Quick—how old are the tires on your Airstream?

If you’re like most people, you haven’t thought about that in a while, and you might even be wondering why you should be thinking about it now. The short answer is that tires eventually get too old for safe use, even when the tread still looks good.

For recent owners, here’s the shocker: having bought a new travel trailer or motorhome doesn’t actually guarantee that the tires are new too. That’s because the Airstream may have sat on a dealer’s lot for a while, or (if it was a trade-in) it might have had the tires swapped.

Tires have a finite lifespan even if they aren’t being used, and that lifespan begins from the moment they are manufactured, not when they are placed into service. There’s really only one way to be sure of the manufacture date of your tires, and that’s to get up close and personal with your tires.

Every tire has a date code imprinted right into the rubber on the sidewall. It’s four digits, printed in a little box like the one shown in the photo. This box only appears on one side of the tire, so it’s possible that if you can’t find it on it on the outside, you’ll have to slide under the trailer to look at the tire’s other side. Bring a flashlight and a notepad so you can record the date code for each tire—they may all be different.

Deciphering the four-digit code is easy. The first two digits are the week the tire was manufactured, the second two digits the year. For example in the photo above, “2115” means the tire was manufactured in the 21st week of 2015. That’s mid-May, 2015, which isn’t bad because the tires were purchased in August. It’s not unusual for tires to sit around in a warehouse for a month or three between manufacturer and purchase.

If your tire only has a three digit code, replace it now! Tires with 3-digit date codes were made before the turn of the century.

The tire industry has varying recommendations on when you should replace tires. Some manufacturers say four years, others say as long as ten years. But the actual lifespan of a tire varies depending on how it is used, so if your tires have seen a rough life (lots of storage time, exposed to the sun, under-inflated occasionally, lots of potholes, etc) you should probably err toward the side of caution and replace them after four or five years—no matter how good they appear.

New buyers should check date codes too. The dealer will probably be surprised that you even knew to ask about the tire date codes (and imagine their faces when you slide under the trailer to look at the date code yourself!) but at the same time this shows that you’re a serious buyer and you have done your research.