by Peter M. Greig
As a Technical Advisor at this web site, I am frequently asked questions relating to the weight of RVs, towing capacity of trucks, and other questions relating to the weight and loading of RVs, trucks and trailers. In response to these many questions I find I am sharing the same information and advice with one RV'er at a time. The similarity of the questions has prompted me to write this article so that I can share my education and experience with a wider audience.
I am a staunch advocate of SAFETY in the RV community. With over two-million safe miles under my belt (well o.k., I'm not an expert on anatomy) I must be doing something right. Also, with nearly ten years experience as a volunteer firefighter, I have picked through the consequences when things go terribly wrong. Because the members of the RV community come from such diverse backgrounds no one can reasonable expect everyone to be "all knowing" in all aspects of our lifestyle. One of the wonderful things about RV'ers though, is that we love to share expertise in areas with which we are familiar. In that way we can all benefit; we can all be SAFE, and that is my intent with this article. By making informed purchasing decisions, and putting SAFETY first, we have the power to change the industry. If we don't buy junk or mismatched units, manufacturers will stop making those units that do not sell. That is the way we can ensure that SAFETY is improved and we get the products we want and need, rather than what some corporate entity thinks they can make money with. PMG.
A critical safety issue all RV'ers need to be become more informed about is "Weights & Balance". But, just what is meant by "Weights and Balance"? Why is this term becoming of more interest to RV'ers? The answers are fundamental; Saving time and money, and safety! Saving you time and money, and ensuring your safety. Pretty solid reasons for most of us to realize the importance of Weights and Balance, not as a fad, but for survival.
"Weights & Balance" pertains to the weight of an object with all of it's component parts, and the distribution of that weight. Although weight and balance applies to many fields, I will limit the discussion to RVs. Building on the fundamental definition the discussion will include matters such as Gross Vehicle Weight Rating (GVWR), Gross Combined Vehicle Weight Rating (GCWR), Axle Weights, Axle Weight Rating (AWR) and more.
Proper loading of, and weight distribution in, your rig can prevent premature tire failure, suspension problems, broken axles, burned-up transmissions or differentials, and other breakdowns. In addition to the cost of repair parts and labor, there could be expensive unscheduled stays in hotel/motel rooms, and the associated meals, towing, etc. Of course, the worst case scenario would be a wreck resulting from a blowout, or perhaps loss of control.
There is a difference between "load" (actual weight applied) and "load rating" (maximum engineered design load limit). Gross Vehicle Weight Rating (GVWR) is determined by the manufacturer in the design of the unit. GVWR cannot be changed; that is to say, the addition of heavier components does not change the legal GVWR of your vehicle. Any load exceeding these manufacturer's rating values is both unsafe and illegal; and perhaps immoral, for in doing so you consciously put other people at risk of life and limb.
For a long time there has been extensive discussion, even heated debate, concerning the Weight Rating tags affixed to Recreational Vehicles by the manufacturer. The industry is being responsive to consumer demands for accuracy, but the consumer and the manufacturers still must reach understanding of what the weight rating terms are describing. The Recreational Vehicle Industry Association (RVIA) requires all member manufacturers to properly label each RV that leaves the factory. However, this is voluntary compliance and not all manufacturers are association members. There are many RV enthusiasts that don't have either the knowledge or the training to interpret weight ratings. Nor should they have to if they could depend on the salesperson to candidly represent the product. That salesperson should be ready to inform a customer if they are making a bad choice. The discussion of the RV load matching the chassis' or tow vehicle's capacity needs to take place during the sales process. We, the consumer, need to be responsible too, and not be impulsive or unrealistic in our expectations or demands. We must educate ourselves about what all the numbers on the nameplate mean. If your intended purchase is too heavy for your tow vehicle or chassis you will be faced with continued frustration, frequent major (read that as expensive) repairs, and in general a frustrating and expensive long term proposition, instead of the fun and relaxation that the RV Lifestyle should be. The following terms do not have consistent usage in the RV marketplace. Have a discussion with the salesperson to understand exactly how they are using these terms.
Dry Weight is the empty weight of the vehicle or trailer. Dry weight may or may not include the weight of appliances, slide outs, etc.
Wet Weight is the weight of the vehicle with fuel, oil, and coolant onboard. Wet weight should, but may not, include the weight of the LPG (propane or butane) in the tanks, and fresh water. (Water weight is 8.34 lbs./U.S. Gallon so a 100 Gallons weighs 834 lb..)
Curb weight, or Net Weight should be the weight of the unit as it is sitting on the lot, without the personal load you will be adding.
Payload Capacity is the difference between the actual weight and the GVWR of the vehicle or trailer. Options and accessories may add weight that is taken from the payload capacity, leaving you with less margin than you think you have. Ask the dealer to provide proof of the units weight before you finalize the sale. Then do the math and calculate what the remaining payload capacity really is.
Gross Combination Weight Rating (GCWR) is another design capacity of a towing vehicle. It means the maximum weight rating of a towing vehicle and a towed unit in combination. GCWR takes into consideration such things as the drive train capacity (i.e. engine, transmission, drive shaft and differential), gearing, braking capacity, suspension, and axle loading. When integrating a tow vehicle with a trailer, either a fiver or travel trailer, add the GVWR of the trailer with the GVWR of the tow vehicle. If they add up to more than the GCWR of the tow vehicle it a bad match. The only solution is to pick a lighter trailer or a bigger tow vehicle. The same applies to a self contained unit and a towed unit, either four wheels down or on a dolly. Each of the big three pickup truck manufacturers (Chevrolet, Dodge and Ford) state in their literature a "Trailer Towing Capacity" as well as an alternate method for determining maximum allowable trailer weight. The published towing capacity is maximum allowable trailer GVWR, but usually requires extra optional features - called a towing package, and other options such as a particular engine or rear axle ratio. In addition,
State Laws require that any towed vehicle exceeding a specified weight, usually about 1,000 to 1,500 lb.., must have it's own braking system. The alternate method for determining allowable trailer weight requires that you know the loaded weight of the tow vehicle and the loaded weight of the trailer (something we don't know when we are on the dealer's lot). The sum of these loaded weights must not exceed the tow vehicles GCWR. If you use the alternate method for computing allowable trailer weight, you risk not being able to load the tow vehicle more than the weight you used when you calculated the allowable trailer weight. There are also limits placed on the tongue or "hitch weight" when towing a travel trailer. Plan on 12% of the trailer's GVWR as hitch weight; actual hitch weight when connected should fall between 9% and 12% of the trailer's loaded weight. Fifth-wheel pin weight comes out of the trucks payload capacity, and you should plan on 18% of the fiver's GVWR. With the fiver hitched-up the pin weight should be between 15% and 18% of the trailer's loaded weight. No combination should ever exceed the tow vehicle's Gross Axle Weight Ratings, front or rear.
All RVs have wheels, tires and axles in one form or another. Tires have ratings for weight load, inflation, temperature, speed, rim width, rim spacing for dual wheels, etc.. Axles have weight ratings (some light ones even have speed ratings). The tires on a particular axle need to be inflated to the pressure specified for that weight load by the tire manufacturer. Proper inflation extends tread life, prevents tire overheating, and improves fuel economy by reducing rolling resistance. Understand that all tires on a vehicle may not need the same inflation pressure, but all tires on the same axle do. The tires on the front axle can require a different pressure than the rear axle, which can be a different pressure than the trailer tires. The key point is that each tire needs to be inflated to the correct pressure for the axle load it is supporting. Tire manufacturers publish ratings for their tires; ask your tire manufacturer's dealer for a copy of the table of "Inflation Pressures Vs Weight Ratings" that apply to each tire size and model on your rig. Check inflation pressure when the tire is cold; that is, before it is driven more than a mile; not less than three hours after you have stopped driving; and, not after the tire has been exposed to direct sunlight long enough to cause a temperature rise inside the tire. Double check the accuracy of your tire gauge every six months. Most tire dealer's shops have a "Master" tire gauge you can check your gauge against. I favor the use of a digital gauge that can be calibrated to atmospheric pressure before each use, but even these should be verified periodically.
You have probably already seen articles relating to weighing your rig; front-to-back and also side-to-side. This is an important task to take care of when you first acquire and load your RV, whenever you change equipment that could affect the vehicle's weight (RV and/or Tow Vehicle), and periodically thereafter - the "period" depends on how much you travel. If necessary, reconfigure your rig, or reload it, and then have it weighed again. You may have to repeat the process until you get the weights within required limits and distributed correctly. It is surprising how much weight distribution changes just through usage. Things get stowed in different places; new things are acquired as you travel, some things are used up or taken out, etc. "Weights and Balance" is dynamic; that is, it changes.
Front-to-back distribution of a two axle, six-wheel "straight rig", that is a non-towing vehicle, when loaded, should be 30% on the front axle and 70% on the rear axle. For a towing vehicle of two axle, six-wheel configuration pulling a 5th wheeler as a semi-trailer, the ideal distribution would be 20% GCW on the front axle, 40% GVW on the rear axle, and the remaining 40% GCW on the trailer axles, however, practical distribution is 15% on the front axle, 31% on the rear axle, and the remaining 54% GCW equally divided on the trailer axles. A rig that is not relatively equal side-to-side will not ride or handle well. If there is an out of balance condition in either direction (absent a broken suspension component or flat tire) it is due to improper load distribution. Side-to-side imbalance could be either the result of incorrect loading or poor manufacture. Strong evidence why it is best to weigh before you buy.
Most travel trailers should use a load leveling (weight distribution) hitch. Before hooking up measure the distance from some convenient reference point on the tow vehicles front and rear bumpers to the ground. Then connect the trailer and start loading the hitch torsion bars one chain-link at a time, keeping the chains equal on each side. As the load on the torsion bars is increased, the rear of the tow vehicle comes up and the front goes down. When the front and rear bumpers are as close to the reference measurement as you can get (and it should be within a half-inch at the front bumper) the hitch is tensioned correctly.
A self-contained unit's wheelbase to length ratio can be used to judge how well a vehicle will ride and handle. A short wheelbase makes for easier maneuvering while a longer wheelbase increases high speed stability and ride comfort. However, when comparing Length Overall (LOA) to wheel base length, a long body on a short wheel base is not desirable.. Dividing the wheel base (Inches) by the vehicles length (Inches) it is favorable to have a ratio of 0.54 (54%) or more. Long haul busses, such as Greyhound buses, have a 0.66 ratio for both comfort and SAFETY. Yet another issue is the center of gravity. The higher the CG the less stable the vehicle will be in turns and curves, or in cross winds. Calculation of the CG is complex; so ask the manufacturer to provide this important data.
No matter how many times you may have gotten away with improper vehicle integration or overloading in the past, or what you may have seen others doing, to be SAFE you need to respect the engineering design limits. These ratings are based on a lot more than what I can cover in this article, but the bottom line is expressed as the weight ratings published by the manufacturers. Be safe - live by them.
Note: RVers Online is indebted to Peter Greig for this outstanding contribution to the literature of RV Safety...