About a fifth of air is oxygen, and the oxygen molecule is smaller than nitrogen; it works its way through tyre rubber faster over time. A tyre filled with nitrogen therefore holds its pressure longer. The second difference is thermal: moisture in ordinary air expands as it warms, so pressure moves on a long run, whereas dried nitrogen moves less. The gap is small in town driving and becomes visible on long runs and heavy vehicles — on a truck tyre, steady pressure means both fuel and tyre life. One thing should be said plainly: nitrogen does not make pressure checks unnecessary. A nitrogen-filled tyre still wants checking once a month.
- Pressure stays steady for longer
- Moves less with temperature — noticeable on long runs
- Clear effect on fuel and tyre life for heavy vehicles
- No substitute for pressure checks: still check monthly
Common questions
Can ordinary air be added to a nitrogen-filled tyre?
It can, and it does no harm. The mixture is simply diluted, so the advantage of nitrogen shrinks.
Does it really make a difference on a car?
In town driving the difference is small. If you cover long distances often, or you are not in the habit of checking pressures, it earns its keep.
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