Motorhome Tire Load and Inflation Ratings
By John Anderson, Founder,
RV Safety & Education Foundation
Sometimes it takes a tragedy to wake us up to something that we should have been concerned about but just never
considered a priority. After all, bad things happen only to other people. Right?
After weighing more than 30,000 RVs during a thirteen-year span, I can tell you with confidence that a significant
number of motorhomers are traveling down the road on overloaded tires that could fail at any time, with potentially
catastrophic results.
Finding the ratings
Tires, like most manufactured products, are designed to operate within a specific load; we call this "tire load rating." On
the sidewall of your motorhome's tires you will find a rating for a single application (the front axle or tag axle of your
motorhome) and a dual tire rating (usually the drive wheels).
Each rating is accompanied by an inflation pressure that, if used, will give you the stated rating. This does not mean that
this inflation pressure is correct for your motorhome. Because RVs can be configured and loaded in various ways,
inflation pressure must be set based on the load being carried by the tire, if you wish to achieve optimum life and
performance from you tires.
Every tire manufacturer publishes load/inflation tables for their products, which provides us with this critical information.
Also, remember that the specified pressures are cold pressures; in other words, pressure in the tires before the tires
start rolling down the road and heat becomes involved.
Understanding motorhome loads
I suspect that many motorhomers already understand basic tire rating information. Where I fear the message is being
lost is in the manner in which we use the load-inflation tables. We need to recognize that motorhomes are not built
symmetrically. Of all the RVs we've weighed, we've never come across one that was loaded equally on both sides.
Motorhomes are equipped with slide outs, generators, refrigerators, holding tanks, fuel and water tanks, and much
more. The only way to properly weigh a motorhome to ensure that you are within your tire ratings is to weigh it by
individual wheel position. Once you have done this, you can refer to the load/inflation table to determine the correct
inflation pressure for your tires.
If the load on a tire is greater than the maximum rating shown on the sidewall, you must correct the situation. This can
be done by reducing the load on the tire, either by unloading or redistributing the equipment in the coach, or by
upgrading to tires with a higher load capacity.
Load ranges
Tires come in many different load ranges, so it may be possible to change to a higher-load-rated tire within the same
size. If you do so, be sure not to exceed the load rating of the wheel. If you change tire sizes, make sure you consult an
industry expert to ensure that proper fit and vehicle compatibility are maintained.
Keep in mind that installing tires with a higher carrying capacity solves only the problem of tire overload. It does not
increase the gross axle weight rating, and does not resolve issues related to the overloading of other components --
axles, suspension components, etc.
Reading inflation tables
Be certain that you have the correct load/inflation table for the manufacturer of your tire. Different tire manufacturers
use different specifications. For example, a Michelin table designed for most sizes larger than 16 inches cannot be
applied to other manufacturers' tires. If the tire size matches and the data on the far right of the table for your load
range matches the information on the sidewall of your tire, then you have the correct table.
On the table, find the load you measured on the applicable line, dual or single, and move up to the corresponding
MINIMUM inflation pressure for that load. Since your motorhome weight varies considerably with fuel, water, groceries,
etc, it is important that you weigh your unit in its heaviest configuration, or how you normally travel. Since inflation tables
give us the MINIMUM pressure to carry the load, we suggest that you move one block to the right on the chart, or 5 psi,
to give yourself a safety margin. If you find that your load exceeds the chart rating, address the cause -- your coach
weight. Do not try to compensate by straining the capacity of your tires.
Axle loads
Expect to find a different load on each side of the axle. It's important that all tires on the same axle be inflated to the
same pressure, based on the heavier side. If doing so results in an over inflated tire on the light side, correct the
situation by balancing your coach.
An over inflated tire has reduced "tire patch," or contact with the road, and may result in unsatisfactory braking,
particularly on a wet road. If you're unable to configure your coach so that it does not exceed a tire rating, contact your
motorhome dealer or manufacturer immediately and ask for assistance. They do not want your safety to be at risk, but
keep in mind that your safety ultimately is your responsibility.
Air suspension chassis
Our data indicate that 11 percent of all of the motorhomes we have weighed exceeded a tire rating without exceeding an
axle rating, which means that a tire overload would not be detected on a truck scale when the coach is weighed by axle
only. However, almost 50 percent of some motorhome models with air suspension exceeded a tire rating, and it is not
uncommon for us to find tires that exceed their rating by more than 1,000 pounds. This will virtually guarantee a tire
failure.
If you have a motorhome equipped with air suspension and have not weighed it by individual wheel position, I urge you
to do so before your next trip so as to verify your safety.
If you have been advised to select your tire pressure based on ride quality, how hot they feel to your touch, how the
tread wears -- or anything other than measuring the load on your tires to ensure that you are not exceeding a tire
limitation -- the advice is not in the best interest of your safety.Tire durability The RV Safety & Education Foundation
sponsors RV safety programs and conducts educational seminars.
Weight & Tire Safety
By Jim Brightly, F385406
Technical Editor
A motorhome’s weight, cargo distribution, and tires all play a role in your well-being while on the road.
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
Tire Load and Inflation
