I use the SPEEDFLATE 4 tire system to air down and up. Quality unit with a very accurate gauge that reads in tenths. Coiled hoses cut to the length of your wheelbase, so that it doesn’t lay on the ground. QD connection for the valve stems, equal pressure, etc. It was the best one I researched and was the least expensive. With the discount code it is about $160. No more f’n around on my knees one tire at a time and checking each tire’s psi. I highly recommend this unit.
The BEST 4 Tire Inflation/Deflation System. Introducing Speedflate! - YouTube