Here's a hint: Filling your tyres with nitrogen is a rip-off
Filling your tyres with nitrogen? Some tyre retailers are offering to fill your tyres with pure nitrogen gas - for as much as $40 per tyre. Sometimes the gas is called 'anhydrous' nitrogen - which just means 'dry' (ie, without humidity). Overall? Bad idea.
...and if you believe all that, I have some swamp land in the Florida Everglades that's on sale for the bargain of the centuryFilling your tyres with nitrogen: what it costs
You'll pay up to $160 for a set of four tyres filled with anhydrous nitrogen gas. The fact is that the air you're breathing now is 78 per cent nitrogen - so you get 78 per cent of the benefit of filling your tyres with pure nitrogen by just filling up with FREE compressed air at the servo. (The remainder of air is 21 per cent oxygen and 1 per cent other gasses.)
Filling your tyres with nitrogen: What the retailers claim
Tyre retailers often say aircraft (including fighter jets) have tyres filled with anhydrous nitrogen. This is true. Aircraft operate at temperatures as low as minus 50 degrees C (at altitude). At these temperatures, humidity in air freezes, and could lead to imbalance problems on landing. This is unlikely to affect you and your car, unless you plan on driving at 30,000 feet...
Tyre sellers also claim dry nitrogen is used in Formula One racing. This is also true. Elite car racing uses pure nitrogen gas in tyres because it has what engineers call a higher 'specific heat' than air. This means that there's very slightly less pressure variation in the tyre for any given heat input. In F1 racing, where not just every thenth of a second, but every hundredth of a second, counts, such extreme measures are worthwhile. On your road car? Filling your tyres with nitrogen is a joke.
The third claim tyre retailers make is the purported slower permeation of nitrogen through the tyre's rubber - in other words, they say, pure nitrogen leaks more slowly through the rubber walls of the tyre than compressed air does. This is also true. Actually, it's more of a half-truth. Nitrogen gas molecules are slightly larger than oxygen gas molecules. So they do leak more slowly through the tyres' walls. However, leakage through the rubber itself is not a particularly significant cause of pressure loss in a tyre. Faulty valves, poor bead sealing and minor punctures are a much more significant mechanism of slow leakage. So this purported benefit, although based in fact, is also a joke.
In any case, if you simply check your tyre pressures once a fortnight at the local servo (and top up any low tyres using the free compressed air) slow leakage of the kind purported to be prevented by filling your tyres with pure nitrogen is relegated to being a non-issue.
Filling your tyres with nitrogen: the verdict
Verdict? You have to be kidding. Agreeing to filling your tyres with nitrogen is a complete waste of time and money - unless you're Boeing or an F1 team. If you're a normal driver, save your money and use free compressed air instead - no matter how vocally your tyre retailer defends the nitrogen concept. They're advising it just to boost their bottom lines. There's no tangible benefit for ordinary drivers.