Were the tyres cold when you inflated them at the servo? And warm when you got to the other place? Air pressure goes up as the tyres get warm you know, which is why you should always stick to either cold or warm pressures, and not mix the two Nitrogen has got to be the biggest **** in tyres these days. One, when you top up the pressure at a servo/wherever you're putting normal air in anyway, Two normal air is 70% nitrogen anyway, and Three if nitrogen leaks so much less than air, all you have to do is fill with normal air and wait for the oxygen to leach out leaving you with nitrogen anyway. For a race car, MAYBE it is worthwhile. For a road car, the extra $50 or whatever that the tyre place charges you for it is MUCH better spent on new spark plugs, oil change, or anything else which actually contributes to the health of your car. I agree with what Hiro has said here. Servo tyre inflaters are a bit off, not that much. Pretty sure they had to be calibrated before being put to use like that. If it is overinflated like that and the tyre blew or damaged itself the servo would somewhat be liable, so I doubt they are that off. Also theoretically nitrogen is a smaller molecule than oxygen, so therefore it would leak pressure at a faster rate. Race cars would use pure nitrogen because then pressures can stay more stable at high temperatures. Much higher than what street driven cars would even reach. Going abit off topic sorry. If you are looking for a new tyre, you should ask yourself whether longevity or performance is more important..