Taking care of your coach’s tires will help them last longer and contribute to your safety.
By Peter D. Du Pre
On the whole, I’d have to say that we RVers are by nature a finicky lot. We keep our rolling homes neat, clean, and running right. In fact, visit any RV park and odds are that you’ll see more than a few people cleaning, tuning, and generally caring for their coaches. According to industry professionals, however, there is one area of maintenance in which most RVers could improve: tire care. RVers tend to overlook the issue of proper tire care, which is both foolhardy and dangerous. Not keeping your motorhome tires in tip-top condition costs you money and could potentially cause a tire failure and an accident.
Although a variety of factors can contribute to tire failure “” such as prolonged exposure to the sun’s ultraviolet (UV) rays, overloading, uneven weight distribution, suspension problems, and misalignment “” the main cause is improper inflation. Overinflation or underinflation will cause excessive tire wear and can lead to blowouts. While both conditions will put extra strain on the tire structure, underinflation is far and away the critical maintenance issue facing RVers today. In fact, a recent survey conducted by Bridgestone/Firestone showed that four out of five RVs had at least one underinflated tire, of which at least a third were dangerously low on air pressure. In addition, a survey conducted by the Recreation Vehicle Safety Education Foundation (RVSEF) found that almost 40 percent of RVers say they go six months or longer between inflation checks. Apparently, many RV owners don’t understand the importance of proper inflation and the relationship between inflation and the load-carrying ability of their unit.
Why proper inflation is important
Improper inflation affects the motorhome owner in a variety of ways. First and foremost, there’s the safety issue. An underinflated tire is not able to sustain the load of a properly inflated one, and it effectively is overloaded even if the motorhome is not overloaded. It flexes too much and causes excessive heat buildup within the tire, which can lead to failure, sometimes a catastrophic one. It will handle poorly, wear quickly and unevenly, and the increased rolling resistance will decrease fuel economy. Often the underinflated tires are the inner tires on a set of duals. These tires can be difficult to check for inflation. The problem is that a catastrophic failure of an inner tire can mean the failure of the outboard tire as well, and that can lead to a loss of vehicle control. Having underinflated tires also means increased stopping distances and poor vehicle handling.
Overinflation is not as bad; in fact, according to Toyo tire engineers, overinflation has really never created a problem. However, overinflation may accelerate tire wear because as the air in the tire expands, it heats up, putting extra pressure on the interior of the tire. Add the weight of an overloaded coach and you have a prescription for a blowout. Blowouts usually occur when a tire is under prolonged stress “” as when driving at high speeds on the freeway “” and a tire failure in heavy traffic and at high speed can be a real disaster. Overinflated tires may also be more likely to fail from the sudden impact of hitting a pothole, because they flex less and are more likely to be punctured by road hazards. Overinflated tires also have a smaller contact patch (the part of the tire tread in contact with the road) than a correctly inflated tire, which means that traction and handling will be adversely affected, along with braking ability, especially during inclement weather.
A second personal impact of improper tire inflation is the cost. Tires that run with the wrong air pressure experience irregular and rapid wear. This not only means more frequent tire repairs and replacement, but it also can cause increased wear and tear on suspension and steering components. And let’s not forget the cost of fuel. Running overloaded/underinflated tires results in a decrease in fuel economy by as much as 10 to 15 percent. Add up the cost of extra tire repairs, replacing tires, repairing suspensions, and a decrease in fuel economy, and you’ll find it can easily come to a few thousand dollars every year or two. That kind of money will pay for a cross-country vacation!
How do tires lose air?
Apart from the obvious reasons for air loss, such as small holes, bad valve stems, or loose valves in the stem, tires lose air through a process called permeation. Over time, some of the air molecules in the tire will permeate the rubber, escaping into the atmosphere. Even a properly mounted and inflated tire may lose around one pound of air pressure per month “” possibly more during hot weather. If you are one of the 40 percent of RVers who go six months between tire pressure checks, it means you could have lost up to 6 psi since the last check, and your vehicle may be dangerously overloaded and experiencing rapid tire wear. Factor in a slowly leaking valve stem or a small pinhole in the tread, and air loss can be even greater.
In order to get the most miles out of your tires, plus have optimum safety, handling, and economy, it is vital to keep the tires properly inflated and in good overall condition. This is easy and inexpensive to do, takes only a few minutes a week, and costs almost nothing.
The first thing you must do is to buy a quality tire gauge. Don’t rely on the air gauges at most fuel stops; they are notorious for being inaccurate and can be off by as much as 5 psi in either direction. Likewise, the $2 pencil-style gauges sold at auto-parts and discount stores are woefully inaccurate. Using a tire iron, mallet, or bat is also extremely inaccurate. Your tire may sound great when you whack it, but that won’t tell you anything. Also, don’t depend upon eyesight. Modern radial tires look pretty much the same when they are correctly inflated and when they are 30 percent underinflated. Only a pressure gauge can give you a correct reading.
Use an accurate dial or digital gauge that is calibrated to more than your tires’ maximum rated pressure “” some engineers recommend at least 120 psi “” and make sure it has a double-ended foot so you can fit valve stems from two angles. Choose a resettable model that “remembers” the air pressure reading until you reset it. You can buy one at an auto-parts store, RV supplier, or truck stop for less than $20 and it will pay for itself within six months if used on a regular basis.
The amount of use your motorhome sees is what determines how often you check the air pressure. For vehicles in storage, you need to check and adjust tire pressures once a month. Vehicles that see frequent use need a pressure check and adjustment once a week, and every morning when driving on trips. Make sure you make it a point to check your spare, too. Like the other tires, the spare also loses air through permeation and is all too often ignored, meaning that it may be underinflated just when you need it most.
Accurate pressure readings can be obtained only when the tires are cold, so the best time to check the tires is before starting out in the morning. You can drive the vehicle to an air pump if the distance is no more than about a mile. Any farther and the air in the tires heats up, making your reading inaccurate. If you must check the pressure at other times, make sure the vehicle has been parked at least three to four hours and that the tires are shaded, as direct sunlight can significantly heat up the tires.
As you check the tires, take the air hose with you so you can “top up” on the spot. When you add air, make sure it is exactly the right amount to bring the tire up to the vehicle manufacturer’s required pressure spec. This is an exact science, and being close is not good enough. You need good load-carrying ability, road-gripping ability, and even wear. Only the correct pressure will do this.
Don’t forget to check the inner tires on dual axles. Inside tires fail more often than outside tires, because they are not pressure checked or inspected as often. These tires are not “spares.” They need to carry exactly the same air pressure as the outer tire. In addition, all the tires on the same axle should carry the same air pressure. On inside tires it can be difficult to get a pressure gauge on the stock valve stem. If this is the case on your coach, have tire stem extensions added so you can easily check the pressure. Try to mount the valve stems 180 degrees apart so you don’t get them mixed up when checking air pressure and adding air.
Whenever you check air pressure, take a couple of extra minutes to inspect the tires. Check them for nicks, cuts, nails, cracks, chalking, chunking, bulging, and any unusual tire wear. It is also a good idea to inspect the wheels, making sure they haven’t been bent or otherwise damaged. If you notice anything out of the ordinary, on either the tire or wheel, have it examined by a professional. Next, if the tire tread seems to be getting shallow, use a tread gauge and check the tread depth. (Tread gauges are inexpensive and available at auto-parts, RV, and tire stores.) Wear bars of smooth rubber will appear across the tread when it wears down to 2/32-inch. When wear bars appear on a tire, it means that it is no longer safe for use and needs to be replaced immediately. If your coach has a gross vehicle weight rating (GVWR) in excess of 10,000 pounds, federal requirements dictate that the tire be replaced when the tread depth reaches 4/32-inch. This means that your tires may need replacing before the wear bars show. For maximum safety and handling, replace the tires before the tread wears down this much.
As you give your tires the once-over, pay particular attention to the inside tires on dual axles, looking closely at the two facing sidewalls. A bright flashlight helps when looking between the tires. Check for all the abovementioned problems, especially bulging. Also, the two tires should be the same distance apart all the way around and should never touch, or “kiss.” Dual kissing tires build up excessive heat from friction and can experience a catastrophic failure. If you see the tires kissing, the problem may not be just improper inflation. Dual kissing can be caused by a number of factors, including underinflation, incorrect tires (size, load rating, etc.), improper mounting, improper spacing, and even casing growth. This last condition occurs when the tire cords actually stretch or expand a little, causing the tire sidewalls to bulge slightly.
If you find that you are adjusting the pressure more often on a particular tire, have it inspected by a professional. The same also holds true if you find that a tire is down 20 percent from the specified pressure. Odds are a tire that has been driven for any length of time at such an underinflated level has internal damage. It will need professional inspection to determine whether it is safe to use.
What’s the correct pressure?
Perhaps one of the reasons tire pressures aren’t checked more often is that many motorhomers just don’t know what the correct tire pressure should be for their vehicle. Many folks just see the maximum pressure rating stamped onto the sidewall and inflate the tire to that pressure, which, coincidentally, is exactly what many tire dealers do as well. Since the owners don’t know the vehicle’s GVWR and how much load is being hauled, they assume that maximum pressure is the safest setting. While running a tire at its maximum rated pressure may not hurt the tire, it can affect handling, traction, and ride quality.
The smarter way to inflate a tire is to know what the rated pressure is for the tires on your vehicle. This is determined by the vehicle manufacturer, not the tire maker. That is why two similar coaches with the same brand/size tires can be specified with different tire pressure ratings. The manufacturer determines the correct tire inflation level depending upon the GVWR, number of axles, cargo carrying capacity (CCC), and other factors. When the vehicle is built, the manufacturer is required to affix a Federal Data Plate that lists the chassis manufacturer, vehicle builder, vehicle identification number, GVWR, gross axle weight rating (GAWR), tire size, wheel size, and cold tire inflation pressure. Usually, this sticker is on the driver’s door post, but in motorhomes it can be on or near the passenger door, on the inside of the glovebox, on the inside of a closet or cabinet door, or on the inside of the fuel filler door. Your motorhome also will have a Recreation Vehicle Industry Association (RVIA) data plate inside one of the cupboard doors. This plate is voluntarily affixed by the manufacturers that belong to this association and contains additional information about the vehicle’s CCC and towing information.
The thing to remember about the Federal Data Plate is that it was affixed when the vehicle was built and the pressure listed pertains only to the tire size listed on the plate. If you or a previous owner has changed the tire brands/size, or the vehicle has been modified, or extra accessories have been installed, this data may no longer be valid. If that is the case, you’ll have to do some research to determine the correct tire pressure for your coach. Be aware that the correct pressure for the tires you run is dependent upon the weight of a fully loaded vehicle. You’ll need to weigh your motorhome to determine the current weights and compare them against the data plate. If the figures are higher than they were originally, you are overloaded in one or more categories and will need to balance your load and adjust the weight accordingly to reduce strain on the axles and wheels/tires. You’ll also need to visit RVSEF’s Web site (see sidebars) and follow the links to the tire manufacturers’ load/inflation tables, which list the weights that can be supported by various tires and air pressures.
Weighing your motorhome
Even if your vehicle is running the wheels/tires noted on the data plate and you are keeping the tires at the correct inflation levels, it is still a good idea to have your vehicle properly weighed so you can determine whether you are overloaded on one or more axles. Overloading a coach will affect virtually every aspect of performance, as well as handling, safety, and tire wear and tear. Operating an overloaded coach is not only unsafe, it is expensive, because of the extra cost involved in replacing worn components.
RVSEF has been weighing motorhomes at various RV events around North America since 1993. RVSEF officials say that of the more than 9,000 motorhomes and trailers they’ve weighed, almost 25 percent were carrying loads exceeding the load index of the tires. Knowing what your coach weighs and keeping it within federal standards is vital for your safety and the safety of others. Take your vehicle to a public scale or a truck stop and have it weighed. This is more than just a drive-on/drive-off process. Weighing a vehicle properly takes time; you’ll need to obtain the total weight (with the vehicle loaded for a trip is best), front axle weight, and rear axle(s) weight. Weighing the vehicle and axles separately is important; it is possible to be under your GVWR and still have an overloaded axle. Because you want to obtain accurate figures, it is a good idea to weigh the vehicle as it is used, with LP gas and water tanks full, fuel full, all your gear, food, and the number of passengers you usually carry. (Editor’s note: Black Cat scales, located at many truck stops throughout the United States, offer segmented scales that can weigh your coach’s axles separately yet simultaneously.)
To keep maneuvering to a minimum, drive forward just until the front wheels are on the scale and get weighed. Then pull the entire vehicle onto the scale and have it weighed. Finally, pull forward so just the rear axle(s) are on the scale and get weighed again. Compare these figures against the data plate and adjust your load and tire pressures accordingly. For overloaded axles, the fix may be as simple as rearranging your load and adding a few pounds of pressure to a couple of tires. However, if you find that your gross combination weight rating (GCWR “” the weight of your loaded motorhome and its towed vehicle or trailer) exceeds the data plate’s GCWR, you are exceeding the design parameters of the vehicle. This is a potentially dangerous condition that needs to be corrected immediately. Hauling more weight than the vehicle is designed to pull puts extra stress on the engine, transmission, chassis, drivetrain, brakes, suspension, and tires, and it means your coach is an accident waiting to happen.
It is also good to weigh individual wheel positions and the left and right sides of the vehicle. This takes a little extra time and is not always easily done, because there must be enough room around the scale to accommodate half the vehicle being off the side of the scale. The fact that many scales are crowned for rain runoff makes accurately weighing the left and right halves of the vehicle difficult, as the crowned surface of the scale throws some of the vehicle weight to one side. The ideal way to obtain individual wheel weights is to take advantage of the RVSEF motorhome weighing program at an FMCA convention or area rally. RVSEF safety team members use sophisticated portable scales to weigh the coach wheel by wheel.
Age and storage
Although the tires on your coach probably are designed for an expected life of between 60,000 and 80,000 miles, most motorhome tires need replacing long before this figure is reached. The average motorhome is driven only 5,000 to 6,000 miles a year and spends much of its life being parked. Driving this annual distance means that to get 80,000 miles on a set of tires would take more than 13 years of consistently perfect tire care. While this is theoretically possible, in real life it is virtually impossible because of the way tires are used and abused, and the way they age. Driving habits, improper inflation levels, carried load, road conditions, component wear, driving speed, and environmental damage contribute to tire wear and aging.
Storing your coach for months at a time is not good for long-term tire life, because stored vehicles usually experience prolonged underinflation of the tires, which overloads them. In addition, tires are intended to roll while carrying a load, and manufacturers have engineered their tires with compounds in the rubber that are released as the tires heat up from use. These compounds keep the rubber flexible, and some of them have antiozone properties that protect the rubber from sun damage. When the motorhome is parked for prolonged periods, there is no heat buildup within the rubber to release these compounds, so the tire dries out and becomes more brittle. Because of all these factors, industry experts agree that the average life for an RV tire is about six years from the date of manufacture before replacement becomes necessary. (For help in determining the age of your tires, see the accompanying article titled “Deciphering Tire Markings.”)
Because the nature of motorhoming makes it difficult to guarantee that you will always park on a level surface, leveling the coach by parking one or more wheels on boards or blocks is usually necessary (if your coach is not equipped with levelers). The problem with blocking tires (especially radials) to level the coach is that unless it is done properly it can put undue strain on the steel cables in the tire, causing severe strain and premature fatigue of the sidewalls. To assure maximum support and even load distribution, tire blocks should always be wider and longer than the tire footprint.
Unless you are a full-timer, your motorhome will spend a significant part of its life in storage, and as I have already explained, this is not good for the long-term life of the tires. If you find you have to park your coach for longer than 30 days, it is a good idea to protect the tires as much as possible from overloading, flat spotting, and drying out. The best way to do this is to park your vehicle inside. However, most of us have to leave our coaches parked outside in a driveway or storage lot. Some parking surfaces may cause your tires to age more rapidly than others, so it is always a good idea to place a barrier between the tire and the parking surface. You can use cardboard, plywood, or a plastic tarp for this purpose. I recommend laying a large plastic tarp down over the whole parking surface, if possible, before storing the motorhome.
It is also a good idea to scrub the tires with a mild detergent solution and a stiff brush beforehand to remove acids, chemicals, and tire-damaging dirt. I don’t recommend using tire dressings, because these can effectively seal the tire surface and stop the rubber from breathing. Because tires tend to lose air through permeation, it is also wise to inflate all the tires (including the spare) to 10 percent above the maximum recommended pressure stamped on the tire sidewall to prevent overloading them as they lose air. If you plan to store the vehicle for a prolonged period, the best thing to do is to put the axles on blocks to take the strain off the tires. Don’t ever block the vehicle frame or use the levelers, because this could cause the suspension to sag over time. Don’t forget to shield the tires from the sun’s damaging effects by shading them with a protective covering. Remember to check the air pressure and adjust inflation levels before putting the vehicle back into service.
If you decide to remove the tires from the vehicle and store them separately, make sure it is a clean, dry, and cool area that is out of the weather and out of direct sunlight. Before stacking the tires, put a protective layer on the storage surface, and position the tires so that the bottom tire retains its shape. Inflate the tires to 10 percent above the maximum inflation pressure stamped on the sidewall.
Taking the time to properly care for your motorhome tires will reap benefits in many ways, not the least of which is helping to ensure your family’s safety while traveling.
These three international tire giants have a long history in the tire business and in serving the RV community.
Goodyear Tire & Rubber Co.
1144 E. Market St.
Akron, OH 44316-0001
Named after Charles Goodyear, the man who invented vulcanizing, the Goodyear Tire & Rubber Co. was founded in 1898 by Frank Seiberling and has been the world’s largest tire company since 1916. Goodyear offers several tires for motorhome applications. The most notable is the G670 RV.
- G670 RV Unisteel “” Available in both 19.5 and 22.5 sizes, the G670 RV was designed for motorhome applications. According to the company, the G670 RV Unisteel offers an improved ride, increased fuel economy, and less noise and vibration than truck tires. In addition to a cool-running rubber compound, the G670 RV is constructed with anti-ozone/UV compounds that help to protect the whole tire from the damaging effects of ozone and ultraviolet light.
- G149 RSA “” This all-position radial tire features straight tread ribs and a flat tread radius for even wear. Suitable for type A and C motorhomes.
- G169 RSA “” This all-position radial tire features straight tread ribs and a flat tread radius for even wear. Suitable for type A motorhomes.
P.O. Box 19001
Greenville, SC 29602
The French tire giant has roots that go back as far as 1829, with the current company being established in 1889 by Andre and Edouard Michelin. It has been manufacturing tires since 1908 and designed the first radial truck tire in 1952. Its history in the United States dates back to 1907 when the company set up its first stateside manufacturing facility. The company currently offers at least five radial tire lines suited for motorhome use:
- XRV “” An all-wheel, all-position radial with a cool-running five-rib tread design that features large rain grooves for improved wet-weather traction and handling. In addition, this model features built-in antiozone protection in the sidewalls.
- XZ2/XZA2 “” These ultra-fuel-efficient tires feature a five-rib/four-groove design with low rolling resistance for improved fuel economy and enhanced traction. The XZA2 is designed for steering axles and features variable groove angles and miniature siping in the tread for improved handling.
- XZA “” This five-rib design features large shoulders to reduce scrub/vibrations and extend tire life. Zigzag groove angles make this tire good for all-position usage.
- XZ1 “” An even-wearing radial with a flat crown radius to enhance wear and retreadability. Miniature sipes and variable zigzag grooving make this tire good for steering axles.
- XZE “” This all-wheel radial features an extra-wide and deep tread design for enhanced scrub resistance. Buttressed shoulders and extra-strong curb guards protect sidewalls from curb hits and stone drills.
6261 Katella Ave., #2B
Cypress, CA 90630
This well-known Japanese tire giant was established just after the end of World War II and starting exporting truck tires in 1947. The company has had a U.S. office since 1966 and starting in 2006 will be manufacturing tires in the United States. The company offers six tire lines suitable for type A motorhome use:
- M120Z “” Designed for an all-wheel, all-position installation, it has exceptional durability and even wearing properties.
- M124Z “” This five-rib/four-groove radial has a deep 19/32-inch tread design for long-wearing, over-the-highway driving.
- M147 “” Intended for over-the-road axles and trailering applications. Main features are superior highway traction, long-lived casings, and a side groove design that helps to enhance fuel economy.
- M111Z “” Features four zigzag ribs with wide grooves for steering stability and a high tread volume for long-wearing ability.
- M143 “” Designed with durability in mind for local delivery service and RV applications.
- M54 “” This all-position summer tread has wide grooves for excellent wet-weather traction and solid outer shoulders to reduce transmitted noise.
Tire Information Sources
In addition to the tire information available from the tire manufacturers listed in this article, the following resources may be of some value:
RV Safety Education Foundation Inc. (RVSEF)
4575 Annette Court
Merritt Island, FL 32953
The RVSEF Web site has links to tire company load/inflation tables. The organization also offers a comprehensive safety education program for RVers that covers personal safety, tires, towing, loading, handling LP gas, fires, etc.
Rubber Manufacturers Association (RMA)
1400 K St. N.W.
Washington, D.C. 20005
The RMA Web site has tire safety information, motorhome tire FAQs, seasonal driving tips, and how-to information.
This tire-industry-supported educational Web site provides a host of general information about tires and tire care.
Terms You Should Know
GAW “” Gross axle weight is the weight of a fully loaded vehicle that is carried by a single axle.
GAWR “” Gross axle weight rating is the maximum weight rating the components (axle, brakes, springs, wheels/rims) of each axle are designed to support.
GVW “” Gross vehicle weight is the weight of a fully loaded vehicle including vehicle, cargo, passengers, liquids, fuel, food, towed vehicle’s tongue weight, and so on. The GVW must be less than the GVWR.
GVWR “” Gross vehicle weight rating is the maximum weight (as established by the manufacturer) the chassis can safely support and includes the weight of the vehicle, cargo, passengers, food, fuel, liquids, and so on.
GCWR “” Gross combination weight rating is the maximum allowable total loaded weight rating of the vehicle and any trailer or vehicle it is towing. Subtracting the GVWR from the GCWR will give you the allowable weight for any towed trailer or vehicle.
SCWR “” Sleeping weight capacity is calculated by multiplying the number of sleeping positions (as defined by the manufacturer) times 154 pounds, the “average” weight of a person. If your passengers weigh more than an average of 154 pounds each, you’ll need to reduce the number of people sleeping in the motorhome.
CCC “” Cargo carrying capacity is the GVWR minus the UVW and without any water or LP gas in the respective tanks, and subtracting any dealer-installed accessories, the SCWR, and any tongue weight.
UVW “” Unloaded vehicle weight is the weight of the vehicle with full fuel tanks and minus cargo, water, LP gas, dealer-installed accessories, or passengers.
Tongue weight “” The downward force that is exerted on a hitch by a fully loaded towed vehicle or trailer.