A motorhome’s weight, cargo distribution, and tires all play a role in your well-being while on the road.
By Jim Brightly, F385406
Technical Editor
July 2007
In its weight and tire safety program, the Recreation Vehicle Safety & Education Foundation (RVSEF) notes that the three basic elements of safety are attitude, knowledge, and application. One must first make a personal decision that ensuring the safety of one’s motorhome, its occupants, and others is of paramount importance and that one is willing to take measures to achieve this. Attitude may well be the most important factor. After that, understanding the concepts involved and acquiring knowledge is vital. But, knowledge alone won’t keep you safe. You must apply that knowledge and take the necessary steps to verify that you have done all you can to ensure that your motorhome is within its weight limitations, and also that you properly maintain what is perhaps the most vulnerable component when it comes to weight and overloading issues: the motorhome tires.
Why worry about weight? Overloading a motorhome places undue stress on its components and can shorten their life expectancy or, worse still, cause a breakdown or an accident. Major chassis components — including the engine, transmission, brakes, axles, tires, wheels, and frame — are designed to accommodate a specific weight. The lowest-rated component determines the established weight limitations. Performance also can suffer when a vehicle is overloaded, manifesting itself in sluggish acceleration, poor ride and handling qualities, or even dangerously diminished braking capacity.
RVSEF (formerly A’Weigh We Go) has played a vital role in helping to raise awareness within the RV industry about weight safety. Motorhome owners must take responsibility for their role in understanding the various weight ratings and then having their coach weighed and ensuring that it continues to be loaded properly. The best time to weigh a motorhome initially is before you even buy it, so that you can be sure it has the carrying capacity you desire. Then, motorhomes should be weighed as fully loaded for travel.
Understanding Weight Ratings
The Recreation Vehicle Industry Association (RVIA) has adopted a set of standards that are listed on a data label included on each RV manufactured by an RVIA member company. This label provides figures not necessarily included on the federal data plate that must be affixed to all vehicles. In motorhomes, the RVIA data label is located inside one of the coach’s cabinets and/or near the driver’s door “” if there is one. Motorhome owners should be familiar with the following weight terms and their definitions.
Gross vehicle weight rating (GVWR) is the maximum allowable weight the vehicle has been designed to carry, including liquids, passengers, cargo, and the tongue weight of any towed vehicle.
Gross axle weight rating (GAWR) is the maximum allowable weight each axle assembly is designed to carry, as measured at the tires, and including the axle assembly itself. It is determined by taking the lowest applicable rating values of the axle, springs, air bags, suspension, and tires. In other words, the axle is rated according to its “weakest link.”
Gross combination weight rating (GCWR) is the maximum allowable combined weight of the motorhome and an attached towable (car, trailer, etc.). It means that the vehicle’s engine horsepower, its cooling system capability, its transmission, its differential, and its tires have been designed to handle this much weight. It does not mean that the braking system has been designed to accommodate this much weight. The GCWR assumes that the vehicle being towed has its own braking system.
Unloaded vehicle weight (UVW) is the weight of the motorhome as built at the factory, which includes full fuel, engine oil, and coolants. The UVW does not include cargo, fresh water, LP gas, occupants, or dealer-installed accessories.
Sleeping Capacity Weight Rating (SCWR) is calculated by multiplying 154 pounds (an assumed average person’s weight) times the number of sleeping positions as defined by the RV manufacturer.
Cargo carrying capacity (CCC) is equal to the GVWR minus the following: UVW, full fresh water (including water heater), full LP gas, and the SCWR. Dealer-installed equipment and the towed vehicle tongue weight will reduce the CCC. The remaining weight is what can be added in terms of occupants, personal belongings, food, tools, etc. It’s good to know the CCC when purchasing a new motorhome, as it tells you how much weight can be added to the coach and still remain within its GVWR.
Net carrying capacity (NCC) is equal to or less than the GVWR minus the UVW. It represents the maximum weight of all occupants, including the driver, as well as personal belongings, food, fresh water, LP gas, tools, tongue weight of the towed vehicle, dealer-installed accessories, etc. that can be carried in the motorhome. This designation was used on the RVIA label from September 1996 through August 2000, when it was removed in favor of including the CCC and the SCWR.
Although tire weight ratings will not be found on the federal data plate, the manufacturer’s recommended air pressure and (possibly) the tires’ load range are listed there. Follow the coach manufacturer’s recommendations in terms of both pressure and load range. When you check the tires’ sidewalls “” and you should use the same size and load range tire in all tire positions “” you’ll find two weight ratings listed there: single and dual. Make sure the actual axle weight is within the specified weight. If the axle is overloaded, you’ll have to remove and/or relocate the coach’s cargo.
Weighing Your Motorhome
Now that you’ve gained knowledge of weight definitions, let’s discuss how to use your coach’s weight ratings to benefit your safety. As you know, it is your responsibility to know the loaded weight of your coach and the combination weight of your coach and towable, if applicable.
The ideal scenario is to obtain individual wheel weights for your coach so as to ensure that the load is as evenly distributed as possible. RVSEF provides individual wheel weights and an analysis as part of its weighing service at FMCA conventions and most area rallies. One RVSEF finding is that 10 percent of the RVs its teams have weighed exceeded a tire rating without exceeding the GAWR. And owners of motorhomes with air suspension systems especially are encouraged to obtain individual wheel weights. In keeping the coach level, the air suspension system may also create an overloaded tire position that would not be apparent when weighing the coach by axle.
A secondary option is to take the motorhome to a truck stop where it can be weighed for a nominal fee. Look in the yellow pages under the heading “Scales, Public” to locate a certified public scale (one that is inspected regularly by some agency to verify accuracy). Other places that might have certified scales are moving companies, grain elevators, recycling companies, etc. Ideally, look for a scale that permits you to place the individual wheels on the scale. This may be difficult to find since many scales slope downward on the sides for drainage, and this slope throws off the coach’s weight distribution. Similar challenges apply to weighing each side of the coach.
At a minimum, you should be able to obtain three weights: front axle, total, and rear axle. If the scale can’t give you individual axle weights at one time, you’ll have to weigh them separately. As you pull the coach onto the scale, stop with just the front wheels on the scale. Now, move forward until both axles “” or all three if you have a tag “” are on the scale, and stop. Lastly, pull forward until just the rear axle(s) is still on the scale and stop. Don’t worry if the separate axle weights don’t add up to the exact same figure as the total weight; you’d have to know precisely where your motorhome’s fore-and-aft balance point is for these to match. You now have knowledge to assist you in properly loading and distributing the weight in your coach.
The actual gross vehicle weight, or GVW, should be determined with the motorhome fully loaded for travel, including fuel, LPG, water, personal items, and the number of people and pets usually carried. The gross weight shouldn’t exceed the GVWR placed on the vehicle by the manufacturer. If it does exceed this weight limit, the coach will show accelerated wear on all driveline components (i.e., tires, axle bearings, suspension, steering, etc.), not to mention the added risk to your family’s personal safety.
When loading your motorhome, once you’ve made sure it is within its GVWR, you must think about the proper weight distribution. Consider the locations of appliances when you’re filling the cabinets and storage compartments. Use this knowledge to properly distribute the weight from side to side as well as from front to back. When loading, be sure to distribute heavy items evenly throughout. In addition, everything should be placed in such a fashion that it won’t shift during traveling. Improper weight distribution and heavy items shifting while you are driving can have an unfavorable effect on the handling, the ride quality, and the braking capability of your motorhome.
Use the accompanying worksheet to help you find out whether your motorhome is below the weight limitations according to the manufacturer’s data label. Copy the figures from your coach’s data label into the second column. Then enter the actual weight figures in the first column and find the differences. If the actual weight per axle is higher than the label figure, that axle is overloaded. If the total weight is higher than the label figure, your vehicle is overloaded. If the combined weight is higher than the label’s GCWR, the motorhome and towable together weigh more than the vehicle was designed to pull.
Actual Weight Data Label Information
GAW (front): GAWR (front):
GAW (rear): GAWR (rear):
GVW (total) GVWR:
UVW: UVWR:
CCC: CCC:
GCW (total including towable) GCWR:
Tires and Tire Care
Be sure to carefully consider your tire selection. Today’s high-tech radial tire is a very sophisticated device, and with proper care it will give you many miles of excellent performance.
Next, check the age of your tires. The “birthdate” of each tire is molded into its sidewall. Find a string of characters that begins with “DOT.” The last four digits indicate the tire’s date of manufacture. The first two digits indicate the number of the week, starting with week “01” in January and ending with week “52” in December. The last two digits represent the year. So, for example, if a tire was produced in the second week of June 2007, the number would be 2407. Older tires (prior to the year 2000) have only three digits, with the first two indicating the week of the year and the last being the year.
How old is too old? As a rule of thumb, the average life of an RV tire is six years. Factors such as load, the tire’s inflation, sun damage, ozone pollutants, your driving speeds, and frequency of use are just a few of the causes that age a tire. In most cases, motorhome tires need to be replaced because of age rather than wear.
Sun damage can be minimized by covering and protecting the tire with the proper material, but the tire must not be “smothered.” The covering should allow the tire to “breathe.” Most RV shops carry tire covers made from the proper material that allows the tires to breathe while in storage.
Tires should be inspected regularly for excessive or irregular tread wear, bulges, aging, fabric breaks, cuts, or other damage. To prevent damage, remove any nails, stones, glass, or other foreign objects embedded in the tread. If the sidewall looks normal, without excessive weather-checking, examine the tread. Wear bars, which look like narrow strips of smooth rubber across the tread, will appear across the tread when 2/32nd of an inch of tread remains. The appearance of wear bars means the tire needs to be replaced immediately. On vehicles with GVWR in excess of 10,000 pounds, federal regulations require that tires on the front axle be removed when worn down to a 4/32-inch depth; however, to improve traction or vehicle handling, you may want to replace your tires prior to wearing down to 4/32. A tread-depth gauge, available at most large tire outlets, can be used to measure tread depth. This should be done at the beginning of each travel season.
Motorhome tires are subjected to a greater variety of conditions than tires used in automobile applications. Many coaches are stored for long periods of time. You may not know this, but a tire that is used regularly will have a longer life than one that is not. Tires are constructed with compounds that are released within the tire when it heats up from friction on the road. If no heat is being generated, these compounds are not released. Therefore, your tires will dry out more quickly when stored.
Normal, natural aging of a tire, as well as ozone in the air, may cause the rubber to crack, especially in the sidewalls. You should check your tires for cracking or other damage before every long trip. Tires that are more than five years old or ones that show signs of cracking should be inspected regularly by a tire professional to determine whether they should remain in service.
Tire Inflation
One of the most important issues concerning tires is also the most controllable by you: tire inflation. Proper tire inflation pressure is key to protecting the lifetime of tires, especially on motorhomes. Like the relationship between your head and your hat, your tires do more than just support your motorhome. They cushion you over rough surfaces, carry you to new heights, accelerate your body, and “brake” your speed. Clearly, your life and those of your fellow travelers are in the “hands” of your tires, and the only way you can reap the rewards from the engineering that went into your tires is to maintain their proper inflation.
To fully realize its potential and do its job, a tire must have its proper shape or profile. Too little air pressure will cause it to flex too much, creating overheating and stress, which can lead to premature tire failure. However, too much air can be nearly as dangerous. An overinflated tire has a reduced contact area with the road. When you need good contact on the road for braking, especially on wet roads, an overinflated tire could cause you to lose control of your vehicle.
Failure to maintain correct inflation pressures may result in accelerated and uneven tread wear, improper vehicle handling, and excessive heat buildup. To make sure you maintain the correct pressure in your tires, check the air pressure regularly with an inflation gauge that is calibrated up to 120 psi. The recommended inflation pressures for your tires are indicated on the certification label or in your owner’s manual. However, since motorhomes can be configured and loaded in many different ways, the proper inflation pressure should be determined by actual tire loads. The actual loads can be ascertained by physically weighing the vehicle. These loads will change from trip to trip, depending on how the coach is loaded. Check with the tire manufacturer to obtain load and inflation tables.
Inflate all tires on the same axle to the same pressure. Although this may cause a difference in the tire patch (the area of tire tread in direct contact with the ground surface) if your coach is significantly heavier on one side, there are other considerations, such as spring rate, that dictate the same pressure. (The ultimate solution is to balance your coach so that each tire on each axle is carrying the same load.)
Check the air pressure in the tires at least once a month, before each trip, and each morning that you’ll be driving during a trip. Inflation pressures should be checked when the tires are cold; that is, before they have been driven one mile. Heat generated during driving increases air pressure above the proper cold inflation pressure. This is normal, so never “bleed” air from a hot tire, since this could result in dangerous underinflation.
It may be difficult to check the air pressures of the inside tires in dual-tire setups. However, it is important that these air pressures be maintained, because the inside dual tires are subjected to higher heat exposure (from brakes) than the outer tires, as well as lower air circulation and crowned road surfaces (which can cause inside dual tires to support more of the load than the outside dual tires).
Make sure all tire valves and extensions are equipped with valve caps to keep out dirt and moisture. Metal valve caps produce a better and longer-lasting seal than inexpensive plastic caps. Installing a new valve assembly is a good practice whenever a tire is replaced.
Preventing Tire Failure
It is also important to understand how most tires fail. According to Goodyear engineers, obstructions (nails, sharp objects, curbing) are the major causes of tire damage. However, many tire failures are caused by progressive damage. Each mile your tire rolls down the highway overloaded or underinflated, it may be suffering internal damage, something not visible by a casual tire inspection. The day that the tire fails, you may be traveling empty or not moving at all. The tire simply reaches the point where the damage has exceeded its design limits. It may blow out or shed its tread. Of course, tires do not heal themselves, so if they have suffered damage due to underinflation, inflating them to the correct pressure may not prevent eventual failure.
If you do experience a tire blowout, you better have your seat belt on, because it can be a wild and bumpy ride. Your first natural reaction is to apply the brakes “” but don’t do it! Michelin Tire Company recommends briefly pressing the accelerator to the floor (if traffic conditions allow) to regain momentum in the direction you are going and then gently taking your foot off the accelerator. Hold the steering wheel firmly and regain control. If you are on an expressway, gradually move into the far right lane. Immediately turn on your emergency flashers to let traffic around you know that something is amiss. Slow your coach down, without applying the brakes, to 10 to 15 mph before pulling off the road surface.
Tires will wear out faster when subjected to high speeds, hard cornering, rapid starts, sudden stops, and frequent driving on surfaces that are in poor condition. Road surfaces with holes and rocks or other objects can damage tires and cause wheel misalignment. When you drive on such surfaces, do so carefully and slowly. Before returning to normal or highway speeds, examine your tires for any damage, such as cuts or penetrations.
Should you have a tire that continues to lose air pressure, it must be removed from the wheel by an expert for complete internal inspection to be sure it is not damaged. Tires driven even short distances while severely underinflated may be damaged beyond repair.
Punctures up to 1/4-inch in diameter, when confined to the tread, may be repaired by trained personnel. These tires must be removed from the wheel, inspected, and repaired using industry-approved methods, which call for an inside repair kit and a plug (a plug by itself is an unacceptable puncture repair on a motorhome tire). Some punctures may be irreparable.
The repair material used “” for example, a “combination patch and plug” repair “” must seal the inner liner and fill the injury to be considered a permanent repair. Never use a tube in a tubeless tire as a substitute for a proper repair.
When motorhomes are out of service for long periods of time, they should be placed on blocks, not on their leveling jacks. Position the blocks under the axles so that the tires bear no load during the storage period. Do not put the blocks under the frame, because this could cause the suspension to sag or warp over a period of time. Also ensure that the tire-wheel assemblies are protected from direct sunlight. Because inflation pressure will fluctuate with surrounding temperatures, a slight, gradual air loss typically will occur over extended periods. Be sure to inflate the tires, including the spare, to operating pressure before returning them to service.
If you remove your tires from the motorhome, store them in an area that is clean, cool, dry, dark, and well-ventilated with circulating air. Tires should be stored so that the tires at the bottom of a stack retain their shape. If outdoors, protect tires with an opaque waterproof covering.
As noted in this article, so much rides on proper weight distribution and tire care “” both literally and figuratively. Keep an eye on these areas before and during your motorhome travels, and you’ll be able to prevent many potential problems. FMC
RV Safety Training Program
For more information about RV weight and tires, attend the seminars presented at FMCA international conventions and most area rallies by officials of the RV Safety & Education Foundation (RVSEF). This nonprofit organization is dedicated to improving vehicle safety, with a focus on consumer education. Or request a copy of RVSEF’s “RV Safety Training Program,” which features courses on weight, tires, towing, personal safety, propane, fire, driving, electrical, and motor fuels, and includes an excellent video as well. FMCA members may obtain the package for $29.95 plus shipping and handling from the FMCA Store (www.fmcastore.com; or call 800-543-3622 between 8:00 a.m. and 5:00 p.m. Eastern Time, Monday through Friday).
For additional information about RVSEF, visit the organization’s Web site at www.rvsafety.com.
Liquid Weights (pounds per gallon)
Water: 8.3
Gasoline: 5.6
Diesel Fuel: 6.8
Propane: 4.2