How to Get the Most from Your Recreational Vehicle Tires brought to you by Michelin North America

For more information on the Michelin dealer nearest you, check your local telephone directory or call 1-800-847-3435.

This article posted on December 6, 2004


Topics Covered:

The Importance of Air Pressure

How to Determine Your RV's Correct Weight

Common Tire Damages and Tire Wear

Rotation/Cleaning/Tire Life

Long-Term Storage/Selecting Replacement Tires

The Importance of Air Pressure

The most important factor in maximizing the life of your tires is maintaining proper inflation. Driving on any tire that does not have the correct inflation pressure for the load of the vehicle is dangerous and may cause premature wear, tire damage, and/or loss of control of the vehicle.

A tire that is underinflated will build up excessive heat that may go beyond the prescribed limits of endurance of the rubber and the radial cords. This could result in sudden tire failure. A tire that is underinflated will also cause poor vehicle handling, rapid and/or irregular tire wear, and a decrease in its fuel economy.

Overinflation will reduce the tire's footprint or contact patch with the road, thus reducing the traction, braking capacity, and handling of the vehicle. A tire that is overinflated for the load that it is carrying will also contribute to a harsh ride, uneven tire wear, and will be susceptible to impact damage.

Maintaining correct tire inflation pressure for each loaded wheel position on your vehicle is of the utmost importance and must be a part of regular vehicle maintenance.

How Much Air Should I Carry in My Tires?

Federal law requires that the tire's maximum load rating be molded into the sidewall of the tire. On the tire's sidewall you can see the maximum load allowed for the size tire and load rating, and the minimum cold air inflation pressure needed to carry that stated maximum load. Utilizing less air pressure means a lesser load can be carried by the tire.

The amount of air pressure you need to use is dependent on the weight of your fully loaded vehicle.

It is important to note that the cold inflation pressure for the tire must never exceed the maximum inflation rating stamped on the wheel.

When Should I Check my RV's Tires' Air Pressure?

You should check the air pressure every two weeks or at least one a month and before any major trip. Your RV tires' air pressure should be checked every "drive" morning on long trips. On short trips of a day or less driving each way, your tires should be checked before you leave on your trip and again before you start your trip home. If your vehicle is stored for any length of time, air pressure should be checked prior to storage, but more importantly, when it comes out of storage.

Check your tires when they are "cold" and have not been driven for more than one mile. The stated load capacity for a given cold inflation pressure is based on ambient outside temperature. If you must check your tires when they are warm or hot, do allow for a slight increase in air pressure and make sure they are within a couple of pounds of each other on the same axle. Never let air out of a hot tire.

It is recommended you purchase a quality truck tire air gauge which has an angled dual head. This type of gauge allows you to check inflations on the inner dual wheel which has the valve stem pointing toward you, and on the outer wheel which has the valve stem pointing away from you. Nothing should restrict your ability to check a tire's air pressure daily when you are driving your RV. Pressure sealing valve caps should always be used to prevent air from escaping from the valve stem. If you use valve stem extension hoses, make sure they are good quality stainless steel braid reinforced and are securely anchored to the outer wheel. If your RV has wheel covers which must be removed to check the inflation, then consider removing them on a long trip, as the extra time and effort required may lead you to avoid checking your air pressure.

What if You Don't Check Your Air Pressure?

If a tire picks up a nail or screw that creates a slow leak and causes some air pressure loss, you might eventually spot it visually if it's a front tire. If it is an outside rear dual, you might also spot it with a visual inspection. However, if it is an inside rear dual, the chances of spotting it without an air pressure check are very slim. If you begin driving without finding it, very quickly (in most cases a few miles) your outside rear tire next to the low air pressure tire is going to heat up from carrying double its load, which will cause both tires to fail. Then you'll have two tires down on the same side and on the same axle, and a five ton or more vehicle at any speed is difficult to bring under control.

How to Determine Your RV's Correct Weight

The GVWR (Gross Vehicle Weight Rating) and GAWR (Gross Axle Weight Rating) stickers on your motorhome (normally located on the support pillar next to the driver's seat) will show you the chassis manufacturer's and/or the motorhome manufacturer's total vehicle maximum weight ratings and per axle weight rating.

The GVWR is the maximum total weight for which the vehicle is rated - including passengers, fluids, and cargo. The GAWR is the maximum for which a single axle is designed. These per axle and total maximum weight ratings could be limited by the tires, wheels, axle and axle bearings, springs, the vehicle frame, or other components of the vehicle.

The GAWR sticker is only a guide in knowing your maximum loaded axle weights and subsequently your correct tire inflation pressure. Every motorhome, even of the same make and model, will vary in actual loaded axle weights, because of different options and personal loads.

While your actual, loaded axle weight should be below the GAWR, you must weigh your motorhome in a loaded condition to know its actual weight. Weigh the front axle, the total unit, and then the rear axle. It is possible for a vehicle to be within the GVWR yet overloaded on an axle. It is even possible for one wheel position to be overloaded, even though the GAWR has not been exceeded. For this reason (if there is room to the sides of the scale) Michelin recommends weighing each wheel position of the vehicle. This will give you a clear indication of exactly how the weight of your motorhome is distributed. The Tire Industry Safety Council publishes a "Recreational Vehicle Tire Care and Safety Guide" which includes instructions on how to weigh your vehicle by wheel position.

Links to selected instructions and diagrams are presented here: Weighing Your Single Axle Recreational Vehicle or Weighing Your Tandem Axle Recreational Vehicle. Print the correct diagram/instruction from the links for your type of RV and use in conjunction with the "How to Weigh Your RV" section found below.

Where to Weigh Your Vehicle

There are probably several certified public scales in your area. You will find public-access scales in a variety of places, such as moving and storage company lots, farm suppliers with grain elevators, gravel pits, recycling companies, and large commercial truck stops.

If you are not aware of a nearby public scale, check your phone book's yellow pages under "scales-public" section or "weighers". A nominal fee will be charged, but this is money wisely spent.

How to Weigh Your RV

Your RV must be weighed fully loaded, that is, with passengers, food, clothing, fuel, water, propane, supplies, etc. Any towed vehicle (car/pickup, boat or trailer) or item loaded on brackets on the back of the RV, such as bikes or motorcycles, should also be included in the weighing.

There are three types of scales: 1. Platform. 2. Segmented Platform. 3. Single Axle.

1. The platform scale is long enough to weight the complete vehicle.

2. The segmented platform scales can provide individual axle weights and total vehicle weights simultaneously, when the vehicle is positioned properly.

3. Single axle scales weigh one axle at a time.

1) The platform scale is long enough to weight the complete vehicle. The following steps are suggested and are illustrated with diagrams found in the above links under "How to Determine Your RV's Correct Weight".

a) Pull onto the scale so that only the front axle is on the platform (with the end of the scale midway between the front and rear axles), and record the scaled weight.

b) Pull forward until the full unit is on the scale, and record the scaled weight.

c) Pull forward so that only the rear axle is on the scale (again with the edge of the scale midway between the front and rear axles), and record the scaled weight.

d) If the RV has a rear tag axle, pull forward so that only the tag axle remains on the scale, and record the scaled weight.

If there is no towed vehicle, this weight will represent the actual weight on the tag axle. To determine the actual load on the rear axle, subtract this value from the recorded weight in step 1c. If there is a towed vehicle, proceed to step 1e (see link above for "Weighing Your Tandem Axle Recreational Vehicle"), to obtain the "towed vehicle only" weight. Subtract that value from the value above and then subtract that from the weight recorded in step 1c.

If a boat, trailer or other vehicle is being towed, it should be weighed and combined with the towing vehicle's GVW (Gross Vehicle Weight) to ensure the total weight does not exceed the GCWR (Gross Combined Weight Rating).

2) The segmented platform scales can provide individual axle weights and total vehicle weights simultaneously, when the vehicle is positioned properly.

Position the vehicle on the scales so that each axle is centered as much as possible on separate segments, and record the weight. Reposition the vehicle so that only one side is on the scale, again centered on the segment as much as possible. Subtract the weighed wheel positions from the total axle weights to determine the unweighed wheel positions' weights.

3) The single axle scale weighs one axle at a time.

Drive your front axle onto the scale and stop long enough for the weight to be recorded. Pull vehicle forward until the rear axle is on the scale. To obtain the gross vehicle weight add the two axle loads together. To obtain the individual wheel position weights, repeat this process with only one side of the RV on the scale.

Note: Even though the weight of the total axle may be within the axle's rating, it may be overloaded on one side. This causes one wheel position to be overloaded. Therefore, side-to-side weighing should also be done.

Your RV must remain as level as possible on the scale (even though an axle or side is not physically on the scale). Obviously, to obtain the side-to-side weights, there must be enough space on either side of the scale to accommodate the RV being partially off the scale.

If there is a difference in the weights on one side of the vehicle as compared to weights on the other side, components (tires, wheels, brakes, springs, etc.) on the heavier side could be overloaded, even though the total axle load is within the GAWR. It is important to redistribute the load to avoid component failure, as well as to improve the handling characteristics of the vehicle. With these actual weights, it is now possible to compare them against the GAWR, GVWR and tire capacities. These weights are also what should be used to help determine the proper air pressure for the tires.

If you are towing a vehicle or trailer, you need to know your RV's GCWR (Gross Combined Weight Ratings). This is the total actual loaded weight of your RV (or tow vehicle) plus total actual loaded weight of the towed vehicle (or trailer). The total actual loaded weight of the RV and towed vehicle should not exceed the GCWR. While the GCWR has more to do with the drivetrain (engine, transmission, axle, brakes, and bearings) design limits, this additional weight can also affect the tires and how your RV (or tow vehicle) handles. And finally, please don't forget to consider the tongue weight of the trailer.

Common Tire Damages and Tire Wear

No tire, regarless of its quality, is indestructible. Certain conditions of use and abuse can stress a tire beyond reasonable operating limits, causing it to come out of service even when considerable tread reamins. Such conditions are clearly indicated by the damage they leave on the tire itself. Below are listed common damages and the signs they leave behind. Please understand that this list is by no means exhaustive and is intended only as a general guide.

Fatigue Rupture

This type of damage is sometimes called a "zipper rip" because of the zipper-like effect it creates in the steel casing cords of the damaged tire. Overload and/or underinflation for a given load, and improper blocking of the tires can cause the steel casing to fatigue and result in this type of damage. As one cord breaks, each cord around it is subjected to even more stress. Eventually the weakened cords may break, one after the other, until a rupture occurs in the upper sidewall.

Dual Kissing

This type of damage refers to what happens when two tires in dual configuraton make contact while in operation. The heat generated by the friction between the two tires severely weakens the casing material of the dual ties. This is easily seen on the sidewalls of the tires where the duals come in contact. The condition may be caused by several factors:

In this last case, the fabric casing cords of the tire actually stretch and expand, causing the tire to touch or kiss, under load at the contact patch.

Underinflation

This condition is often referred as a "run flat" tire. It is caused by operating a tire at very low or zero air pressure. When a tire is run at normal highway speeds, underinflated, it flexes too much and builds up heat. This heat damages the inner liner, casing and outer sidewall of the tire. If not remedied quickly, the tire will be irreparably damaged.

In extreme cases, the sidewall of the tire is destroyed, from the excessive heat it endured, due to the weight of the vehicle pressing on the tire casing without the cushioning effect of the correct air pressure, and due to the crushing/cutting action of the wheel as it rolls on the uninflated sidewall. According to guidelines put out by the Rubber Manufacturers Association, any tire that has been run at less than 80% of recommended air pressure for the load it is carrying should be inspected for possible damage.

When one tire in a dual configuration comes out of service due to underinflation/run flat damage, the other tire in the dual configuration should be inspected immediately. If the unserviceable tire was underinflated, that means the serviceable tire was carrying more and more of the load for that wheel position. Consequently, it too may have suffered some casing damage.

Tire Wear

All tires mounted on RV's should wear in a smooth, even wear pattern when the tires are maintained with the correct air pressure for the load on the tire. If tires begin to show an irregular wear pattern, and the vehicle alignment is correct, sometimes just rotating the tires by changing direction of rotation and wheel position will allow the tires to wear evenly.

Toe Wear

A feathered wear pattern on the front tires typically indicates misalignment (toe in or out). Sometimes a radial tire will not have this wear pattern unless the toe condition is severe. Instead of the feathered edge wear, the tire will be worn on the inside or outside shoulder which could be confused with camber wear. A skewed rear axle could show feathered edge wear on one shoulder of one front tire and feathered edge on the opposite shoulder of the other front tire. In order to correctly diagnose a tire wear condition, the motorhome should have the alignment checked on all four wheel positions before any corrections to alignment are made.

Camber Wear

Also known as edge wear, camber wear shows up on the inside or outside shoulders of the tread. Wear on the inside edge of both tires may be due to negative camber or toe-out, a misalignment. If only one tire shows edge wear, check for worn kingpin bushings, bent or worn steering components, or excessive positive camber setting.

Rotation/Cleaning/Tire Life

Tire Rotation

If correct air pressure and proper alignment are both continually maintained, tire rotation may never be needed. However, in other cases, tire rotations may be needed to help even out alignment, underinflation, or free rolling wear problems. Follow your motorhome manufacturer's rotations service recommendations.

Proper Cleaning

Road oil will cause deterioration of the rubber and dirt buildup will help hold the chemicals in the air next to the tire and will also deteriorate the tire.

As with the cleaning of any rubber product, proper care and methods in cleaning must be used to obtain the maximum service yeras out of your tires. A soft brush and the normal mild soap that you would use to clean your RV may be used. If you use a dressing product to "protect" your tires from aging, use extra care and caution. Tire dressings that contain petroleum products or alcohol may cause deterioration or cracking.

In many cases, it is not the dressing itself that can be a problem, but more the chemical reaction that the product can have with the antioxidant compound in the tire. Heat can add to the negative reaction. When these same dressing products are used on a passenger car tire that is replaced every three to four years, it is rare to see a major problem. However, in most cases, RV tires may last much longer due to limited annual mileage, and the chemical reactions have much longer to take effect.

Tire Life

The life of a tire used on an RV cannot be measured by miles alone. Your RV tire life depends on driving habits, driving conditions, and geography, as well as the age of your tires.

Just like your fan belt and radiator hoses, the rubber in your tires ages as well. In cooler, clean air locations, the expected tire life will be longer than in high temperature, high ozone areas. Of course, as a tire ages, you should inspect it more frequently.

Tire Inspection

Your RV tires should be inspected thoroughly at least once a year, and any time you drive in rough or rocky terrain, or when you have your RV serviced.

This inspection should include both the outside and insdie sidewalls, the tread area, and the valves, caps, and any valve extensions. Inspect for nails, cuts, bulges, aging, or fatique cracks and weathering or ozone cracking. Also, check between the duals for objects lodged between them.

During the yearly or pre-trip inspection the tires should be inspected for signs of aging, eather checking and/or ozone cracking. Look for tiny cracks in the rubber surface on the sidwall of the tires. Most often the cracks are 360 degrees around the tire.

If the cracks are less than 1/32" deep, the tires is O.K. to run. Between 1/32" and 2/32", the tire is suspect and should be examined by your tire dealer. If the cracks are over 2/32", the tire should be replaced immediately.

To protect your tires frome these common damage conditions:

On a regular basis, rub the palm of your hand acroos the facr of the tread on your front tires to feel for any feathered wear from "toe" alignment problems. (Be careful since severe wear can expose steel belt edges that are very sharp). A "toe" misalignment problem can be caused by impact with a "chuck" hole in the road. Bad "toe" wear can be hard to find visually, but can be felt very quickly with the hand. This type of alignment problem can wear rubber off the tread of your tires in just a few hundred miles.

Long-Term Storage/Selecting Replacement Tires

Your RV is designed for recreation, not long-term storage. However, unless you are a "full timer", you have no other choice. Rubber tires age faster when not being used. A cool, dry, sealed garage is your best bet for storage. However, many RVs are stored outside in the elements. Some storage surfaces may cause tires to age prematurely. For this reason, Michelin recommends placing a barrier (i.e. card board, plastic, or plywood) between the tire and the storage floor/ground surface.

There are a few steps that you can take to reduce the aging effects from long-term RV storage. Before putting your RV into storage or a non-use period, thoroughly clean your tires. Then cover the tires to block direct sunlight and ultraviolet rays. Store your RV out of a high ozone area. NOTE: When vehicle is stored, tires should be inflated to maximum inflation pressure as indicated on the sidewall of the tire.

Before removing your vehicle from long-term storage, thoroughly inspect each of its tires. This means a close examination of each tire's tread area, and air pressure. If your pressure check indicates the tires have lost air during storage, be sure to inflate them to the correct pressure for the current load before putting the unit into service.

The Use of Blocks to Level Motor Homes/RV's Equipped with Radial Tires

Extreme caution must e taken to ensure that the tires are fully supported when using blocks to level motor homes and/or RV's. The load on the tires should evenly distributed on the block and in the case of duals, evenly distributed on blocks for both tires. If not properly done, the steel cables in the sidewall of the tires may be damaged and could lead to premature fatigue of the sidewall.

The correct and incorrect methods are shown here. Please note that blocks should be wider than the tread and longer than the tire's footprint. This provides maximum support to the tires and assures that the load is evenly distributed throughout the tire's footprint area.

Selecting Replacement Tires for Your RV

One of the most important RV equipment purchases that you will make will be the replacement tires on your RV. If you obrained good service with your first set of tires, chances are that they were matched well for your RV's weight needs and your type and area of driving. You will be sure only if you have weighed your loaded RV.

If there is reason to replace your tires with another size, be very careful with this selection. There are some basic areas of concern, such as the load rating of the new tire and the overall diameter of the new tire for vehicle clearance and speedometer reading.

Then there is the matching of the tires to the dual wheel offset for the dual spacing clearance and the load rating of the wheel. For example: buying a tire with a higher load rating that might equire 105 P.S.I. would be of no advantage if your wheel is limited to 80 P.S.I. (And be sure that the wheel width is compatible with the new tire size). Consult your vehicle manufacturer for wheel specifications.


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