Subject: how much does the air in a basic car tire weigh?

someone at my work was ordering tires and having them ground mailed. he asked 
me if he would save money on shipping if they shipped without the air in them. 
i told him that the weight was negligable. but it did get me wondering just how 
much does the air weigh.
basic 15" rim @30 lb/sq.in.
ive search the net and done some work on it myself but am unhappy with 
myresults.the best i found online was that the air in a tire "doesn't weigh 
much" any help would be appreciated. thanks in advance.----jason klingele 

Re: how much does the air in a basic car tire weigh?