Myriad coach components contribute to your comfort, control, and safety while rolling on down the road or relaxing in the campground.
By Jim Brightly, F358406, Technical Editor
As an old TV commercial used to say, “You ride on a cushion of air.” While it’s true that your tires are filled with air, your motorhome also moves along on rubber (or at least a synthetic compound that goes by the same name), steel, neoprene, grease . . . you get the idea.
The suspension and steering equipment included in this article literally helps to support your RV lifestyle. The use of the items in each category is explained, followed by specific information from manufacturers about their products. Not all coaches employ every one of these components, but many of the products appear on most motorhomes.
Air springs can take more than one guise. An air spring can be a coil-over air bag (as on the front of a General Motors’ P-30 chassis) to support the front of a motorhome; it can be an assist air bag that aids in supporting and/or stabilizing the rear of a motorhome; or it can be the complete suspension (as on many diesel-pusher chassis).
Firestone produces several types of air spring systems: Air-Rite, Intelliride, Level-Rite, and Ride-Rite. Some provide an air-ride suspension system; others supplement the existing suspension system. The Ride-Rite system assists the original suspension system to improve ride quality and handling in a fully loaded motorhome. The air springs’ action is progressive; in other words, as the axle moves vertically, the air spring stiffens in a gradual fashion. In cases where the vehicle sags under load, pressure in each air spring can be increased to level the coach from front to rear or side to side.
HWH produces several different air leveling systems for the motorhome manufacturing industry. The HWH Active Air Suspension is a four-point, electronically controlled suspension system that can provide ride comfort by adjusting the suspension system’s height. For example, according to HWH literature, “When driving a straight, flat road, the settings remain comfortably soft. But when cornering, the system automatically reduces roll by increasing outer air spring inflation and reducing inner air spring inflation, thus maintaining a soft, comfortable ride.” A manual override can be used below 15 mph to raise or lower the vehicle to clear speed bumps, steep driveways, tree lines, etc. A self-monitoring system notifies the driver if a problem arises. The system also can be used to level the coach while parked.
Ridewell RV air suspensions are in use by motorhome manufacturers including Blue Bird, Foretravel, Country Coach, and others on vehicles ranging up to high-end motor coaches.
Axles are used at both ends of the motorhome. With the exception of the GMC motorhome of a few decades ago (it is a front-wheel-drive unit) and the few four-wheel-drive coaches available today, the drive axles are in the rear and the steering axles are in the front. Steering axles are classified as independent front suspension (IFS) or solid axle (usually an I-beam type). IFS uses individual short axles on which the wheels on each side can move independently of one another. On a solid axle, each wheel’s movement affects the other wheel’s movement.
The drive axles have a differential that takes the power from the transmission and converts it to a different direction in order for its internal axle shafts to apply power to the wheels. Virtually all motorhome differentials are “open” (as opposed to “locked” or “limited slip” types) to allow the wheels to travel at different speeds during turning maneuvers when the outer wheel travels a greater distance than the inner wheel.
A tag axle behind the drive axle is included on many large motorhomes to supply the chassis with a greater gross vehicle weight rating than the same chassis could achieve without the tag. However, there are several disadvantages to having a tag axle. One is that it requires two additional tires that will need to be replaced at some point. Also, when making tight turning maneuvers (unless the tag can be lifted off the ground), the tires could be scrubbed, causing accelerated wear. Finally, when driving over soft ground, the tag wheels can accept a greater portion of the coach’s weight, lowering the weight on the drive axle and effectively reducing its traction as well. This can result in the motorhome becoming stuck.
Fabco Automotive Corporation (the axle-producing division of Accuride Corporation) supplies the transportation industry with a broad range of steer drive axles, transfer cases, split-shaft power takeoffs, and other specialty products.
Ridewell is an OEM supplier of axles and suspension systems for tag, steering, and drive axles. The company offers suspension solutions for Ford chassis as well as several custom chassis manufacturers (including drive-and-tag-axle combinations).
Bell cranks are used to support the steering linkage on a motorhome. On the P-32 chassis, the bell crank allows the fore-and-aft movement of the steering linkage coming off the steering gear to be transferred to a side-to-side movement when steering the coach. On P-Series chassis, bell cranks are mounted on each side frame rail (the right-hand unit acts as an idler arm support to the right-side steering linkage). Original equipment bell cranks on a P-Series chassis are equipped with easily worn, permanently lubricated brass bushing bearings. When the bushing becomes worn, steering wheel play is increased. There is a vertical adjustment for end play; however, it doesn’t eliminate side play. On a Freightliner chassis the bell crank acts to support the two-piece drag link used between the Pitman arm on the steering gear and the driver’s-side steering arm.
The SuperSteer Bell Crank is said to reduce steering wheel free-play and minimize constant correction. Two types of bell cranks are used, which accommodate the Chevy/Workhorse P-30 and P-32 chassis, the General Motors G30HD and G3500HD chassis, and the Freightliner XC and Magnum chassis. Both the P-3032 and the SS100 bell cranks offer similar precision engineering that is said to provide tighter steering and longer life than OEM parts. These bell cranks feature a chromoly heat-treated steel shaft and high-tensile-strength casting, spindle, and tapered roller bearings (grease-packed and sealed to keep out dirt and water for life). In addition, unlike OEM bell cranks, these bell cranks can be adjusted repeatedly to return them to like-new performance.
Motion Control Unit
The SuperSteer Motion Control Unit, designed for use on air-suspension coaches, is said to minimize side-whip over bumps, dips, uneven roads, and driveways; reduce sway, roll, and bounce; and stabilize highway ride for comfort and safety. The device is available in different degrees of control for both axles.
The units operate independently, both in the front and back and on each side of the coach. These units act like valves found in many shock absorbers and are said to produce a more smooth, stable ride. The Motion Control Unit should be installed as close to the air springs as practical for best results.
Ride Height Controls
Ride height controls are used in air-ride suspension systems to maintain proper ride height while motoring down the highway. Valves and levers add to or subtract air from the system automatically as needed. On many chassis, when the coach is parked, the ride height control knows to drop air pressure in order to ease access to and from the motorhome’s entrance door. It also can be used to auto level the coach while parked. When the engine is started and the transmission is placed in gear, the ride height control will add air to the suspension system until the proper ride height is reached.
Hadley is said to be a leader in the development and design of ride height controls, with more than 25 years in business and in excess of 1 million valves on the road. A Hadley height control valve is said to decrease recovery times from air dump, to decrease warranty costs, to improve handling, and to enhance overall driver comfort.
Ridewell’s high-performance height control valve for trailers, buses, and recreation vehicles reportedly responds quickly to correct the air pressure and return the vehicle to the desired ride height. The maintenance-free valve is designed with a universal mount to work with all applications. Its features include push-to-connect fittings, quick and accurate operation, and dump and non-dump configurations.
Shock absorbers are aptly named; in fact, their name is also their job. Using hydraulic fluid technology (passing fluid back and forth between two reservoirs through a series of valves) to dampen the vertical movement of the axle without transferring the movement to the coach’s frame and body, a shock absorber transfers the energy of movement to heat, and then dissipates the heat to the air passing over its outer surface.
The tube of a Bilstein gas pressure shock absorber is fabricated using a special extrusion method. This process achieves a tight peak-to-valley tolerance and maintains consistent wall thickness. Bilstein’s seamless monotube design eliminates performance-robbing cavitation and is said to provide high tube strength while maximizing heat dissipation and shock life. The new “comfi-track” piston head design allows independent tuning of the compression and rebound damping forces while reducing high-frequency inputs such as expansion joints to provide excellent ride comfort and performance.
Koni’s new shock absorber is known as the Frequency Selective Damping (FSD) shock. The FSD design allows it to adjust according to road conditions. Each FSD shock has two parallel oil flows: one that travels through the piston assembly, and another that travels through an FSD valve. The FSD valve is pressure-sensitive, and will close only if the shock extends for a prolonged period of time. When you hit a small bump such as an expansion joint, shock oil can flow easily through the FSD valve, providing a smoother ride. However, if your motorhome starts to bounce, the FSD valve closes and forces the shock oil to travel through the piston assembly, controlling the bounce and sway.
Springs come in two types: coil and multi-leaf. Coil springs are made from steel rods that are heated and then wrapped around a central core. The rod diameter and the tensile strength of the steel used in the production of the coil determine the weight rating of the coil. Leaf springs are made from strips (or leaves) of what is called spring steel, so named because it is flexible, not brittle, and tends to return to its original arc. The main leaf has rolled ends to accommodate attachment points. A center pin in each “stack” of leaves slips through a hole in each individual leaf to keep the leaves centered over the axle. Two or more end clamps on each stack hold the leaves in alignment, preventing them from spreading out from the center pin like a pair of fans. In many cases, the spring manufacturer will slip Teflon or plastic shims between the leaves to keep them from squeaking or binding.
Springs, regardless of their design, do not control rebound in the same sense as shocks do. Springs are there to support the weight of the coach and to minimize or eliminate the transfer of movement from the axles to the chassis, and thus the coach. Without shocks to absorb and control spring rebound, springs could continue to oscillate for some time after each roadway obstacle.
Leaf springs also are used to align the axles to the chassis frame, which is why they are used more extensively on solid axles than coil springs. Multi-leaf springs are solidly attached to the frame at one end through a soft bushing. This attachment point becomes the pivot point of the spring. The other end is attached to the frame via a shackle with two bushings, which allows the spring some leeway in movement, thereby lengthening the spring’s duty lifetime. The distance between the spring’s center pin and its pivot point controls the axle alignment.
Coil springs, when used on solid axles, require several additional hardware items to maintain axle-to-frame alignment: track bars (control axle twisting), upper and lower control arms (control axle fore-and-aft alignment), and linking arms (control axle sideways alignment). When used on a double A-arm suspension “” as on the front of a P-30 chassis “” coil springs simply support the weight of the coach.
As you can see, because of the number and precision requirement of the added components needed for coil springs, it’s much cheaper to use leaf springs than coils. However, the consensus is that coil springs produce a better ride. As they say along the midway, “You pay your money and you take your chances.”
SuperSteer Coil Springs are designed to correlate to the actual weight of a motorhome. These heavy-duty springs support the true axle weight of the coach. According to company literature, that means drivers experience less bottoming out, get a better handling motorhome, and experience longer tire life. They are designed for Chevrolet/Workhorse P-Series chassis, Chevrolet P-32 chassis, and any type A Chevy motorhome that uses air bags and has an independent coil spring front end.
A steering control unit’s function is to control rebound and bump steer in the steering control assembly in much the same fashion as a shock absorber controls spring movement. In fact, most steering stabilizers look a bit like shock absorbers.
The Blue Ox TruCenter Steering Control is said to add safety with its front tire blowout protection, and allows the center position of the steering to be adjusted while going down the road. This adjustment permits the driver to customize the steering to compensate for crosswinds and road ruts. These steering performance enhancements are said to help reduce front tire and front end wear, which helps slash maintenance costs while also improving driver comfort and lessening driver fatigue.
The SteerSafe Steering Stabilizer is installed on the front end of the motorhome and helps to ensure driver control. The SteerSafe unit is said to guard against violent chassis reaction to front tire blowouts, potholes, soft shoulders, high winds, wandering, accidental encounters with curbs, and highway medians. It also helps reduce driver fatigue.
The Safe-T-Plus Steering Control Device is a mechanically assisted, hydraulically dampened, positive-centering system. That’s engineer-speak for saying Safe-T-Plus helps keep the coach on the straight and narrow even if it encounters a surprise front blowout, side wind, pothole, pavement drop, road rut, or curbing. The driver maintains control and steers straight ahead.
Controlling body roll is a team effort. As noted earlier, shock absorbers control and reduce up-and-down motion; antisway bars “” or, as they are more commonly called, “sway bars” “” reduce side-to-side sway by using the weight of the axle assemblies to counter the coach’s motion. Adding a set of antisway bars to your suspension system will have the same effect on sway as a good set of shocks has on vertical motion. A driver will immediately notice an improvement in stability and tracking, especially on curves, on highly crowned roads, or in brisk side winds.
The Amtech Corporation RollGard Suspension Stabilizer is reportedly an easy-to-install, cost-effective solution to motorhome handling issues such as excessive sway, lean, and bounce. Mounted above and parallel to the vehicle’s existing leaf springs, RollGard exerts constant opposing pressure to the leaf spring pack, preventing it from overextending and then violently rebounding. Held in place by its own tension, the RollGard requires no drilling, welding, or modification to install, and its patented design incorporates a roller shackle assembly that will not bind or squeak. Designed for universal fit, the RollGard Super Duty, with its wide, 4-inch steel shackle, is applicable for type A motorhomes, while the Heavy Duty model fits most type C motorhomes.
Roadmaster’s RSS Anti-Sway Bars have a thicker diameter than the original-equipment antisway bars they replace. According to Roadmaster, a 1/4-inch to 3/8-inch increase in diameter can have a large effect on performance. On average, torsional roll stiffness is increased by 30 percent for each 1/8-inch increase in diameter. RSS antisway bars have polyurethane bushings, which, unlike the rubber used in stock bushings, are impervious to gasoline, oil, and ozone corrosion. Polyurethane is more resistant to abrasion and doesn’t buckle under heavier load weights.
Track bars are designed to keep the drive axle properly aligned with the frame by eliminating axle side-to-side movement without affecting its vertical movement or supporting any of the coach’s weight.
Blue Ox’s TigerTrak eliminates side shift of the axle in relation to the frame of the chassis on the coach. This shift gives the sensation of movement that the driver of the coach tries to correct by turning the steering wheel, which can result in oversteering and actually worsen the situation. This unwanted movement of the axles and oversteering can give the feeling of instability and lead to driver fatigue. No drilling or welding is required for installation. Applications include Chevrolet P-Series chassis and type C chassis, Ford type A and C chassis, Kodiak 4500 and 5500 chassis, and Workhorse W and P-Series chassis.
Roadmaster Davis TruTrac bars are designed to eliminate wander and reduce rut-tracking by controlling excessive axle side play, without preventing normal up-and-down suspension travel. The benefits are said to be predictable handling, an immediate improvement in both vehicle performance and safety, and increased driver comfort “” more positive control means less driver fatigue. Each TruTrac bar comes complete with all mounting hardware, and installs using predrilled factory holes “” no drilling or welding required. They reportedly will not interfere with any factory original equipment, or affect any factory warranty. Davis TruTrac bars are available for Ford F-53 (V-8 and V-10) and all Workhorse motorhome chassis (W16, W18, W20, W22, and W24), as well as Chevrolet Kodiak 4500/5500 chassis. Davis TruTrac bars are cadmium-plated and use polyurethane bushings for maximum stability and longevity.
According to product literature, SuperSteer Rear Track Bars help eliminate uncontrolled rear axle side shift “” known in the industry as the “tail wagging the dog” effect. The bars are said to eliminate side-to-side shift, allowing the driver to feel less stress while driving in a strong wind and release the tight grip on the steering wheel when a semi-truck is approaching. Installation is strictly bolt-on “” no drilling or welding is required.
Because much of the equipment mentioned in this article is not sold directly to consumers, only a contact telephone number and a Web site for each company is listed (no address). This information will allow you to contact the manufacturer and find a dealer near your location, if necessary.
Amtech Corporation – sway bars (888) 880-8949; www.amtechsprings.com
Bilstein – shock absorbers
West, (858) 386-5900; Bilstein – East, (704) 663-7563; www.bilstein.com.
Blue Ox – steering stabilizers, track bars; (888) 425-5382; www.blueox.us
Fabco Manufacturing Corporation – axles; (800) 967-8838; www.accuridecorp.com
Firestone Industrial Products Company – air springs; (800) 888-0650; www.firestoneindustrial.com
Hadley RV, Transit & Specialty Vehicle Unit – ride height controls; (574) 293-5669; www.hadley-products.com
HWH Corporation – air springs; (800) 321-3494; www.hwhcorp.com
Koni – shock absorbers; (859) 586-4100; www.koni.com
Ridewell Corporation – air springs, axles, ride height controls; (877) 434-8088; www.ridewellcorp.com
Roadmaster Inc. – sway bars, track bars; (800) 669-9690; www.roadmasterinc.com
Steer Safe Inc. – steering stabilizers; (800) 845-5504; www.steersafe.com
SuperSteer – bell cranks, motion control unit, springs, track bars; (888) 898-3281; www.supersteersuperstop.com
United Safety Apparatus Inc. – steering stabilizers; (800) 872-7233;