Offroad tire pressure

[BroncoAZ]

The beach I run on requires 12 psi max for any vehicle, my Tacoma and Bronco run fine at that pressure in sand. In my 5500# FSB with 35x12.5R15 tires I used to run 14-15 psi rock crawling around Moab and AZ, 12 psi was too low and I dented a couple steel wheels. When I went to 35x12.5R17 I had to keep the pressures up in the 17-18 psi range to keep from hitting the wheel on some rocks. I agree with 25 psi for Baja style driving as speeds under 40 mph, I’d probably bump it up to 30 psi above 40 mph.

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[ICUGAZN]

I'm no expert and still learning, but at Raptor Assault we ran the 35" tires at 25psi. So, on my Raptor and the couple of times I've taken my Bronco offroad, I've run between 22 and 25. That has worked for both sand and rocks for me. Of course, I've always had always had a method to air up and down at the trailhead.

 

[FlyingScot]

I too, attended the Nevada Off-Rodeo, and I could have sworn they told us they were using 25 psi, but that's close enough for government work.

With that said, what's the risk of driving up to 40 miles home from off-road fun site with tires at 25psi? (i.e. Am I destined to purchase an air compressor / or a power tank system? and yup, I know that's a different off road thread everywhere...) An no, I'm not trying to go off script here... Just want to know if its safe to drive on the street up to 60mph with tires at 25psi?

You'll see some killer setups on here that can inflate/deflate all four at once, but if it's not a regular use item, you can get something simple like this, toss it in the back when you head out and never worry about it.

You could even get crafty and put together a Schrader-to-NPT adapter, an inline bleed valve and then an NPT-to-Schrader chuck, stick it on the end and have an one-stop-shop inflator/deflator, but that won't be much cheaper than getting one of those brass jobbies.

 

[bikearch]

Has anyone measure their air pressure cold and then after or during a session...?...to measure the change.....conditions and ambient air temps should determine what pressures you run......I am a former motorcycle road racer and tire pressure regarding contact patchs are critical for fast times....i am curious to hear how critical it is for rock crawling and high speed desert at a amature level??

 

[ryridesmotox]

Has anyone measure their air pressure cold and then after or during a session...?...to measure the change.....conditions and ambient air temps should determine what pressures you run......I am a former motorcycle road racer and tire pressure regarding contact patchs are critical for fast times....i am curious to hear how critical it is for rock crawling and high speed desert at a amature level??

Going by my TPMS I don't really see much of a change when crawling. its stays about the same all the way through unless I start going over 30mph. Then it will start picking up pressure.

 

[Paul Gagnon]

There is no blanket guideline for how much to air down. You have to try different pressures depending on the terrain, your wheels and tires and your comfort level. There is also no set pressure where beadlocks become mandatory.

For my Explorer, on radials I usually run 10 psi, bias ply tires I run 5 psi, no beadlocks.

 

[jzweedyk]

I posted this before in another thread, but this is my thoughts.

Tire, pressure and wheel thoughts



It seems to me that there are a lot of questions on tires and wheels. I have never worked in a tire shop, but I have bought a lot of tires, wheeled off-road for over 20 years, belonged to a couple of Jeep clubs and have stayed at a Holiday Inn Express. Here are my thoughts, which are worth what you paid for them.

Wheel size; If you are driving a high performance sports car you want a large wheel for larger brakes and a shorter side wall on the tire (low profile) to give you quick response to steering input. (Very little sidewall flex)

If you are driving an off-road vehicle you want the opposite. A lot of side wall to soak up the irregularities in the trail, and to be able to air down without the wheel coming into contact with the tire tread. Since you also need brakes, the generally best wheel for this is 17 inches. Big enough for good brakes, but small enough for a lot of sidewall on 35”+ tires.

Tires; The size and tread pattern that will be best for you depends on what terrain you are going to be in. Knobby tires will big tread blocks and a lot of void areas are best for mud, as they can not only grip in the mud, but clean out quickly. Tires with small voids will turn into slicks in the mud, and therefore have little traction. Knobby tires can also work well if you are climbing a craggy rock face and need to grab on to the edges of rocks to get traction.

I do a lot of wheeling in Moab which has a lot of “slick rock”, which despite its name is basically sand paper on rock. So, the more rubber you put down (less voids) the greater the traction you will get.

Tread patterns are very personal, so use the one that fits your needs.

Tire size; Generally speaking, bigger is better. The downside to bigger is they are heavier, cost more and put more of a strain on vehicle components. If the tire is big, with a big tire patch, it will test other components, and the weakest link will break. Why is bigger better? The easiest way to understand this is to take it to the extreme. Think of a pebble rolling on cement and coming into contact with an expansion joint. It probably will get stuck and not be able to cross it. Now think of a 40” tire rolling on cement, when it reaches the expansion joint it won’t even slow down. So bigger tires can climb higher obstacles, give you more ground clearance, have a bigger sidewall to absorb shocks and bumps, and cross small “cracks” easily.

Tire Pressure; This is the most misunderstood area of tires. On road follow the vehicle manufacturer instructions. At speed low pressure tires will build heat quickly, and heat is the enemy of tires. Off-road is a different story. What does lower pressure do for you? One, more comfort. The sidewall can flex and absorb shocks better with less pressure. Take a tire inflated to the max and drop it a couple of feet, it will bounce back almost all the way up. Take a tire inflated to 10 psi and drop it, and it will hardly bounce. Two, wrap around obstacles for more grip. Three, increase the tire patch, which is the amount of the tire that is in contact with the ground. This accomplishes three things, one, lowers the pressure per square inch on the ground, which can keep you from sinking into things like sand. Two, gives you more rubber on the ground to increase the chance of getting some traction when climbing an obstacle. Three, lessons the chance of a tire puncture. Again, take it to the extreme. Think of a balloon. If it has hardly any air in it, you can push a pin in quite a way before it will pop. Inflate it to the max and the pin will pop it easily.

So, how low? It depends on several things. First what load range are your tires? C range will have the most flexible sidewalls, and as you go up the alphabet the sidewalls get stiffer. I have bead locks on my Jeep with 39” C range tires. However, the Jeep weighs 6,200 pounds, so if I go much below 10 psi and come down a steep grade where all the weight is on the front the tires will wrinkle up and get too close to the wheel. When I had load range E tires on it, I could go down to 4 psi before they would wrinkle too much. I like C range as it allows the tires to conform to the rocks and get a good grip.

Second what are you going to do? A gravel road will feel better if you drop about 10 pounds from street pressure. For medium trails 18-20 psi can work well. For more serious trails I go down to about 12.

Everyone always worries about blowing a bead. First, if you just had your tires remounted, wait a couple of days. That way the stuff they put on the bead to set them, will have totally dried. Low pressure too quickly may allow the tire to rotate on the rim and change the balance. Second if you are really low 8 – 12 psi, don’t do donuts or try to turn a stuck tire when it is wedged in a rock crevice. With non-bead lock wheels, I have never heard of someone blowing a bead when they had 12+ pounds of air in the tires. You CAN do it, but you will have to work at it. Even with bead locks, most bead locks only work on the outside of the wheel, it can be possible (although unlikely) to blow the inside of the wheel.

To conclude, run the pressure you are comfortable with. Experiment and try different pressures. Buy a good quality HD air compressor. You will pay more for it, but only once. A cheap one you will cuss out every time you use it. The biggest mistake I see on the trails is that most tires have too much air in them. If you are spinning your tires, they may be over inflated.

 

[Paul Gagnon]

Although comfort is definitely a factor to consider, my primary reason for airing down is to gain traction by increasing the contact patch.

More than just the size of the contact patch, lower pressures allow the tire to deform around an obstacle instead of simply bouncing off. Besides the obvious reduced resistance to mounting an obstacle, it also creates more biting points for the tire in areas that a tire with a higher pressure will never be able to contact.

 

[wjfawb0 [hacked account]]

I always keep a viair 100% duty RV air compressor in my wrangler for airing up after offroading. I run 15 psi crawling and 20 psi on rough forest service roads. I also 3D printed some deflators that I use so I can air down faster as well.

I would also recommend anyone running oversized tires do a chalk test to confirm their normal highway driving contact patch on their tires. Overinflated tires can wreck you quickly in the rain and wear them faster just like underinflated. My wrangler only weighs 4200lbs, so with heavier load range larger tires (D or E), I run less pressure than the OEM load range C tires.

I have also had tires spin on OEM aluminum wheels when crawling at less than 18psi. That was quite evident when they shook the crap out of the jeep on the way home and I had to have them rebalanced.

 

[rws]

Although comfort is definitely a factor to consider, my primary reason for airing down is to gain traction by increasing the contact patch.

Pictures tell the story quite nicely. Safe to say, if you go down to single digits you should be running beadlocks?

 

[nomnom]

i did rock crawling at 12psi no beadlocks, stock sasquatch wheels. Nothing crazy, but it was good. 15psi will be fine for mild crawling without beadlocks.

For reference, i did this at rainbow falls in colorado, near woodland park.

 

[Ibuprofen3293]

Believe it or not (for what it's worth) at Nevada Off-Roadeo they keep the tires at 28 PSI, and there are some pretty aggressive off-road conditions from crawling over boulders in canyons to sprinting on gravel roads. The guides are professional with years of off-roading experience and they seemed more than comfortable with 28 PSI. As Razorbak86 correctly points out, though, it is all debatable and please believe me when I say that you will get differing opinions on this subject from highly experienced folks. Probably a safe comment is "Air down some for comfort, but not so much that you risk losing a bead". Everything between 20 and 30 PSI is probably a good window.

I know this is a very old thread/post, but I was just at NV Offroadeo and all the (Sasquatch) broncos were running 20psi. I’m assuming they’ve adjusted things a bit since you went/posted.

Separately, I just took an off-road class led by some very experienced wheelers, and they had everyone with 17-18” wheels and 30-33” tires air down to 12psi, which seemed a bit low for non beadlock wheels. It seems like it’s a learn and “feel” decision, along with the specifics of your vehicle and terrain.

I’m thinking for low speed wheeling, my Bronco on 33s (and hopefully soon 35s) without beadlocks, should be between 15 and 20psi.

 

[jzweedyk]

I have done 12 psi all the time without bead locks. Unless you are doing donuts or lodging your tire in a wedge and trying to turn hard on it, you should have no problems. Don't try it on the day after the tires are mounted, because the stuff they use to lubricate will not have fully evaporated.

 

[jzweedyk]

See my Jan 20, 2022 post above for more information.

 

[broncosor]

Since my OP I have used my Bronco offroad a lot. From slow technical to high speed trails (60+MPH).

For high speed I like 25-28.
For very rocky slow stuff I usually keep at 20. Plenty of traction and I hate the feeling at 15, vehicle does not feel planted and is wobbly. Also makes me more comfortable when the trails open up a bit and I am taking a corner at 30mph.

YMMV

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