I just mounted mine on my Specialized Dolce Comp 48". I tried it on the down tube (straight down from the seat post) but didn't like it there, because sometimes my leg would rub on it. So then I mounted it on the slanted tube (I don't know the technical terms here) that goes from the middle of the bike (near the pedals) up to the front fork. I mounted it just to the left of my water bottle holder that is on the inside of that tube. It fits just fine, and is out of the way--I checked to make sure my toes didn't brush it as I pedal (if you mount it there, be sure not to put the mounting bracket over the brake/shifter cables--I just ran the bracket under the wires, so they can move freely).
So that's my suggestion. I could have mounted it on the underside of the top tube (the one horizontal to the ground from seat to handlebars) but then it would have interferred with getting my water bottles out, since that is a tight fit with two holders as it is.
I do like the pump--it sure works nicely.
Whoever said last man standing wins never asked a girl to play!