Bad, long, washboard roads get my attention. To take the edge off, I'll air down from my pavement pressure of 65 PSI, all around, to 35 PSI, on my E-rated Nitto Ridge Grappler 285/75R16 10-ply tires, on my Cummins/Hawk combo (8,700 lbs split equally on both axles - the Cummins diesel is heavy enough to keep the front axle the same weight as the rear with a slide-in Hawk shell on my flatbed). When airing down I use
Coyote automatic deflators preset to 40 PSI (my tires inflate/deflate +/- 5 PSI, the differential between a sunny, hot afternoon and cool night and morning temps). The Coyote deflators are adjustable from 1-65 PSI if you want a lower or higher preset.This takes me just two minutes for all four tires and is easy enough and the Coyotes are excellent with accurate repeatable results. I know I can go lower, but don't want to risk sidewall damage or losing a bead unnecessarily. At 35 PSI my tire rim is only 1/2 inch lower to the ground and the sidewall is not compromised. I suppose I'm playing it rather conservatively. I also go slow on washboards and rougher roads, regardless of whether I'm aired down. or not. The oscillations of a washboard might allow me to go faster if it helps to dampen the ride. But generally, slow is usually easiest on my truck and on me. Of course it does take a longer time to get from A to B, but the tires don't heat up as much and the sidewalls have held together well over time. I've only had one puncture in the last few years on service roads, and that was clean through the middle of the tire tread on a front drivers side tire, and caused by a sharp, long lag bolt hiding in a pothole. Also, I don't air down on forest service roads mainly because my tires have plenty of traction and don't spin in most circumstances, and because I drive slow enough on the rougher sections as to not put a tremendous amount of shock loading on my suspension. When I'm ready to air up again, after a few or after a lot of slow miles on a miserable corrugated road I pull out my
Viair 400p air compressor, which I love, and air up back to 65 PSI. This takes me about 16 minutes to add 30 PSI to all four tires (~ 4 minutes per tire).
Ocassionally, if the road is slick with slimy mud or slick with icy snow or I need some extra traction while beginning to climb a slippery grade of loose rock and dirt or snow or move through an obvious wet, muddy patch I'll drop into 4WD to get through the dicey parts and not air down. I don't want to rehash this whole 4WD vs 2WD thing here, but in my case my truck is equipped with part-time 4WD, so staying in 4WD is not necessarily preferable for me on mostly dry, switchback dirt roads where I have decent traction. The type of forest service roads that I tend to drive along don't really resemble extreme, crude, narrow, wonky Jeep trails. With part-time 4WD as many older trucks have, the truck will tend to understeer, unless on a slick surface, and also, the drivetrain components will wear out prematurely if we leave 4WD engaged all the time on dry roads with traction, unlike full-time 4WD as I understand it. I can certainly see the benefits of full-time 4WD and might use it more frequently if I had it, but since I only have part-time 4WD with both a high and a low gear range available, in addition to a manual 5 spd. tranny, I'll only use my 4WD on dicey surfaces and will stay in 2WD, which has never been a problem for me while driving the forest service roads of the Northern Cascades to the Southern Rockies, unless I see a real need to drop into 4WD.
Rich