From the pages of I RVing: Spring 2023

Reading the Writing on the Wall

Speed indexes, tire types, and everything you need to solve the riddle of RV tire selection.

Living life in the fast lane? Going 70 mph down the stretch? You may need to slow down, O road king of Babylon! The writing on your tire’s sidewall will tell you that not all RV tires are rated for safe operation at highway speeds. And, if you own an RV, chances are high that you will primarily be driving it on a highway. For example, if you have an ST (special trailer) tire that does not feature a speed index rating, the top speed is presumed at 65 mph. Knowing your load and speed index rating (as well as the age and dependability of your tires) can not only improve your trip, but it can also save you from a serious tire failure. So here’s a guide to help read the writing on your tire wall—and find the right RV tire if your old one has been weighed, measured, and found wanting.

What’s Written on the Sidewall?

On a tire’s sidewall, manufacturers state the maximum specifications that their tires can safely operate. But it’s not always easy. Some specifications (like the speed index) may be omitted because they are not a federal requirement. The information found on tires is also constantly evolving. (Example: Manufacturers slowly moving away from load range and instead using load index.) To boot, the load range is provided by the manufacturer with different meanings. For example, one tire’s load range E will not have the same maximum weight as a different tire. In contrast, load index is simply the load index number multiplied by four. Much more straightforward, right? When determining the correct load index for your RV, take a look at its GVWR (gross vehicle weight rating), which is affixed to your RV. This weight can then be divided by the number of tires on your RV. If you have an RV that has a GVWR of 10,000 pounds with four tires, you’ll want to make sure that the tire’s load index is more than 2,500 pounds.

(It also doesn’t hurt to go a bit over.) For example, my travel trailer has a GVWR of 9,290 pounds, which would equate to around 2,322 pounds a tire. However, this travel trailer was equipped with Goodyear Endurance tires rated at 2,833 pounds, which is about a 20 percent load. This provides a better peace of mind that the tires are able to handle the RV’s load without issue. If you have dually tires on your RV (common with Class A and C motorhomes), you’ll need to take into account that dually tires have a lower load index than single tires. This is due to excess weight that will be applied to a single dually tire if the inner or outer tire fails. Most tire manufacturers will place a speed index rating on their tire’s sidewall. Common speeds found on RV tires are from G (56 mph) to N (87 mph), the most common being L (75 mph).

For your safety and those around you, do not exceed the manufacturer’s speed index rating. In addition, always obey local and state traffic safety laws, which may require you to drive slower than the posted speed limit if towing or traveling in a motorhome. Personally, I prefer driving 55 to 60 mph and knowing that I will reach my destination safely. After all, it’s all about the journey, right? So how do you find and understand the load and speed Index? This information is posted right after the sizing information on the sidewall of your tire. For example, an ST225/75R15 117/112N is an ST tire that has a width of 225 mm, with a sidewall height of 75 percent of the tire’s width, that fits on a 15-inch rim, has a maximum weight rating of 2,833 pounds in a single tire configuration or 2,469 pounds when in a dually configuration (see picture), and a speed rating of 87 mph. While the size rating is easily understandable, the load and speed indexes are not. As the name implies, you can find your tire’s load and speed indexes on an index, of which many are accessible online.

Which Type of Tire Is Right for Me?

While you can use LT (light truck) tires on a travel trailer or fifth-wheel, ST tires are recommended because they offer improved fuel economy with shallower grooves, improved stability due to stiffer sidewalls, and reduced swaying at highway speeds due to high rigidity. You will find that most ST tires have a simple tread pattern designed for low rolling resistance. This is because ST tires are not used for steering or acceleration, removing the need for increased traction that a more complex tread pattern provides. For Class B and C motorhomes, you’ll want to use LT tires. These tires are designed to provide ride comfort, as well as traction for maneuvering and acceleration. For Class A motorhomes, you will want to use commercial or RV-marked tires. Both LT and RV tires come in different tread patterns. More complex tread patterns provide additional traction for traveling in muddy, wet, or snowy conditions. However, complex tread patterns will lower your fuel economy. If you plan on traveling in more harsh climates, such as Alaska, you will want to have the appropriate tires that can handle the roads you’ll experience. Not doing so can increase your chances of getting into an accident or having a tire failure.

When Is It Time to Replace a Tire?

When a tire reaches five years of age, you should consider replacing it, and any tire that is 10 years or more (including a spare tire) should be replaced. Tires typically have a 5-year warranty, depending on the manufacturer. When using a tire outside its warranty period, the tire manufacturer will not provide the coverage that it would provide if under warranty, like if a tire failure occurs. The age of your tire can be found on its sidewall. For tires manufactured after 2000, the date code is represented as the last four digits at the end of the DOT number, pictured above. The first two digits represent the week the tire was manufactured and the last two represent the year. For example, the code 4620 represents the tire was manufactured the 46th week in the year 2020. If you would prefer an app to help you find out the date, you can add the four-digit code into several apps found online. TireMinder.com features a tire age calculator on its website under tools.

Which Brand Is Best?

There are multiple brands out there that have been around now for nearly, or over, 100 years. When choosing the best brand and tire for your RV, it really comes down to personal preference. If you look through online forums, you will find thousands of people who are adamant that their tire is the best (or worst). As far as popularity goes, the common tire of choice in the towable market is the Goodyear Endurance, while in the motorized market the Michelin XRV is king. The best (and possibly worst) part about everything having a rating these days is that you’re able to look online and find the exact tire that fits your needs, then look at the star rating to see how many people have had a positive experience. Keep in mind that even if you find a tire with a 5-star rating, it’s still possible that you may run into issues. But if you chose a tire from a reputable brand, you know that on the unlikely chance an issue does occur, they’ll back the product.

Best Buys

Last but not least is deals. RV tires are expensive and most of us belong to one or more clubs, such as FMCA, Good Sam, Escapees, etc. These clubs may offer specials on specific brand of RV tires, along with a slew of other benefits. If you do not belong to a club, it may be worth looking at the cost of membership for the savings alone. Some even come with gas savings benefits, so like traveling on a correctly inflated tire, you’ll be saving money every mile. Just a bit of sage advice.


weighing and Measuring Tire Pressure

New and old tires, STs, and LTs all need to maintain proper air pressure to perform. Here’s some wise counsel: Employ a trustworthy TPMS device.
TireMinder A1AS TPMS
TireTraker TT-600 / 6-Wheel
Tire Monitoring System

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