What is “airing down”? Why do you want to do it? What pressure is best? Tire air pressure is not a “one size fits all” concept. When I’m pulling a heavy trailer, I want my tires aired up, especially the rear tires, up around 80 psi. My buddy, when driving his jeep on old skidding trails, will drop his to around 10 psi. Even if I were to follow him in my F-250, I can’t go that low; I’d be sitting on the rims.
So what off-road air pressure do you need? Well, let’s talk.
Why Air Down?
If you ever go out with a group of off-road enthusiasts, you’ll see them park their rigs when they leave the pavement, and walk around dropping the pressure in their tires.
Generally, high pressure keeps your tires’ shape, so you don’t have excessive wear on the sides of the tread, over the sidewalls. Your tires stay cooler because they aren’t constantly flexing as they roll over the pavement. Cool tires translates to longer wear and keeps them from breaking down, or blowing out at high speed. If you are pulling a load, or carrying a load, the higher pressure lends to greater stability- the tire doesn’t want to roll to the side or squish.
All of that is great, when you’re cruising to or from your destination on those never-ending slabs of pavement.
Dropping the pressure in your tires, however, is useful when you go off-road. The lower pressure helps increase the contact patch, squishing out the tread so more of it touches the ground. This helps when you want to grab more of the surface, handy when you’re climbing a hill on loose terrain. Low pressure also helps the tire float over soft surfaces, such as sand or mud. Obviously, you’re still going to sink some, but it will likely keep you from having to pull out the shovel when your buddy was too lazy to adjust his pressure. If you’ve ever noticed off-road tires that have tread blocks on the sidewalls, now you know why they’re there.
What You Drive
If you are in a light rig, such as a Jeep Wrangler, you can go pretty low on pressure. If you’re running oversize tires, you can go even lower. I’ve read stories of guys dropping the pressure down to around 6 psi when they’re rock crawling or playing in the sand.
If, on the other hand, you drive a heavy-duty pickup like mine, even with oversize tires you’re going to want to keep much higher pressures. I’m running 35″ tires on 20″ rims- not ideal for off-road, but sufficient for me since my truck has to play multiple roles. I don’t like to run less than 35 psi in the back, and 45 psi in the front even when I’m off the pavement.
The reason for the disparity front-to-back is the extra weight in the front. Those tires support more truck, so they need more pressure.
Where You Drive
Are you just going to stick to graveled, well-traveled forest service roads? You can leave your pressure at highway settings, or you can drop it some to smooth out the washboards. Running in four wheel drive can help when you need to climb a hill. The combination of medium pressure and 4×4 will help maintain the road. If I know I’m going to spend a few hours on the gravel and I’m not hauling, I’ll drop my pressure to 45 psi rear, 55 psi front. This helps smooth out the bumps, but doesn’t negatively affect handling or cause excessive temperatures.
Snow and ice are a different animal. There are two schools of thought here, involving either a wide, low-pressure tire to float and grip more surface area, or a narrow, higher-pressure tire to cut down through loose snow and put more weight on a smaller patch. Both ideas have merit, so depending on the kind of snow you see either may be a better solution.
If you see deep, fluffy snow you may want to float over it, packing it under your tires to keep you from digging in too far. If you see snow that’s very wet, but not as deep, perhaps a smaller contact patch will yield better traction; you won’t be as likely to ski with your truck when you can dig down to the gravel underneath. Honestly I’m not entirely sure what the best answer here is. Leave me a comment below if you have an idea.
How You Drive
If you like to drive fast, hard into the corners and digging up the trail with a heavy foot, don’t drop the pressure to far. You’ll end up pinching the tire between a rock and the rim, tearing the rubber, or you’ll pull the bead off the rim when you corner too fast and you’ll have to stop to re-seat it, if you have the proper equipment.
Of course, if you’re taking it easy, letting momentum and low gearing control your speed, with your foot hovering over the brake, you will be able to go pretty low and not worry (as much) about getting a flat.
A great rule of thumb that I saw in a forum is this: Drop a 1″ bar across your track, and drive your tire onto it, centered. Let the air out until the tire kisses the ground on either side of the bar. That’s a great place to be until you really get enough experience to go lower.
Adjusting Pressure Down, and Up Again
So you’re at the beginning of the day, your buddy hops out and dumps the pressure in all four of his tires in just a few minutes. Meanwhile, you’re still working on the first one. Turns out he used a tool designed for airing down, one works with the valve stem pulled so pressure drops fast such as the ARB E-Z Deflator, or perhaps he can set the pressure automatically with something like the Real 4×4 Tire Air Deflators. You grabbed a stick and pushed down on the valve stem, periodically stopping to check the pressure. Ugh.
Then, at the end of the day, you stop before getting back on the highway to air up again. There are many solutions for getting air back into tires. You can get a nitrogen tank that is pressurized with several gallons, enough to pump your tires back up to pressure very quickly. You can also carry an air compressor that runs off of your battery. Don’t mess with the little ones that plug into a cigarette lighter. Those don’t have enough power to pump up a 35″ tire, or if they can, it will literally take you a couple of hours to get it done. Another solution a compressor mounted directly to their truck, one they can use for air bags, hubs, or any number of air-driven tools.
Do some research and decide what kind of solution works best for you. I have a Viair 400p. It works fast, isn’t too expensive, and will last for years.
Let’s Wrap Up
Knowing how to drop your tire pressure when you hit the trail is a useful concept. It yields better traction and a softer ride, so you (and your partner) are not worn out at the end of the day and still have energy to set up camp for the night.
Having tools such as a good deflator and an air compressor to do it fast and still get back up to pressure when you hit the highway makes it completely worthwhile.
If you have a question about anything in this article, or if you have experience and would like to chime in, feel free to drop a comment below.