I currently have the largest 12v air compressor I can find, the kind with the alligator clamps that go on the truck/RV battery. At best, it works marginally, and I've been trying to figure out how large an AC powered compressor I need to get to about 125 psi on a tire. What is confusing is the data on the compressors...horse power, gallon size of the tank, max psi it will pressurize, etc. Many of the smaller 12v pumps, that plug in the cig lighter advertise 150 psi...which might be true if blowing up an air mattress. Some of the big AC models advertise only 80 psi...I don't get it. If any of you smart folks out there can explain what all this means, I'd appreciate it.