We all know race cars tend to be vastly different from our average family saloon; they have different tyres, more powerful engines (obviously!), no need for back seats or extensive boot space. So it will come as no surprise to hear they even fill their tyres with a different gas. You probably fill your tyres with air. That’s a mixture of oxygen, carbon dioxide, nitrogen and small amounts of a few other things. Race car tyres are filled just with nitrogen.
Nitrogen expands and contracts at a more even rate compared with standard air. Considering the speeds which race cars tend to travel, any small changes in tyre pressure will have big effects on both traction and handling, which could easily change the outcome of a race! When races last for a long time (as with Formula One or Nascar races), the temperature of the track can vary considerably, so the constancy of nitrogen pressures can make a big difference.
Why does nitrogen maintain its pressure so much better than normal air? For a start, air contains small amounts of moisture. The exact amount varies throughout the day dependent on the weather conditions, and even small amounts will result in significant changes in tyre pressures during tyre fittings throughout the race, or on the same car but on different race days. The driver needs to know how the car will handle in order to get the most out of it, so dry nitrogen is used instead.
Interestingly, nitrogen is also used for similar reasons on aircraft where it is of paramount importance that the tyre pressures don’t vary too much with different external conditions. An aeroplane travelling at different heights will be surrounded by air at differing pressures and temperatures. In fact, the temperature can drop as low as -40C, so you don’t want there to be any moisture at all in the tyres as it would freeze and cause issues on landing.
Is there any reason why you would want to fill your own car tyres with nitrogen? There are definitely benefits, so it is up to you to weigh those benefits against the costs and make your decision. The lack of moisture in the nitrogen results in less corrosion on your wheels, and as nitrogen molecules are larger than oxygen molecules, your tyres will maintain their pressure for longer. The downside is that you will first need your tyres emptied of air before being filled with nitrogen, and to maintain the benefits, they would always need to be topped up with nitrogen.