lloger said:I asked the guy at Costco the same question and he said it wouldn't hurt anything to add air. He also mentioned about going up in high altitude and that the nitrogen didn't expand.
I wouldn't worry about altitude and air in your tires, we did a trip to the highest highway in the USA, to the top of MT Evans, Co. Plus we have been to the lowest highway in the USA, to the bottom of Death Valley. Funny thing, no tire problems. End of test.