What exactly does the nitrogen do?
I've had nitrogen in my tires for about 2yrs.
Although there are conflicting reports in the press, one benefit is the tire pressure does not change regardless of hot/cold temperatures. The nitrogen molecule does not react like oxygen. My car has a TPMS (tire pressure monitor system) and in 2yrs it has not reported any change. It also seems that the ride is more firm, without being rough, over various surfaces.
Another benefit reported is tire wear. My Pirelli P-Zero low-profile tires have lasted 26,000 miles, mostly highway, but I'm not sure if that's low, average or high. It does mean I don't have to spend the big-bucks to replace them as often.
I noticed a better ride (my friends may say I drive aggressively
) within a few miles after picking up my car. My dealer recommended the nitrogen after the owner had tried it in his Audi A8L for a couple of months.
note: the tire needs to be inflated & deflated a few times to get the proper % nitrogen. Some dealers/mechanics/tire shops have been reported to only inflate the tires once. This does absolutely nothing, but they'll charge you for doing so.
My simple answer would be, it depends on what you drive, the tires you use, and the type of driving you do. I would think the average vehicle/tire/driver would not see a big difference.
I do not have any scientific sources to refer to, but the above is my experience... and in all things, YMMV!
Regards,
Voyager