Have you ever noticed cars with mysterious green valve stem caps on their tires? If you have, you may wonder why some people choose to use them. Don't worry — a lot of people have the same question, and many people give the wrong answer when trying to explain the phenomenon. The first thing you need to know is that green valve stem caps are not a fashion choice.

Sure, green is a great color, and it's probably many people's favorite, but that doesn't matter. In reality, green valve stem caps indicate that the tires are filled with nitrogen instead of standard air. People do this for a variety of reasons, including the potential to lose a tiny bit less air pressure over time, resulting in things like mild improvements to fuel economy and tire life.

However, those improvements are minimal, and filling your tires with nitrogen does cost a bit of extra cash. So, if you're running regular air in your tires, don't feel like you need to rush out and switch to a different gas. That said, if you do prefer to fill your tires with nitrogen, you may be wondering about the best place to get it.

Depending on your area, you probably have more options than you realize. Costco is a popular choice, and we'll cover its tire nitrogen service shortly . However, we'll also discuss a few other locations that commonly keep nitrogen on hand and the services they offer.

Finally, as a former professional auto repair technician and a lifelong gearhead, I'll go into a little more detail explaining why p.