Hi beerman, some answers to your questions.
I may have covered nitrogen in tyres on here before so if I have my apologies to anyone who's already read about it.
I have to start by saying these are my own opinions and I'm sure for every one who sees no benefit in nitrogen, there'll be someone who does.
Nitrogen was used by Hans Tholstrup at Bathurst in a Falcon in the early 70's. It was a sponsorship exercise for CIG (now BOC??).
Since then nitrogen has been used in Northern Australia in trucks and road trains and over the last 15 years or so has been sold as a benefit by Bob Jane T-Marts and more recently, Jax.
It normally costs (about $5 - $6 per tyre) at the point of sale. The benefits are supposed to be cooler tyre operating temperature and less pressure loss because the nitrogen molecules are larger than the hydrogen/ oxygen mix (air) used normally.
As I advocate you should check your tryes every couple of weeks to pick up any slow leaks, whether or not you use nitrogen is a moot point.
They will run cooler but how much effect that has on tyre wear is debatable. Will it save you $5 / tyre? Studies by RAC experts and major tyre companies would suggest not.
Of course, if you have a punture you have to pay to have nitrogen put back in after the repair.
I've not run across the "free nitrogen" offer before but the cynic in me suggests the cost would be added in somewhere to the cost of the tyres.
I can't see how the tyre would affect your fuel economy as it's the pressure in the tyre which affects rolling resistance and thus, economy.
Having said all that, 2i30's is an advocate of nitrogen and I respect his experience, too. Maybe he can chime in here with some current feedback.
Now, as to green tyres. There are any number of these on the market now and makers claim better fuel economy through lowere rolling resistance from carcase design and/or tread compunds. Independent testing indicates perhaps as much as a tank of fuel saved over the life of the tyres. If you are the type of driver who accelerates gently and smoothly and backs off the throttle well ahead of time this sort of saving will add to your benefits. i suspect most of us aren't though.
As to extra benefits on highway driving? Probably just a magnification of any saving based on miles covered.
