Gas in tyres: myths and facts

1. “A tyre inflated with gas reacts far less to the ambient temperature, and keeps a more stable pressure”

Not true. Under the second of Gay-Lussac’s Laws (1808, also known as Charles’s Law), at constant volume the ratio of pressure to temperature is a constant for any gas. The key word is ANY gas. That includes nitrogen, helium, oxygen, hydrogen, and any mixture of any gases at all. So, for example, if you inflate wheels at a temperature of +20 with any gas at all (including ordinary air) to a pressure of 2 atm, then when the air temperature drops to +10 the pressure in the wheels will fall by the same amount regardless of which gas was pumped into the tyre, because the tyre’s volume stays practically unchanged and will certainly not depend on what the gas is made of.

2. “A tyre inflated with gas is much softer and grips the road better”

Honestly, to anyone who learned even a little physics at school, this should sound like complete nonsense! What affects how “soft” a tyre is and how well it grips the road? Correct: PRESSURE and the tyre’s own construction. You could also add the state of the road surface. If anyone is still telling themselves that some magic gas’s molecules can “squeeze aside” over a pothole, just remember that all of this happens once the tyre is inflated to a given pressure! Once the required pressure has been reached, what the gas is made of can no longer affect the tyre’s springiness in any way at all!!!

3. “Gas is much lighter than air, so it will save you a lot of fuel”

A killer argument. Given that the average wheel holds well under 100 grams of air, and gas has at least some weight too (incidentally, what is usually pumped in at tyre-fitting shops for an extra fee is a nitrogen-based mixture, and there is already 75-78% nitrogen in ordinary air, so the weight difference is bound to be minimal from the start), I hope by the time I retire I will have “saved” enough for a new little green valve cap!

4. “Gas in tyres prevents oxidation and substantially extends the service life of the tyres and the wheels”

A very serious argument. Except someone still needs to work out how to fit an airtight bag over the outside of the wheel too, and pump that full of gas as well, so that no harmful air gets anywhere near the wheel! Or even better, put the whole car in a gas chamber: that would be safer still. But seriously, even if you only ever drive your car at weekends to the bakery round the corner, your tyres wear out dozens of times faster than they oxidise and “age” from the inside.