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Understanding Ratings and Markings on Tires for RVs and Campers

Don has been an avid traveler and motorhome owner for most of his life. He shares his experiences along with valuable tips for RV owners.

Motorhome and Camper Tires

The information in this article includes important reference data on tires that are used on automobiles as well as your RV, motorhome, camper, trailer, fifth wheel and even pop-up campers.

The data here will help the reader understand tire markings and ratings when they need to replace their older or worn-out tires.

RV and Camper Tire Specifications

The tires on your RV are as specialized in design as are those on a race car.

The ones on a race car are designed to operate at extreme speeds and provide as safe a ride as possible.

The tires on your RV are just as specialized, but with a different purpose. They are designed to carry very large loads on diverse types of roads at various speeds and still provide as safe a ride as possible.

Be sure to know your tire size, tire age and condition, and always replace them with the same or equivalent tires.

Keep in mind that as soon as tires are manufactured, they begin to age and degrade to one degree or another. This depends on how they are stored and maintained.

There are several things you should do to assure that your tires are safe, and last a long time for you.

Tire Specifications and What They Mean

RVs use a wide range of tire sizes with many different specifications that the manufacturer selected to match the specific design requirements.

When you replace your tires be sure to select tires that match these specifications.

For your reference, here are some of the markings you will see when you look at your RV tires, along with the definitions of what they mean.

You should always check with your tire dealers for the latest recommendations, as the technology for tire construction is constantly changing:

RV Tire Size - (example = P245/ 70 / R 19.5 )

The first 3-digit number 245 is the tires Section Width. It indicates that the tire is 245 millimeters across from the widest point of its outer sidewall to the widest point of its inner sidewall.

The letters in front of the 3-digit number will indicate the following;

P - indicates it is a P-metric tire and is used on passenger cars including cars, minivans, sport utility vehicles and light-duty pickup trucks (typically 1/4- and 1/2-ton load capacity).

Nothing - if blank, then the tire is a "Metric" size (also called "Euro-metric." Euro-metric sizes are equivalent dimensions to P-metric sizes but usually differ slightly in load carrying capabilities).

T - this indicates that the tire is a "Temporary Spare" ("space saver" or "mini spare") and was designed to only be used temporarily until a flat tire can be repaired or replaced.

LT - indicates that the tire is a "Light Truck-metric" size and was designed to be used on vehicles that carry heavy cargo or are towing large trailers. These are for vehicles including medium and heavy-duty (typically 3/4- and 1-ton load capacity) pickup trucks, SUVs and full-size vans. They are designed to provide reserve capacity to handle the additional stresses of carrying heavy cargo.

70 - The number after both the 3-digit number and the slash, (70 in the example) is called its Section Height or Aspect Ratio. This tire size's sidewall height (from rim to tread) is 70% of its section width.

R - The letter after the Aspect Ratio indicates the type of tire construction. For instance, an R indicates Radial construction, while a D indicated a Diagonal or Bias Ply construction. If it is a B, this indicates it is a Radial Ply construction which is reinforced with belts in the tread area.

19.5 - The number following the type of construction letter indicates the tire and wheel diameter that is designed to be matched together. Tires with these numbers have a rim diameter expressed in inches such as:

(P225/50R16 or 8, 10, 12, 13, 14, 15, 17, 18, 19, 20, 22, 23, 24, 26 and 28) They're called "inch rim" sizes and are used on most cars, minivans, vans, sport utility vehicles and on light duty light trucks. Also, tires and wheels that have a rim diameter expressed in "half" inch sizes; 14.5, 15.5, 16.5 17.5 19.5 21.5 and 22.5) are used on some heavy-duty trailers, heavy-duty light trucks box vans and RVs.

NOTE: Tires and wheels with unique rim diameters should never be combined with traditional "inch rim" tires and wheels.

Trailer Tire Sizes

Size - ( ST 225 / 75 R 15 )

For trailers, the breakdown of the numbers is as follows.

ST - Special Tire for Trailer
225 - Cross Section in MM
75 - Aspect Ratio which is section height divided by section width
R - Radial
15 - Rim Diameter in inches

RV Tire Protection covers

Tire DOT Designations

The DOT designations - DOT MJ93 NBAW 0807

The DOT - NHTSA requires that Tire Identification Numbers be a combination letters DOT, followed by ten (1980s production), eleven (1990s production) or twelve (2000s production) letters/numbers that identify the manufacturing location, tire size, manufacturer's code, and the week and year the tire was manufactured.

MJ93- The MJ indicates the Manufacturers Plant code, the 93 indicates the government size ply code.

NBAW- Indicates the Manufacturers production code.

0807- Since the Year 2000, the last 4 digits in this group indicate the week and the year of manufacture. Or 0807 indicates week-08 of year-07.

Notes on Tire Age and Longevity

Tire Age

All RV tires have a date code on them. It is generally recommended to replace any tire more than six years old, regardless of the amount of tread remaining.

If your tires still have good tread and no signs of aging, especially in the sidewalls, and you still insist on continuing to ride on them, please keep a close and constant eye on them. And please never exceed the speed limit with old tires on your RV!

Tire Wear

You should monitor your tires, ALL of them, before and after every trip for unusual tire wear and proper air levels.

An RVs tires are very expensive and you do not want to replace them any sooner than necessary.

So, inspect your tires often for the following potential hazardous problems:

  • Uneven Tire Wear
  • Cupping at the edges of the tire tread
  • Nails imbedded in the tread of the tire
  • Cuts in the sidewall of the tire

If any of these are evident, you should take your RV to your local tire dealer/service center that also services RVs to resolve the the problem.

Solar Damage

The sun can wreak havoc with the condition of your tires and it can age them prematurely which will cost you a lot of money for early replacement. Take steps to avoid direct sunlight on your tires when possible, especially when your unit is in storage.

Extend Your Tire's Life

Tire Protection

There are several things you can do to help protect your tires and extend their useful life.

Tire Cleanliness

Keep your tires clean of dirt and debris and spray them with protectant sprays, available at your local Auto Parts store, that provide some screening of UV rays.

Raise the Tires

When you are parking your RV for an extended period of time, place plastic or wooden blocks under the tires. This elevates the tires above the ground, and minimizes the tires' contact with moisture.

Tire Covers

When you are parking your RV for an extended period of time, such as in storage for a few months or at a campground for the winter, place tire covers on your outer tires, to shade them from the sun and the elements. This can help them last several years longer before they show signs of cracking and deterioration.

Warning: Buying Old Tires

I was recently walking around in one of the RV parts stores, which was actually one of the largest national tire chains.

Heading towards the counter, I passed a sign that was touting the low price of their "New but Older Date Code" tires.

Well, I was shocked. Everyone knows when shopping for a used RV or any other vehicle, one of the first things you look at is the age and condition of the tires on the RV.

And, as I have mentioned above, the material in RV tires begins to age and deteriorate from the date they are made, thus the major reason for the required date code on tires.

So, how much of a discount do you need on your OLD/NEW tires to override your need for safety when driving your family down the road. What a stupid thing for a store to do!

Good Description of Your Tire Markings

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.