The normal air that you fill in your tyres consists of 78% nitrogen, 21% oxygen and 1% other gases and water. When you fill your tyre with nitrogen the pressure inside the tyre remains stable. This is because the nitrogen molecule is larger than the others, it doesn’t seep out of your tyre quickly. It in fact lasts 3 to 4 times longer than if you didn’t have your tyre filled with nitrogen.
nitrogen filled tyre has less water vapor in it unlike compressed air which has a by-product of water. That’s why at high temperature, a tyre full of compressed air will expand much rapidly at an unpredictable rate. But a nitrogen filled tyre will expands at a much slower rate due to the absence of water content.
Nitrogen is a colourless, odourless, tasteless, and non-toxic gas that forms about 78% of the Earth’s atmosphere. The claimed benefits of nitrogen over compressed air for inflating tyres are that it: Reduces the tyre’s running temperature. Keeps tyre pressures more constant.