Your Camper's Tires, Ralph P. Yates

Camper Breakdown! A dreaded event, but one that happens all too often. What causes a breakdown? More often than not, it’s a tire failure. This should come as no surprise, as a trailer tire takes a beating, spinning at 75,000 revolutions per hour, enduring blistering hot pavement and carrying the weight of all those essentials we’ve loaded into the camper. Top that off with neglect and lack of understanding, and problems are bound to occur.

About tires: There are very real differences between auto tires and trailer tires. First, auto tires must maintain traction during all road and driving maneuvers, cornering, braking, etc., so they must have flexible sidewalls to maintain traction. Trailer tires need no traction except when the trailer brakes are applied, so they are built for high speed durability and bruise resistance under heavy loads. They are usually bias-ply instead of radial construction. When automotive tires are used on trailers, they can increase sway because of the sidewall flexibility. Another difference is that automotive tires are built to provide a comfortable ride, whereas special trailer tires (ST) are built for durability. Finally, most RVs are out of service for long periods of time, and when they are used, they’re carrying heavy loads during very hot weather.

About that Sidewall: How old is the tire? On the sidewall you’ll find the word “DOT” followed by an alphanumeric code. The last three digits of this code tell the age. For example, if it says “DOT M20127,” the last three digits reveal that the tire was manufactured in the 12th week of 1997. Of course, this doesn't indicate the decade, so you have to use a bit of judgement here.

Depending on the tire, you will find some or all of the following information on the sidewall:

• CONSTRUCTION TYPE _ Bias Ply vs. Radial
• APPLICATION TYPE _ (ST) Special Trailer, (P) Passenger Car, (LT) Light Truck
• SIZE _ This can be shown in several ways:
• The Numeric System _ Sizes such as 4.80 X 8 are found on smaller trailer tires. This indicates the tire section width (4.80"), and the rim diameter (8"). Section width is the width of the tire at its widest point;
• The Alpha Numeric System _ This is common on 13 to15 inch trailer tires. Size B78 X 13C indicates air chamber size (B), the 'Aspect Ratio' (78), the rim diameter (13"), and the load range (C). The Aspect Ratio is determined by dividing the height of a cross-section of the tire by the section width;
• The Metric System _ This is becoming very common. Size ST205 75D 15 indicates the tire application type (ST_special trailer), the section width (205mm), the 'Aspect Ratio' (75), the construction type (D= bias ply), and rim diameter (15");
• LOAD RANGE - The carrying capacity. This is now stated as Load Range B, C or D, which correspond respectively with the old standard, 4, 6 and 8 ply;
  RIM SIZE _ Diameter and width must match the tire ;
• MAXIMUM PERMISSIBLE INFLATION PRESSURE - more on this below.
• Certification Label: – Recreational vehicles manufactured since 1972 come with a certification label which provides the following information relating to tires and loads:
  • Gross Vehicle Weight Rating (GVWR)
  • Gross Axle Weight Ratings (GAWR) for each axle
  • Tire and rim sizes
  • Recommended cold tire inflation pressures
    This label can be found on several different locations within your vehicle, but if you can’t find it, look in the owner’s manual. The manual also contains information about alternate tire sizes. If you are considering changing to a tire size other than those shown on the certification label, be sure to consult with your vehicle manufacturer, tire dealer or tire manufacturer. Using the wrong size tire can lead to tire failure.

Selection of replacement tires: Trailer tires are available as tire alone or in tire-rim sets. If your current rims are rusted, go for the sets. It is important to match the new rim to the old as regards the number of bolt holes and their pattern. Be sure the 'bolt circle' pattern is the same as the axle hub. The bolt circle is described by two numbers, such as 5 x 5.5. The first number is the number of holes and the second is the diameter in inches of an imaginary circle passing through the center of each hole.

When replacing your trailer tires/rims it is critical that the proper size and load range be selected in order to match the load requirements of the trailer. Make sure your tires say ST on them, not P for passenger or LT for light truck. If you do buy a higher rated tire don't automatically assume you can pack more stuff in your camper. The tires are only one part of the system which determines the capacity of the trailer.

Tire maintenance: Rubber naturally oxidizes over time and can result in cracking of the tire. Scrubbing four times a year with mild detergent will remove the oxidation. Avoid harsher cleaners and degreasers, as they can dry out the rubber. You will find that a nylon scrub brush does an excellent job cleaning tires.
Your tire’s sidewall contains a statement such as, “Capacity 1200 lbs. at 50 p.s.i.” Keep that tire inflated to 50 psi and check it only when the tires are cold. Resist the temptation to bleed off excess air when the tires get hot, as this increased pressure due to heat has been taken into consideration. Measure tire pressure with a tire gauge, not by how the tire looks. A tire can lose half its pressure and still not appear flat.

Underinflation causes excessive tire wear, premature failure and excessive sway. It also causes tires to flex more than they should, which causes increased friction and heat buildup. An overinflated tire will wear in the center, while those underinflated will show more wear at the edges. While you’re checking your tires, be sure to check your lug nuts for tightness. It’s a good idea to do this every day you’re on the road.

Inspect tires for uneven wear patterns, cracks, foreign objects, or other signs of wear or trauma. Remove bits of glass and other foreign objects wedged in the tread. If you see a scallop-like pattern around the edges (also called cupping) you may have a loose wheel bearing or possibly an alignment problem. Also check for sidewall cracking and or bulges. Some sidewall cracks are normal in trailer tires but should be checked periodically for depth and signs of cord showing. Cord showing or numerous deep cracks indicate that it is time for new tires. Once a tire becomes five years old, it bears close watching.

Storage: When storing your trailer for a long period of time, like over winter, try to move it on a regular basis to avoid getting "flat spots" where the tire contacts the ground. If possible, set the trailer on blocks and reduce the air pressure in the tires. Some people even remove the tires and bring them indoors for the winter. If you do leave them outside, cover them to reduce damage from the UV rays of the sun. Trailer tires do have built-in UV protection, but coating them with a product like 303 Aerospace Protectant or Sun Block For Tires will help protect them. Both are available at camper dealers and in catalogs.

Understanding and taking care of trailer tires isn’t a highly technical subject, but it’s worth learning what little there is to know. This knowledge can keep you off the shoulder and on the road and can help you avoid that dreaded event, the Camper Breakdown!

For information on 303 Aerospace Protectant and a free sample, go to: http://www.303products.com/main.php?infopage=protectant