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Yes, from some reading that I did on nitrogen fills some time ago, I understand that, with a properly done nitrogen tire fill, you are still only going to end up with about 92 or 93% nitrogen, and, since air already has 79% nitrogen, the additional nitrogen after the nitrogen fill is actually quite small.
At the temperature and pressure of a typical tire, both air and nitrogen will behave as 'perfect gases' and will follow the perfect gas law, I.e. PV=mRT, where the only term which is different between air and nitrogen is the Gas Constant, R. R=286.9J/kgK for air and 296.8J/kgK for nitrogen. Therefore, assuming that the tire volume does not change, according to the perfect gas law, the pressure of the tire will be more sensitive to the temperature if the tire is inflated with nitrogen, as compared to the tire being inflated with air. The tire pressure will be about 3% more sensitive to temperature if it is inflated with nitrogen.
If you are concerned with tire pressure changes with temperature, you will be better off inflating your tires with CO2. CO2 has a R value of 189 J/kgK. With CO2, your tires pressure will be 34% less sensitive to changes in temperature. That will be a measurable improvement.
We don't charge for nitrogen if that makes you feel any better, however it's pretty sad where some techs cut corners and most of the time it's the older guys/Master techs that been doing this for a while.
