DrewE wrote:
Do be careful to make sure that both tires on the same side of a dually axle are at the same pressure. (I know this isn't exactly related to your question, but it's kind of important anyhow.) If they're at different pressures, one of the two will have a slightly larger diameter, and one or both will be forced to slip a little as you drive and they will wear relatively quickly. I aim for within 1/2 psi of each other.
It's not nearly so important that the tires on opposite sides of the vehicle be precisely equal in pressure, though of course that's generally the intent.
That is a good point and they do make filling hoses that allow you to tie both duels together so that they are both filled to the exact same air pressure. I use the Psiclops XL180 but there are other brands out there.