Admit it — the only time you pay attention to your car's tires is when one of them is flat. After all, it's easy to assume they're doing fine as long as they can get you from point A to point B. But ...

So you notice one of your tires is low and you pull into a gas station to use the air machine. Or maybe you've got one of those nifty portable tire inflators. But wait! The air machine is asking for ...