Understanding Tire Codes on Your RV and RV Trailer Part One: Standard Tire Code

You will eventually have to replace the tires on your RV or trailer, and like any other vehicle you will have to know which tire is right for the job. This guide will teach you the broad categories of tires and how to correctly identify which tire you need by looking at your current tire.

All tires made after 2000 carry a Department of Transportation designation that tells you the manufacturing date of the tire. Look for the letters “DOT” followed by a string of letters and 4 numbers. The letters refer to the factory in which it was manufactured. More importantly, the numbers tell you which week and in which year your tire was made. For example, “DOT4410” tells you that the tire was made during the 44th week of 2010.

Generally speaking, motorhome tires are different than RV trailer tires due to different load sizes and cab designs. Even if a tire on an motorhome is physically the same as a tire on an RV trailer, the tire on a motorhome will be rated and described differently for safety reasons.

There are four broad categories of tires: ST for “Special-trailer”, P for “Passenger car”, LT for “Light Truck”, and T for “Temporary”. RV trailers are most likely to use ST tires, while motorhomes are likely to use P or LT tires. Besides a few exceptions, these letters will be followed by three digits, a slash, and then two more digits. The three digits before the slash tell you the nominal width of the tire in millimeters, while the first set of digits after the slash will tell you the aspect ratio of the tire, or the ratio between the width and height of the tire.

This second set of digits will be followed by a letter and another set of digits. The first letter designates the internal construction of the tire and will be either “B”, “D” or “R”, which stand for bias belt, diagonal, and radial, respectively. The vast majority of passenger car tires today are radial tires, but trailers, including RV trailers still use bias belt tires for their high load capacity. The numbers following this letter designate the diameter of the tire in inches.

Tires also have a separate code composed of a two or three digit number followed by a one or two digit/letter combo. The first digits refer to the load index of the tire, or the max carrying capacity. The second digit refers to its speed rating, or its maximum speed. There are many different codes for load index and speed rating, which can be found here and here, respectively.

Tires may also have a number of optional markings that tell you more about its specific construction, or use types such as Mud and Snow tires.

So, putting it all together, if we were to encounter a tire with the tire code “P215/65R15 95H” we would know that this it is a Passenger car tire with a nominal width of 215 millimeters, an aspect ratio of 65, a radial internal construction, and diameter of 15 inches. This tire would be rated for a maximum load of 690 kg and a top speed of 210 km/h.

As mentioned earlier, some tires are marked slightly differently, including certain LT tires used on RV trailers. Though the vast majority of tires use the code system explained in this article, the differences are explained in depth in this article.

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