rides they give firefighters on the rigs.
Dave Archer, vice president of engineering for Pierce Manufacturing Inc., says that Pierce installs suspensions from various manufacturers on its custom apparatus as well as its own proprietary suspensions, the TAK-4® Independent Front Suspension (IFS) and the TAK-4 T3 Independent Rear Suspension (IRS). Regarding the various types of suspensions, Archer points out that multileaf or stacked leaf suspensions can be used in any axle position and configuration and typically incorporate spring steel sections, or leafs, that are the same thickness and width and get shorter in length from the top down until the weight capacity is reached. The stacks can have eight or more leafs, all of which are bolted together with a common center bolt or pin and clamps on the longer sections that make direct contact with each other.
1 Pierce Manufacturing Inc. installed a TAK-4® Independent Front Suspension (IFS) on this engine it built for the Barona (CA) Fire Protection District. (Photos 1-2 courtesy of Pierce Manufacturing Inc.)
2 The Henrico County (VA) Division of Fire had Pierce install a TAK-4 T3 Independent Rear Suspension (IRS) on its new apparatus.
Parabolic leaf spring suspensions are similar to multileaf systems with regard to simplicity and maintenance with higher ride quality and lower stability, Archer says, while walking beam or bogie suspensions are only used in tandem drive axle configurations and in the heaviest applications. Such systems are typically very stiff but stable, he adds. Archer says that with an air ride suspension, height and ground clearance remain constant regardless of load weight but may reduce road feel and stability. “An air ride suspension provides for a comfortable ride with minimal maintenance and axle versatility,” he says. With an independent suspension, each wheel on the same axle can move vertically and react independently of the others. Independent suspensions typically offer the highest quality ride, handling characteristics, and the ability for each individual wheel to respond to what it encounters on the road separately from the other wheels on the vehicle, Archer maintains. “Pierce’s TAK-4 IFS on custom-built Pierce chassis provides a better road feel, control, and a smoother ride over any kind of surface,” Archer says. “Pierce also offers the TAK-4 T3™ IRS, which applies the same military-proven performance to rear ride performance.” Attributes of the TAK-4 systems, Archer says, include ride quality and control; greater maneuverability; high cramp angles; less wheel bounce, which improves steering and braking; and greater load carrying capacity.
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John Hinz, vice president of engineering for Reyco Granning, calls suspensions “the building blocks and one of the most important components of a fire apparatus.” He observes, “When specing, you need to consider if the apparatus is running in an urban, suburban, or rural area. You must consider turning radius, cramp angle, length of the vehicle, it’s wheelbase, and how well it can turn or maneuver at a scene to get into a critical position.”
3 Reyco Granning makes the IFS20FT independent front suspension that is available with up to a 55-degree cramp angle on a 20,000-pound axle. (Photos 3-4 co>urtesy of Reyco Granning.)
4 The 79KB mechanical spring suspension often used on a rear drive axle.
On steering suspensions, Hinz believes that the cramp angle should be a major consideration. “Cramp angle is the degree to which the steer tires can turn,” he points out. “The more the tires can turn, the greater the degree of turn angle, which means the tighter the turning circle. Our IFS20FT independent front suspension is available at up to 55 degrees cramp angle on a 20,000-pound axle, and our IFS24 has up to 48 degrees cramp angle on a 24,000-pound axle.”
Hinz adds that Reyco Granning offers hundreds of variants on its independent front suspensions. “There are 11 different cross members each for the 20,000-pound and 24,000-pound suspensions, designed to go around different turbo arrangements and cab rails,” he says. “Then you can adjust for the cramp angles. With the IFS20, you can get cramp angles of 42, 48, 53, and 55 degrees, and with the IFS24, you can get 42- and 48-degree cramp angles.”
Scott Ames, Reyco Granning’s director of sales, says that two of the company’s most used drive axle suspensions are its 79KB mechanical spring suspension and the 102AR air ride suspension. “Both are available with [gross vehicle weight ratings (GVWR)] of up to 35,000 pounds,” he says. “There’s an eccentric alignment feature available on those suspensions, and on the mechanical spring we have a fail-safe feature of a tongue that prevents rearward movement should a torque arm break.”
5 This is an example of a flat leaf front suspension on a Rosenbauer pumper. (Photos 5-6 courtesy of Rosenbauer.)
6 A Rosenbauer pumper is fitted with a Hendrickson Steertek NXT parabolic front suspension.
For ambulances, Reyco Granning makes the TransportMaster® line that combines its R-Series drive axle air suspension with an AirMaster® air supply module. “It’s a smart air control system that allows the system to use 80 percent less on-time of the air compressor leveling system, which works with the CPU to anticipate driver action,” Ames says. “The system sees what the operator is doing, whether braking, starting off, or rolling, and makes a decision based on what it sees.”
FRONT AND REAR AXLE CHOICES
Dave Scharphorn, chief executive officer of Rosenbauer Motors, says Rosenbauer uses Reyco Granning independent front suspension and Hendrickson Steertek™ NXT parabolic spring suspension for the front axles on its fire apparatus. “The Reyco Granning and Hendrickson systems give a smooth, cleaner ride than that of a multileaf spring system,” Scharphorn says. “They are the next step up for ride quality.”
On tandem rear axle apparatus, especially aerial platforms, Scharphorn says Rosenbauer most commonly uses air ride rubber spring suspensions. “With a heavy GVWR of 60,000 pounds, you want a suspension with very few moving parts to handle the load,” he notes. “On our 100-foot Viper SA (single axle) quint or 78-foot quint where we’re carrying a lot of water and extra hose load, we use the Hendrickson RoadMaax 35k Air Ride Suspension on our Commander chassis.”
7 Ferrara Fire Apparatus installed this Raydan Air Link™ air ride suspension, shown just out of paint, on the rear axle of one of its aerials. (Photos 7-8 courtesy of Ferrara Fire Apparatus.)
8 Ferrara uses Hendrickson Steertek NXT front steer axle systems on the front axles of its pumpers.
Drew Sutphen, president of Sutphen Corp., notes that Sutphen builds its own chassis and had been using multispring suspension on front axles; Hendrickson’s FireMaax EX heavy duty air suspensions for rear single axles; and Raydan Air Link™ suspensions, a combination of air ride and walking beam, for tandem rear axles. “Once we started seeing ride improvement with the FireMaax EX on the rear, we switched to Hendrickson’s Steertek NXT for about 70 percent of our front suspensions. Within six months, it will be our standard front suspension.”
Sutphen says that Steertek NXT suspensions give improved ride and handling characteristics and have a progressive rate bump stop for handling high dynamic loads, a custom tuned passive hydraulic dampener for smoother operation, and tighter turning radius of 45 degrees cramp angle for greater maneuverability. “And, the Steertek NXT suspension is up to 170 pounds lighter weight when compared to multileaf systems,” he adds.
Dan VanAlten, director of engineering for Ferrara Fire Apparatus, says that on pumper and Inferno chassis, Ferrara had been using modified spring suspensions from Navistar, flat leaf springs designed with thicker, higher grade steel so they wouldn’t sag over time. “Then we moved to parabolic springs custom made with Navistar hangers on the front, and recently we started using Hendrickson Steertek NXT front steer axle systems on the front axles.”
9 Liquid Spring makes the LiquidSpring® smart suspension for ambulances built on Ford, Chevy, International, DV, RAM, and MV chassis. (Photo courtesy of Liquid Spring.)
10 Sutphen Corp. used Hendrickson’s Steertek NXT on the front axle of this pumper for the Harrisonburg (VA) Fire Department. (Photos 10-11 courtesy of Sutphen Corp.)
11 This aerial platform that Sutphen built for the Fort Myers Beach (FL) Fire Department has a Raydan Air Link rear suspension.
The rear axles of most Ferrara pumpers are mostly spring suspensions, VanAlten says, “because if you use an air ride on the rear, it takes up more real estate under the frame and pushes the fuel tank farther back, either extending the truck or taking space away from the compartments. On Ferrara’s aerials, we are primarily using some sort of walking beam suspension, as well as air ride and rubber block suspensions, while the front axles are either flat leaf springs or Steertek NXT suspensions. We’re seeing a lot more air rides on the rear of aerials than we used to, but rubber rides are still the most common because they do well when 90 to 95 percent loaded.”
Carl Harr, director of sales and markets for Liquid Spring, says his company makes several versions of the LiquidSpring® smart suspension. “We make them for Ford, Chevy, International, CV, RAM, and MV (formerly DuraStar) in ambulance, shuttle bus, and motor home applications,” Harr says. “We call it CLASS® for Compressible Liquid Adaptive Suspension System, using a strut with a compressible liquid as the spring/damping medium,” Harr points out. “CLASS has a sophisticated onboard microprocessor that adapts the vehicle’s response to various road conditions, combining a smoother ride with safer handling.”
Harr says the microprocessor monitors and optimizes the ride based on the vehicle’s steering direction, speed, braking level, and motion at each wheel. “Besides a significant improvement in ride quality and handling, it gives the driver more control during evasive maneuvers, less sway in cornering, and less wind sway,” he says. “The system reduces driver fatigue and passenger complaints, dynamically adjusts load balance, and increases the life of the vehicle due to fewer vibrations.”
ALAN M. PETRILLO is a Tucson, Arizona-based journalist, the author of three novels and five nonfiction books, and a member of the Fire Apparatus & Emergency Equipment Editorial Advisory Board. He served 22 years with the Verdoy (NY) Fire Department, including in the position of chief.