It all comes down to how well it seals and stays on the valve and how strong of pressure it can handle before its problematic. Generally the kind of pump I have should be able to do 40 at least.
Very simple, as stated by Dustin. All tires lose air here, heat and contraction causes that. Buy a 10 dollar tire gauge, put it under your seat and you can use any compressor in the country. You can but them at Handyman, Goodyear and 20 other places...