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Also, I have both a shop compressor and the portable 12 volt one I keep in my truck.  With the digital readout that your can preset to the fill level, I find I prefer using the 12 volt one even when I'm at home and have access to the faster shop one.  I can set it and walk away.  

And even with 18" full size truck tires, it has had no problems filling them from completely flat.  Now, it takes a little longer than the shop compressor would, but I get to set it and walk away to do other things whereas I'd have to babysit the shop compressor.  I also enjoy that it is portable and always in my truck.  You're not always at home when your tires need air.