Installing closed-cell polyurethane supplemental springs results in a smoother and quieter ride for the Ford F53 chassis
Manufacturers of gasoline-powered Class A motorhomes have a tough assignment: Build nice, comfortable living quarters on a chassis that, for cost reasons, shares suspension componentry found on commercial-truck platforms equipped with four stacks of steel leaf springs – and then make it ride and handle well.
It’s a tall order. Diesel-pusher coaches with full air-bag suspensions may approach luxury road manners, but motorhomes built on chassis equipped with steel leaf springs often need help.
While some owners of Ford F53-based motorhomes may be satisfied, others wish for a smoother ride on rough pavement, and more control of body roll (lean) on curves with the larger, taller profiles – especially if they are loaded to the gross vehicle weight rating (gvwr) or beyond. Front and rear stabilizer (sway) bars are helpful with the body-roll issue, but smoothing out the rough ride has been largely out of reach despite the use of excellent Bilstein shock absorbers.
SuperSprings International of Carpinteria, California, has brought supplemental springs made of closed-cell polyurethane to the RV aftermarket, and they’re relatively easy to install. Products made of open-cell and closed-cell polyurethane are everywhere – sealants, coatings, egg crates, insulation, car bumpers, seat cushions and thousands more, but using this material for cushioning the ride of Ford’s F53 chassis is a game changer.
In the SumoSprings application, varying amounts of nitrogen gas are combined with closed-cell polyurethane to create different compression rates. The outcome is progressive, supplementary springs with a parabolic rate; stiffness that begins moderately as load is added, then grows more rapidly when the springs are compressed by changes in the road surface.
Our installation involved a 2008 Itasca Sunrise (2007 Ford F53 chassis with 22,000-pound gvwr) and the SumoSprings Maxim, the highest-rated spring in the line. The kit part numbers are SSF-180-40-1 front (blue) and SSR-180-54-1 rear (yellow). The springs are bolted onto the motorhome frame and axles, centered above the stock leaf springs.
In preparation for the installation, road height was measured front and rear, chocks were placed fore and aft of the tires, and the motorhome was elevated one end at a time via its onboard hydraulic jacks to provide sufficient access to the frame and axle without having to remove the tires. Heavy-duty jack stands were placed under the frame for safety before the work was started.
The SumoSprings kits include brackets for attachment to the chassis frame and to the axles. The installation required drilling 3/8-inch holes in the frame above the axles, then assembling the necessary brackets with bolts/nuts (supplied) to install the upper and lower brackets on each side, front and rear. The brackets are bolted to the top and bottom of the SumoSprings, and the bottom bracket is bolted to the stock steel spring stack just above and in front of the axle.
The installation involves working in close quarters between the frame and tires, as well as a sharp drill bit to get through the hardened-steel frame.
After lowering the motorhome, road height was remeasured, showing that the SumoSprings had created an additional inch of road height front and rear due to partial compression under static load (motorhome parked).
Prior to the installation, the test motorhome was relatively level, not riding low on its suspension, and it didn’t need the additional road height created by the SumoSprings.Â However, partial compression of the springs without any dynamic loading allowed them to stabilize the ride and handling even on slightly rough pavement.
For a good before-and-after road test, we chose a couple of contrasting routes: the first, a two-lane asphalt road with moderate curves, undulations and patches in the pavement, along with strong crosswinds, and the second, a 150-mile highway that included periodic stretches of broken pavement and rough repairs from having been subjected to heavy commercial truck traffic – a road that we have driven on many times.
While driving the first section with the SumoSprings in place, the effect of the springs was apparent right from the start. Ride quality was noticeably more quiet and controlled, both in terms of road shock felt by driver and passenger as well as the decibel level of squeaks and rattles. We felt less lean to one side or the other (body roll) on curves taken at highway speeds and in driveways, and more predictable handling in strong crosswinds.
On the second test route, our “before” test run had produced a rough and noisy experience on the rougher stretches of this highway. With the SumoÂSprings in place, it was still rough and noisy, although less so. While the SumoSprings cannot transform the ride and handling of a Ford F53-based motorhome into that of an air-bag-equipped diesel-pusher coach, they were capable in this situation of creating a very noticeable – and welcome – improvement in ride quality and stability.
The springs are available for a variety of Class A, B and C motorhomes; Tiffin Motorhomes of Red Bay, Alabama, offers SumoSprings as an option on the company’s gasÂoline-powered motorhomes.
The spring kits for the F53 chassis are listed at $589.50 front and $625.50 rear; installation by a competent mechanic can be expected to take three to four hours. The product’s limited warranty covers 3 years.SOURCESuperSprings International Inc.