Suspension Transformation

Photo Credit: Bob Livingston

By Bob Livingston
June 26, 2017
Filed under Gear, Tech Tips

 

New system using compressible liquid takes ride comfort and handling of motorhomes built on the Ford F-53 chassis to higher levels

For many years, a gas engine-powered Class A motorhome built on the Ford chassis was the only such game in town — and still is today. These motorhomes, perched on Ford’s venerable F-53 chassis, represent the biggest segment in the motorized RV industry. While Ford’s chassis have a proven track record for reliability, the handling traits resulting from underpinnings that have seen limited change over the years are less than stellar.

Compromises are made in a number of arenas to control costs and offer higher gross vehicle weight ratings (gvwr) that can handle larger motorhomes with more amenities in response to customer demand. On the suspension side, leaf springs and shock absorbers are the quintessential components in handling weight and relative driving comfort. But, owners of motorhomes on the Ford chassis have always complained about the rough ride, imprecise steering input and body roll.

Lightly loaded, these motorhomes usually exhibit decent handling characteristics, but once loaded to near maximum gvwr, and especially when heavy items are stored in higher-positioned compartments, body roll becomes much more apparent. Generally, at this point, it’s difficult for passengers to move about while on the road, and the driver will have to maneuver defensively to keep the motorhome on an even keel.

The test motorhome was driven over the shop driveway before and after the installation. Body oscillations were reduced from four to five to just one after the CLASS components were installed.

The test motorhome was driven over the shop driveway before and after the installation. Body oscillations were reduced from four to five to just one after the CLASS components were installed.

A few aftermarket products designed to improve the ride and handling of the F-53 chassis have entered the scene over the years, but the latest from LiquidSpring, called a Compressible Liquid Adaptive Suspension System (CLASS), is destined to change the paradigm of how owners view — and drive — motorhomes built on the F-53 chassis.

The CLASS rear suspension is a five-link system that takes the place of the standard leaf springs and shocks, and uses sophisticated electronics to manage compressible liquid silicone via specially designed struts and control arms — improving stability while reducing road shock and vibrations. To find out how it works, we installed a system in a 2011 Winnebago Adventurer which, loaded to its 22,000-pound fighting weight, exhibited all the negative handling behaviors common with the Ford chassis. The motorhome had 16,261 miles on the odometer.

Handling problems are not new; the auto industry has been working on solutions for more than 100 years. Shock absorbers have been the auto industry’s bread-and-butter solution for years, with air bags entering the scene 50 years ago. While air bags help somewhat, they are still subject to the same tradeoffs between ride quality and handling. Shock absorbers are expected to be the superheroes, but ironically, they can only provide limited control and once they heat up, damping can be compromised.

LiquidSpring ventured into the suspension business while on a mission to smooth out the ride in huge off-road trucks used in underground mining. These trucks were known to shake people uncontrollably, decreasing production due to fatigue and injury. Most engineers were skeptical of compressible liquid, but the company made it work, prototyping a system for mining and other fields that smoothed out the ride so dramatically that it doubled production capability and prolonged suspension life on these big rigs remarkably.

[1]

Before the CLASS components can be installed, the existing leaf springs, brackets, shocks and hardware are removed. Only the factory sway bar remains in place.

[2]

After removing the factory suspension components, the net gain in weight is around 200 pounds; determining axle and tire capacities before the installation is important.

[3]

Design of strut module may look like a conventional hydraulic cylinder, but here the chambers are equally pressurized and react via changes in fluid volume in proportion to load.

[4]

Hydraulic hoses and fittings are commercial-grade and able to withstand many years of rigorous use.

[5]

Holes in the frame are made by a magnetic frame drill, which provides better accuracy.

[6]

Bracket for the track bar is welded to the rear axle. This is where expert welding is important to prevent damage to the axle housing. Track bar

[7]

All other brackets are bolted.

[8]

Track bar prevents lateral movement during up and down travel of the suspension in response to road conditions.

[9]

Upper [9] and lower [10] control arms are mounted to the frame on both sides of the axle, and pivot in response to suspension movement. The OEM sway bar is connected to the rear axle and factory frame rails.

[10]

Upper and lower [10] control arms are mounted to the frame on both sides of the axle, and pivot in response to suspension movement. The OEM sway bar is connected to the rear axle and factory frame rails.

[11]

Secondary fluid volume vessels are attached to each side of the frame and are held in place with loop clamps.

[12]

Hydraulic hoses connect the vessels to the struts through which the compressed liquid is distributed in response to “spring rate.”

[13]

Power module/fluid reservoir [13] with ECU [14] is attached to the frame rail using a special bracket. Hoses are routed from the reservoir to the secondary fluid vessels.

[14]

Power module/fluid reservoir with ECU [14] is attached to the frame rail using a special bracket. Hoses are routed from the reservoir to the secondary fluid vessels. ECU monitors road conditions and sends signals to each strut, via fluid volume, to change stiffness and damping as needed to maintain control and ride quality.

[15]

A single strut on each side is connected to the frame and the control arms. The struts are the heart of the system, which is managed by fluid volume controlled by the ECU. Compressed liquid is not affected by temperature, so damping is consistent on all types of roads.

[16]

Control panel is mounted on the dash where it can be reached easily by the driver. Ride control and height are managed by clearly marked buttons; lights inform the driver of ride mode and in the event of a system problem. Diagnostic codes can be used to troubleshoot the system, if necessary.

While the company’s mining-truck invention taught it how to change stiffness through compressible liquid, there were no electronics at the time to manage the process. Fast forward to 2012 and company engineers found a way to learn the characteristics of fluid using electronics and introduced a product to the bus and ambulance industries that offered dramatic improvements in ride quality. The ambulance industry was actually able to document improvements in patients’ health, which to that point had often deteriorated (fatigued) by adverse vibrations and the bumpy ride to the hospital. Today, 90 percent of these vehicles equipped with improved suspension technology employ the LiquidSpring components, according to the company.

From this experience and success, a new system was developed for the Ford F-53 and cutaway chassis.

To get here, company engineers were charged with understanding what happens to fluid under different temperatures and pressures, and how it flows. In the end, the system had to work harmoniously with the mechanical aspects of a suspension, as well as eliminating the common tradeoffs between ride quality and handling. Sensors used for suspension height, speed, braking and steering input are used to process information through proprietary algorithms that allow the system to react to body roll in milliseconds.

The system has three ride modes: comfort, normal and sport. Comfort bias is toward a better ride, while the sport mode focuses on handling. The controls allow the motorhome to travel in the comfort mode for the best ride quality and will automatically respond to driving conditions, seamlessly changing the spring rate and adjusting load levels (compensating for payload distribution) without driver input. The driver can elect the sport mode, which will stiffen the spring rate regardless of conditions. The driver can also adjust height up to 4 inches using the manual controls on the interface panel that’s mounted on the dash as long as speed is slower than 10 mph.

Installation of the components must be relegated to professionals and although it can be retrofitted to an existing motorhome, the company is focusing on the OEM segment to offer the system from the factory. For testing, we contracted with Redlands Truck and RV Performance Center, Redlands, California, to install the system on the aforementioned motorhome. The Redlands technicians are experts on working on suspensions and are noted for their work on big Class A’s.

Before the new parts could be installed, all the existing suspension components were removed from the chassis, with the exception of the factory sway bar. All the new parts were bolted to the axle and frame except for one bracket, which was welded to the axle. Expert knowledge in welding to the axle is required, since using the wrong technique can result in a damaged axle housing. The parts exchange results in an approximate 200-pound increase in overall weight of the motorhome, most of which is on the rear axle.

The entire process took 30 hours and once completed, the system has a factory-installed look that will make any owner who enjoys gawking at mechanical devices proud. Of course, labor costs can reach $4,500, and added to the approximate $8,000 price of the components, puts the investment at a sizable plateau. The system requires negligible maintenance and is covered by an extensive warranty. Service centers experienced with motorhome chassis are capable of handling repairs, if they become necessary.

Was it worth it? The answer is a resounding “yes!”

Before we installed the CLASS, we set up a test course to establish baselines. The motorhome was loaded for a typical trip and exhibited the typical adverse handling traits that the owner simply tolerated. Right out of the gate, the body oscillated four to five times negotiating the driveway. The factory sway bar is designed to help body roll, but is not compliant enough to do much on the driveways. Once the new system was installed, the oscillations were virtually gone.

On the second part of the course, we drove into an RV park with undulating gravel roads. Rocking back and forth was the most annoying aspect of the drive, with increased body roll while negotiating the turns — even at very slow speeds. Vibrations and suspension shock caused by ruts in the road produced the expected elevated noise level that competed with normal conversations. In this segment, the LiquidSpring system tamed the body roll, reduced noise to a much quieter level and the rocking and bounce were squelched.

Driving on city streets resulted in the most dramatic differences before and after. Dips in the road, especially those in the middle of the turning zone, whipped the motorhome from side to side, throwing around passengers trying to stand in the aisle and/or walk to the rear bedroom. Sitting on the bed was terribly uncomfortable, exacerbated by the constant jarring of the incompliant stock suspension, and trying to sit up straight was virtually impossible when the motorhome was negotiating turns at intersections, even at very slow speeds. Body roll was just too pronounced.

On return visit to the same city streets, improvements in handling and comfort were so good, we thought we were on a different route. Side-to-side movement (body roll) was curtailed dramatically, completely changing the experience for the driver and passengers for the better. The ride was much softer, the jarring just about gone, and walking the aisle was much easier —  and the passengers were no longer launched from their seats. In back, the comfort was improved to a point that sleeping on the rear bed in transit was actually possible without dreaming about being thrown around in a clothes dryer.

The real eye-opener was the ability to aggressively power into the turns, even on roads with dips in the middle of the pavement, maintaining complete control, sans body roll and with only slight bouncing, restoring suspension predictability and driver confidence.

In stock condition entering the freeway on a 90-degree onramp resulted in five oscillations of the body while the motorhome was maneuvered into a straight path; with the CLASS installed, that number was reduced to only one. Steering precision improved and wallowing disappeared, providing a much more controlled feeling for the driver. Jounce on concrete road seams was almost eliminated, making the ride feel like it was on an asphalt surface. Lane changes were much more controlled, with almost no body roll, and powering into sweeping bends in the highway resulted in virtually no driver distress.

While the investment in the LiquidSpring system is sizable, the results make a strong case for those who are on the fence between deciding on a gasser or diesel pusher — or those who love their gas-powered motorhome but don’t look forward to the drive. New motorhome exterior aesthetics, floorplan décor and amenities are closing the gap between the comfort level and livability of a gasser and pusher, and those who find ride and driving comfort paramount often pass on gassers due to the legacy suspension. The LiquidSpring system will change that thinking.

When it comes to improving road manners of the Ford F-53 chassis, the LiquidSpring system over delivers on the results. The CLASS transformation is truly a game changer for owners looking to move Class A gasser ride quality and handling to a higher level.


 

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