If my tires are already filled with nitrogen, then can I "top it off" with regular air, or am I not supposed to mix nitrogen and air. I check my tires monthly, and fill it to the recommended pressure, so I would hate to take it some where just to put in a psi or 2.

 

I agree with what Dreyfus said and even though mixing air from your garage compressor with nitrogen in your tires is not a problem it does certainly lessen the advantage of having nitrogen filled tires over time. I think the benefit you get from closely monitoring your tire pressure from home as you are doing is at least as great as using nitrogen and is another reason I don't have nitrogen in my tires.

The only local dealers that I know that say Lexus fills all it's tires with nitrogen are those that sell the nitrogen fill as a dealer add-on.

Dave Mac

 

And therein lies the main--if not only--reason why I'm not gonna run out and fill my tires with nitrogen any time soon...the benefits/gains are definitely not worth the costs required to realize them.