Useful Info - Tyres

The Importance of Air Pressure

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

A tyre that is under inflated 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 tyre failure. A tyre that is under inflated will also cause poor vehicle handling, rapid and/or irregular tyre wear, and a decrease in its fuel economy.

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

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

What pressure should I have in My tyres?
The law requires that the tyres maximum load rating be moulded into the sidewall of the tyre. On the tyres sidewall you can see the maximum load allowed for the size tyre 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 tyre.

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 tyre must never exceed the maximum inflation rating stamped on it.

When Should I Check my RV's Tyre Air Pressure?
You should check the air pressure every two weeks or at least one a month and before any major trip. Your RV tyres air pressure should be checked every "drive" morning on long trips. On short trips of a day or less driving each way, your tyres 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 tyres 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 tyres 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 tyre.

It is recommended you purchase a quality truck tyre 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 tyres 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 tyre 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 tyre. 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 tyre next to the low air pressure tyre is going to heat up from carrying double its load, which will cause both tyres to fail. Then you'll have two tyres 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 tyres, 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 tyre 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.
Where to Weigh Your Vehicle.

You will need to find a public weighbridge in your local area. There will be a nominal fee to pay to weigh your vehicle, which is money well spent, following which you will be issued with a weigh ticket. This will indicate the weights of the front axle, gross vehicle weight and the rear axle.

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 various types of weighbridge available.
Guidance can be sought from the operator at the weighbridge on how to weigh your vehicle in order to obtain the weights of the front axle, gross vehicle weight and rear axle. You may well be surprised at just how much weight you are really carrying!

Common Tyre Damage and Tyre Wear

No tyre, regardless of its quality, is indestructible. Certain conditions of use and abuse can stress a tyre beyond reasonable operating limits, causing it to come out of service even when considerable tread remains. Such conditions are clearly indicated by the damage they leave on the tyre itself. Below are listed common types of damage 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 tyre. Overload and/or under inflation for a given load, and improper blocking of the tyres 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 tyres in dual configuration make contact while in operation. The heat generated by the friction between the two tyres severely weakens the casing material of the dual tyres. This is easily seen on the sidewalls of the tyres where the duals come in contact. The condition may be caused by several factors:

  • improper mounting
  • incorrect dual spacing
  • under inflation
  • "casing growth"

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

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

In extreme cases, the sidewall of the tyre is destroyed, from the excessive heat it endured, due to the weight of the vehicle pressing on the tyre 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 under inflated sidewall. According to guidelines put out by the Rubber Manufacturers Association, any tyre 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 tyre in a dual configuration comes out of service due to under inflation/run flat damage, the other tyre in the dual configuration should be inspected immediately. If the unserviceable tyre was under inflated, that means the serviceable tyre was carrying more and more of the load for that wheel position. Consequently, it too may have suffered some casing damage.

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

Toe Wear
A feathered wear pattern on the front tyres typically indicates misalignment (toe in or out). Sometimes a radial tyre will not have this wear pattern unless the toe condition is severe. Instead of the feathered edge wear, the tyre 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 tyre and feathered edge on the opposite shoulder of the other front tyre. In order to correctly diagnose a tyre 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 tyres may be due to negative camber or toe-out, a misalignment. If only one tyre shows edge wear, check for worn kingpin bushings, bent or worn steering components, or excessive positive camber setting.

Rotation/Cleaning/Tyre Life

Tyre Rotation
If correct air pressure and proper alignment are both continually maintained, tyre rotation may never be needed. However, in other cases, tyre rotations may be needed to help even out alignment, under inflation, or free rolling wear problems. Follow your motorhome manufacturer's rotations service recommendations. ALWAYS ensure that your wheel nuts are correctly torqued up after replacement.

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

As with the cleaning of any rubber product, proper care and methods in cleaning must be used to obtain the maximum service years out of your tyres. 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 tyres from ageing, use extra care and caution. tyre 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 tyre. Heat can add to the negative reaction. When these same dressing products are used on a passenger car tyre that is replaced every three to four years, it is rare to see a major problem. However, in most cases, RV tyres may last much longer due to limited annual mileage, and the chemical reactions have much longer to take effect.

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

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

Tyre Inspection
Your RV tyres should be inspected thoroughly at least one 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 inside sidewalls, the tread area, and the valves, caps, and any valve extensions. Inspect for nails, cuts, bulges, ageing, or fatigue cracks and weathering or ozone cracking. Also, check between the duals for objects lodged between them.

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

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

To protect your tyres from these common damage conditions:

  • Keep tyres properly inflated
  • Keep tyres clean
  • Avoid prolonged exposure to heat, cold or moisture
  • Cover your tyres when vehicle is not in use
  • Do not park near electric generators or transformers
  • Do not store vehicles in an area where welding is being done or in a garage which has mercury vapor lamps

On a regular basis, rub the palm of your hand across the face of the tread on your front tyres 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 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 tyres in just a few hundred miles.

Long-Term Storage/Selecting Replacement Tyres

Your RV is designed for recreation, not long-term storage. However, unless you are a "full timer", you have no other choice. Rubber tyres 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 tyres to age prematurely. For this reason, it is recommended that you place a barrier (i.e. card board, plastic, or plywood) between the tyre and the storage floor/ground surface.

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

Before removing your vehicle from long-term storage, thoroughly inspect each of its tyres. This means a close examination of each tyres tread area, and air pressure. If your pressure check indicates the tyres 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 Tyres

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

The 'Blocking' Methods

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

Selecting Replacement Tyres for Your RV
One of the most important RV equipment purchases that you will make will be the replacement tyres on your RV. If you obtained good service with your first set of tyres, 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.