Full size rigs-Airing down

Tex68w

Beach Bum
So for those of you running rigs in excess of 7000 lbs (i.e. 3/4-1 ton trucks/suv's) with tires 35" or larger on non-bead lock wheels, what pressures are you running when you air down? I run 50-55 psi under normal conditions and I have aired down to 30 psi just messing around, but I am not sure what the threshold should be on these larger rigs!? Is 15-20 psi safely doable or should one stay at 25-30 psi or higher?
 

RPhil

Adventurer
I run down to around 15-18 for beach driving in my pig and have no issues. My tires are ~34”. No issues thus far but I'm not wheeling hard when on the beach.
 

SexyExy

Observer
What specific size rim diameter are you running? The bigger the rim diameter, the less you can safely air down since you have less sidewall with the bigger diameter rims. Less sidewall means you need more pressure to keep the tire from de-beading as it flexes.


On 35" tires with a 16" rim, you'll have no problem going down to 12 psi while driving slow, like 15 mph or less. This is a great sand & flotation pressure. For the "oh ********" moments, I've gone down to 10 psi to get through some super soft sand terrain in my big heavy Suburban with 35" tires on 16" rims. For two tracks, gravel and washboard roads, I would run anywhere from 16 psi to 18 psi when below 25 mph. As the speeds go up, you need to increase air pressure for handling stability and heat resistance.

On 35" tires with 17" rims, maybe a low of 13-14 lbs...with 18" rims maybe a low of 14-15 lb for soft sand, snow, rock crawling, etc.

The best thing you can do is find an open dirt or gravel lot near your house, lower the pressures and see how the truck reacts. When staying under 15 mph, you can go very low and the bead will retain unless you're playing baja racer or hit a very large rock against the sidewall when turning.

In the comfort of your driveway you should remove one of your tire/wheels and deflate it and break the bead so you can learn to re-seat the bead with your air compressor, etc. Every tire and rim has its own idiosyncrasies and you won't know what that is until you actually try and seat the bead. It doesn't matter how many books or videos you watch, hands on technique is key. Think of brain surgery, you can read books and watch all the videos of a procedure, but until you crack open a lot of heads to physically do the job you won't get good at it. Tire repairs and re-seating beads is something that has to be practiced on the vehicle you drive. A one ton truck tire and wheel is going to have different tendencies than a 15" rim with P rated tires on a RAV-4.

When re-seating the bead, the most important thing to remember is to remove the valve core while seating the bead....it is so restrictive that is slows the air volume down too much and makes re-seating the bead very difficult.

If you're at 30 psi, you might as well leave the tires at 55 psi....not going to help. You have to get under 20 psi to start seeing a softness in ride for washboards and even lower for flotation on sand, snow, etc. As I stated above, the faster you drive and the heavier your truck, the more psi you need to hold up the weight. One my F350 4WD with a diesel, when running empty on the street I keep around 50 psi in the front and 45 psi in the rear. This makes the truck ride very smooth at highway speeds. As my weight increases due to loads or trailer weight I increase the pressures for stability and heat resistance.

Experiment, experiment, experiment...practice, practice, practice......you don't want to find out you can't seat a bead when on a muddy hillside road in the dark on a Sunday night.
 

Tex68w

Beach Bum
Good points! I run 65 psi when towing, I need to get ahold of someone with Forscan in my area to change the low air pressure settings in the computer so that I don't get the light and warning message constantly when below 55 psi. My wheels are 20x10" and I am running 37x12.50's. I feel like I can run 20 psi safely, I guess I need to try it out on some back gravel roads this weekend. My only concern for the lower pressures on non-bead lock wheels is when we run PINS, there are sections of extremely soft sand where you have to carry speed in excess of 20 mph to keep your flotation on these heavier rigs.
 

PJorgen

Desert Dweller
Good question and I'll be interested in reading the responses.

Here's my thinking FWIW. My rig is about 8700lbs - 3/4 ton PU with a Four-Wheel camper, 18" non-beadlock wheels with 33" tires. Like the OP I run 50psi front, 55psi rear on the street. When I air down I usually halve the pressure to 25 front, 27 rear. That doubles the contact patch area and halves the ground pressure. That's a pretty big bang for your airing down buck and is still a reasonable tire pressure. I've used these pressures at speeds up to about 25-30 mph with no problems. On occasion I've gone lower but kept the speeds much lower as well.

Having said all that, my rig is big and heavy so I don't do any serious wheeling. Mostly dirt roads and the occasional sandy wash.
 

LR Max

Local Oaf
Good rule of thumb (and vehicle specific). At street pressure, measure the distance from the ground to the bottom lip of the rim. Record this measurement (so if you are running 35s and I assume 18" wheels, this measurement would be ~8" or so). Now take 75% of this measurement, which for our example would be 6". Now air down the tire until the distance from the ground to the bottom lip of the rim is to your 75% measurement. Record this tire pressure, and that is what you need to air down to! Or at least start here and then you have a ballpark to play with.
 

Joe917

Explorer
At 9 tonnes I'm probably one of the bigger rigs here. I run 95psi 315 80 22.5. Dropping to 60psi smoothes washboard and helps with traction. I have gone down to 30 psi in sand, it makes a big difference. I have not lost a bead so far. A friend runs 365 ?? 20 and will drop to 7psi (yes 7)in deep sand, I believe he is about 6 tonnes. He has lost the bead usually while turning.
 

leelikesbikes

Adventurer
I run single digits in the deep snow, 12-15 off-road, and 35 on the street with 37's on factory wheels on my standard cab hemi ram. A narrow steel wheel holds a bead better than a wide aluminum one.
 

Buliwyf

Viking with a Hammer
Yep, big wide wheels are poseur clues.

Those base model 17x7.5" steel wheels are solid gold off road. The "minimum rim width" is a safety spec for on road.
 

dirtnadvil

Member
If you are running E rated tires they shouldn't be driven on the blacktop lower than 45 psi. The low pressure causes them to heat up and eventually come apart. Ive learned this lesson...........twice now:yikes: Both times it required body work. Airing them down doesn't help much BTW due to the stiff sidewall construction.
 

Joe917

Explorer
If you are running E rated tires they shouldn't be driven on the blacktop lower than 45 psi. The low pressure causes them to heat up and eventually come apart. Ive learned this lesson...........twice now:yikes: Both times it required body work. Airing them down doesn't help much BTW due to the stiff sidewall construction.

If my L rated tires air down fine E's should too!
 

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