I got my smart in the middle of August and I am very satisfied with everything about the car. Not one negative experience with it, and it continues to offer surprises. I have consistently gotten better mileage than it is rated at, and the higher the octane I put in the better it gets.
Starting a week ago, my tire pressure warning started to come on for the first few blocks on my way to work in the morning as the temperatures have been falling to frost point and below. After a few days like this, it began to stay on all the time. I knew I had to get to an air pump and boost the pressure.
I was going to purchase a tire pressure gauge and fill my tires this weekend but then I remembered what my father had taught me a couple of years ago, and called around to a tire shop to see if I could get nitrogen put in my tires. I found one and now I once again have proper pressure in my tires that won't loose pressure ever unless of course, if I get a flat.
Nitrogen does not expand nor contract the way that regular air does, and it only cost me 4.00 per tire to replace the air with nitrogen. Now my car drives like brand new again, and I don't have to worry about my tires. Having had nitrogen before, I know my tires will wear much better, and my mileage will increase slightly again by having consistent proper pressure.
It is well worth the cost to have this done, and will save the cost back in tire wear and mileage. I did not want to have to deal with my pressure monitor warning me every change of season and worry about what pressure was really in my tires even when the warning wasn't going off. Also, I didn't want to deal with running to a service station and dealing with pumping air all the time. I have gotten very used to not having to go to the gas stations so often and I want to keep it that way.
My last car had green valve caps to denote that the tires had nitrogen, which tells service stations that they don't have to check the tire pressure. This time they put green washers under my existing valve caps, for the same reason.
I highly recommend you think about this for peace of mind and economy. I was shocked to feel how much better the car feels with nitrogen in the tires, I wonder how low they had gotten by the time the warning went off, but it is a major difference.