Just put Crossfire tire equalizing systems on our trucks. I was never comfortable with thumping to determine if tires were adequately inflated. Added benefit is also the equalizing function between the two tires. The range, on the Crossfire, from being overinflated and underinflated seems to be about 3 pounds either side of the horizontal line which represents exactly 100 pounds. 

My question is this; how much does the carrying capacity change if tires are underinflated by say 5 pounds or 10 pounds? I'm wondering if running at 10 pounds underinflated only decreases the carrying capacity of the tire by a few hundred pounds if it is necessary to adjust all that often? The system is like having a tire pressure gauge hooked up all the time. Guys that thump cannot tell the difference between 100 and 90 so why should I care, especially since the tires dual mate is of equal pressure.