What's the right tire pressure?

In the RV world there's always a lot of chatter about tires. It might seem strange that tires are such a big topic, since most of us barely think about the tires on our car or truck unless they need to be replaced.

For travel trailers in particular, tires are a big deal for several reasons:

1. You can't feel anything if a tire goes flat while you're towing (which is precisely why a TPMS is essential).
2. Trailer tires take a lot of stress in turns, and from things like hitting curbs.
3. Trailer tires tend not to get used as much as car tires, so they often "age out" just while sitting in storage.
4. A tire failure on an Airstream trailer can cause an incredible amount of collateral damage to the aluminum body, which is very expensive to repair.

One of the biggest questions is simply, What's the right tire pressure?

If you have an Atlas or Interstate motorhome, the recommended pressure is easy to determine. Look the "Tire and Loading Information" placard located (typically) on the driver's door jamb, or check the Mercedes-Benz Sprinter Owners Manual that came with your motorhome or details. Keep in mind that there might be different pressure recommendations for front and rear wheels.

For a travel trailer, it can also be very simple—or not. The Federal Certification Label attached to the outside left of your Airstream tells you everything: the size of tires the trailer requires, the maximum load the trailer can carry, and the recommended tire pressure.

For a late model trailer, it's going to probably say 80 psi for the tire pressure, which is the maximum pressure the tires should have when "cold" (meaning before you start driving).

For most people, there's nothing wrong with using 80 psi for the Goodyear Endurance tires. That's what the majority of our customers choose to do. But sometimes people look at Goodyear's "Load/Inflation Information" table, which is published online, and see that they could run lower pressure based on the weight of their trailer. Then, somebody online claims that lower pressure is "better for the Airstream," or that it gives a "softer ride"—and suddenly the choice of air pressure gets a lot more complicated.

First off, let me dispel the myth that lower air pressure is better for the Airstream. It might be in some cases, but you have to weigh the trailer at a truck scale to know for sure.

Sometimes people point at a broken pop rivet on the interior as evidence that the tire pressure should be lower, but that's just a supposition. Pop rivets sometimes break and it doesn't necessarily mean anything (and you can easily replace them yourself with a simple tool, as we've demonstrated in this video).

(If a lot of things are breaking in your Airstream on every trip, there are other possible problems to investigate.)

Too-low tire pressure can be even worse than too-high pressure, so before you take the advice of someone who says you should lower the pressure in your tires, you should do some homework. The first step is to know how much the trailer weighs including all the stuff you've packed.

I talk about the process of weighing a trailer briefly in The Newbies Guide to Airstreaming, and in much more detail in The (Nearly) Complete Guide to Airstream Maintenance, 2nd edition. If you don't have a truck scale nearby, you can estimate the typical loaded weight of the trailer by adding:

1. "Factory Manufactured Weight" from the Federal Certification Label
2. Estimated weight of your belongings (clothes, gear, food, tools, etc)
3. Weight of water in the Airstream (the number of gallons in the holding tanks and the water heater @ 8.3 lbs/gallon)
4. Net weight of two full propane tanks (typically about 60 pounds) 

Compare that total weight to the Goodyear Endurance Load/Inflation table and see what pressure you could run if you wanted. (Keep in mind this example applies only to Goodyear Endurance tires. If you have another brand, don't use this table.)

For example, let's say your full load was about 6,300 pounds on a trailer with four wheels, and your tires are the Endurance ST225/75R15 model. That's 1,575 pounds of weight per tire. 

According to Goodyear's table, you could set your tire pressure as low as 30 psi. But should you? I wouldn't unless I was experiencing some significant issue, like the tires are wearing in the center. Using the bare minimum tire pressure leaves you no leeway if there's a leak in any tire, or if you change altitude significantly during your trip, or when the outside temperature changes significantly. You'll have to check and adjust the tire pressure before each tow, if you run at the minimum possible pressure.

I generally recommend customers stay above the minimum allowable tire pressure for one key reason: if you ever have a leak from a nail or screw, you'll have a lot of buffer before the tire goes critical and starts to shred itself. That gives time for you or your Tire Pressure Monitoring System to detect the problem, which could save you from an expensive repair.

Photo by Jahongir ismoilov on Unsplash