Image via WikipediaNitrogen is a larger molecule than oxygen, so it does seep from tires at a slower rate than air. How much? About three times slower, which means your tires will stay properly inflated three times longer. If it’s a major inconvenience for you to check tire pressure, then by all means step up to nitrogen if you can get it cheap. If you have to pay more than a few bucks per tire, it’s just not worth it.
Why do race teams use the stuff instead of air? In racing, tire pressure is absolutely critical, and nitrogen filled tires don’t change pressure with heat as much as air filled tires do. When you’re talking about tenths of a second being worth thousands of dollars, the cost of a tank of nitrogen is just part of doing business.
