I can't be bothered with using the Cummins engine just to air up my tires.
By the time I drag out the 50 foot hose, hook it up to the air supply fitting in the driver's side fuel/LPG bay compartment, start the engine, rev it up over 1000 rpm and build the pressure up to 120 psi, and then having to keep the engine compressor running so you have enough PSI, THAT is way too much work versus using my portable Husky 155 psi compressor.
Get the compressor out, plug it in and turn it on. Connect up the clamp-on air chuck and let the air begin! A good compressor, various air chucks and a good calibrated air gauge is all I need.
My fronts are at 105 psi and my rears are at 110 psi. The Husky does a fine job plus it get used for many other tasks besides just airing tires.
I still carry that 50 foot hose but it has not seen the light of day since I first tried using the on-board sir system.
Now for those that don't have the room to carry a compressor, then I guess the engine compressor would be the next best idea for airing tires.
Dr4Film ----- Richard