Wayne,
the other Wayne, not me.
Good point about the amps! I agree that the more current it draws from the 12 volt source (battery) then the faster it will pump up the tires, assuming similar losses, etc.
You would think that with 3 years of high school electric shop and 2 years of EE at Cal Poly I would have remembered that. But, like many of us programmers say, it's a hardware problem. I only do software.