To set the record straight Nitrogen has less moisture than the air we
breathe. When a tire heats up it expands. The less moisture in a
tire the less expansion. Tire expansion or overinflated tires MAY
increase fuel economy (by decreasing rolling resistance) slightly...
BUT as a tire expands the contact patch (rubber on the road) decreases
causing your traction, handling, and ride comfort to diminish. An
over-inflated tire is also more prone to puncture or to damage (ie
when you run over a pot hole, etc). The guy from Costco just didn't
quite have his facts straight... but he is headed in the right
direction, and we know that it is NEVER possible that someone could
have their facts straight but the person listening to the sales pitch
was the dummy that couldn't accurately recall or didn't understand the
concept........ no this is not possible........