It has been shown that by keeping your tire pressure properly maintained, you can improve the fuel efficiency of your car. With the gas prices still varying in price daily, it makes sense to keep the pressure as close to the mark as possible.
A tire is normally filled with compressed air, where the air contains moisture that can greatly affect pressure as the tires heat up and cool down. This will therefore change the fuel economy of your car. The more moisture in the air and the greater the temperature range, will result in the more the pressure change and worse gas mileage. Oxygen slowly leaks out of the tire as the oxygen molecules find their way right through the rubber of the tire wall. This can happen even with new tires, but becomes more pronounced as the tire ages and the rubber becomes more porous.
To help combat this from happening, the tires can be filled with an inert gas called nitrogen. Nitrogen makes up almost 80% of the air we breathe, so it’s abundant in great quantities. It also holds less moisture, and does not respond to temperature changes as dramatically as plain old air does. The nitrogen molecule is also larger than the oxygen molecule, making it less likely to leak from the tire. All of this means that a nitrogen filled tire will hold its pressure better than a regular air filled tire. This will all result in better gas mileage with less maintenance. Racing tires are often filled with nitrogen as well to help combat the changes in pressure caused by the extreme heat produced on the race track.
Do be aware though when people claim that just filling the tire with nitrogen will increase gas mileage. At the low pressures tires hold there is little difference between a properly inflated nitrogen tire and a tire properly inflated with air. Both will get the same gas mileage. The big savings is in the fact that the pressure change in a nitrogen filled tire is slower, and since most people tend not to check their tire pressure on a monthly basis, this can save you in fuel costs.
So, if you’re offered the option to have your tires filled with nitrogen, and it’s free or is at low cost, then it can be worth it in fuel savings caused by your tires being properly inflated longer. If they want to charge you more than you can afford then take a pass, but make sure you check your air pressure on a regular basis or you will end up paying for it at the pump.