The undercarriage of your RV transports thousands of pounds for thousands of miles over various road surfaces, many of which are not in the best of repair. Be it trailer, fifth wheel or motorhome, the unit’s suspension is expected to perform flawlessly regardless of the weight demands we RVers place on it.

Well, suspension failures, such as broken springs, failed airbags and broken or bent trailer axles, do occur. Although most problems can be traced to our own negligence, some attribution should be placed on design specifications and manufacture. More on this later. First, let’s define what a suspension is and review the various types.

Dexter Axle (www.dexteraxle.com), major producers of OEM axles, brakes and suspensions, define a trailer suspension system as providing three basic functions: attaching the axle(s) to the trailer, dampening road shock and cushioning the cargo or load. The majority of suspensions utilize steel springs, either leaf or coil, to provide the cushioning and dampening effect. Some suspensions use a rubberized torsion bar mechanism (Alko and Torflex) in place of springs while others, such as Mor/Ryde, have rubber shear blocks that do the job. Air ride suspensions substitute rubber air bags for springs and require a compressor. Independent suspensions allow each wheel to react to the bumps in the road independently of the other wheels.

Most Class B and C motorhomes usually have an automotive-type independent coil spring suspension in the front with leaf springs in the rear. Most average or entry-level Class A motorhomes will be equipped with leaf springs all round. Class As with air brakes and diesel pushers more often than not will also have air suspension. Shock absorbers are standard on all motorhomes, something that cannot be said for travel trailers and fifth wheels. The "standard" trailer suspension is leaf springs on two axles attached to the frame by front and back hangers with an equalizer on a middle hanger joining the two springs and combining the two wheels on each side of the trailer into a tandem, hence the term tandem axles. Too many trailers and fifth wheels with standard suspensions leave the manufacturing plant without shock absorbers. Shocks provide extra dampening to control excessive bounce and recoil as the wheels encounter road surface anomalies - potholes. Although some suspensions, such as Torflex or Alko, do not need shock absorbers, they are a must on most other suspension systems yet are not included on too many popularly priced trailers and fifth wheels.

At the beginning, I mentioned design specifications. This is the rated weight a particular suspension is designed and built against by the RV manufacturer. The axles used are rated to carry a certain maximum load. The same with the springs and tires. In the building of a fifth wheel for example, the manufacturer marries the frame, axles, springs and tires, i.e. the suspension, to the body of the RV to meet a certain load requirement — the Gross Vehicle Weight Rating (GVWR).

Every RV will have a GVWR listed on the VIN plaque. The suspension underpinning the unit will be designed and built to that exact rating and, in most instances, not a pound more. In calculating the GVWR of a fifth wheel, manufacturers even take into account the amount of weight (pin weight) that will be carried by the pickup to reduce the axle and tire ratings by an equivalent amount. Often you can add up the maximum load capacities of the four tires or the capacity ratings of the two axles and come up with a number that may be, say 1,500 pounds short of the GVWR for the trailer. So, you say, why is this important? Is not the manufacturer showing good production practices and saving money by not "overbuilding"?

Well, for a few manufacturers, yes, but there is still a lot of confusion in the marketplace the RV industry seems reticent to correct. The Cargo Carrying Capacity (CCC) of a trailer is the GVWR less the weight of the full water tank, the weight of the full propane tanks and the weight of the empty trailer. Since 2000, the CCC must be listed on the VIN plaque of every RV sold in Canada. For motorhomes, this also includes an allowance for driver and passenger weights. The problem lies in the fact the literature and specs put out in the promotional material includes the GVWR but, more often than not, does not include the CCC. Sometimes they may use the old term, dry weight, but once again will fail to define it so that it’s not possible to calculate what weight you can safely carry in the trailer and still be within its GVWR. This is even more exacerbated by the trend to more and more slideouts and cavernous storage compartments. Each slideout adds 300 to 500 pounds of weight to the unit. With the average CCC in today’s trailers at about 1,500 to 2,000 pounds, it’s not much of a stretch to attain overload territory by putting just a "few things" in that basement. Our fifth wheel sports a CCC of more than 4,500 pounds. The lightweights and ultra-lites will have a much smaller CCC, many at less than 1,000 pounds, some at 500 pounds.

Coming full circle, the more weight you carry in your RV, the more stress on the suspension and the more it’s going to bottom out with jarring results. It’s a statistical fact more than 50 per cent of RVs on the road are overloaded. If you’re in the market for a new RV, for trouble free suspension performance, pick the unit with the highest CCC in its class. Look for this number on the VIN plaque. Make sure the trailer has shocks and a sturdy suspension configuration. You can order units with greaseable shackles which can prolong suspension life.

For those of us who already have a unit, Dexter recommends that the suspension system be visually checked at least every 6,000 miles for signs of excess wear, elongation of bolt holes and loosening of fasteners. Shock absorbers can be retrofitted on most units. And finally, if you don’t know your CCC or it’s a low value, less baggage may be a good idea.


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Dan Romanko and his wife, navigator Bobbie, are seasoned RVers. The two travel extensively in their fifth wheel. For more information about Dan’s Safe RVing Courses, visit www.explore-canadacaravans.com

Article first printed in RV gazette (March/April 2006). Website: www.rvgazette.com
Copyright 2006 Explorer RV Club - website: www.explorer-rvclub.com Canadian publications mail sales agreement #1435604 ISSN 1484-1339 Published and printed in Canada.