Tire Pressure

bobg333

Senior Member
Joined
Oct 5, 2007
Messages
123
I was camping on the beach last week in Baja and got into some soft sand that I could not move forward in. So I dropped the pressure in 5# increments until I could get her to move. 25# finally did the trick. My question to the group is how far down could I have gone? 15#? Also what pressure are you using for general off-road driving. My rig has BFG All-Terrain TAs.
 
BFG AT's here too...

On ragged little trails like in Death Valley, Utah and Colorado, I drop down to 18PSI. If I go as low as 16PSI, I don't worry about it... On a tire with stiffer sidewalls, like with an MT tread, you could drop down to 12PSI or lower. I wouldn't go that low with an AT, especially in sand. Too easy to peel a tire off a rim...

16-18PSI with the BFG AT is a good range for most off-road situations.
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Makes sense when you are on the trail, but how does everyone air up for the highway drive home?

We're planning a loop to Soldier Meadows from Gerlach to Alturas then back 395 over Thanksgiving.
 
Most carry an air compressor of some type, or a C02 tank. Or at least a handful of quarters for the air-fill at the nearest gas station. ;)

I carry one of these and will use it to air back up after our trip into Saline Valley in a few weeks. There are several other options, some bigger & beefier for using air-tools on the trail if necessary.
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It really depends on your vehicle. On my Jeep I'll go down to 8 psi, even lower in the snow but theres no way I'd even think about doing that on my truck.

I have quick air II in the Jeep, just a little cheapie auto parts store compressor for the truck. It fills tires in beer increments.
 
BFG AT's here too...

On ragged little trails like in Death Valley, Utah and Colorado, I drop down to 18PSI. If I go as low as 16PSI, I don't worry about it... On a tire with stiffer sidewalls, like with an MT tread, you could drop down to 12PSI or lower. I wouldn't go that low with an AT, especially in sand. Too easy to peel a tire off a rim...

16-18PSI with the BFG AT is a good range for most off-road situations.
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Whoa. 18psi on an E rated tire for hard surface trails? Is that because you want the rubber to flex so as to no have a rock puncture it? I've driven all over UT, from slick rock to loose sand to rocky trails, without ever going under 45#. Have I just been lucky not to puncture a tire? (I get the "floatation" effect of airing down for sand, but for rock?)
 
You know how Utah is Brett... You can go from slickrock, to washboards, to sand, to step stairs all within a single mile. So yeah, I air down for whatever may come, for better traction, for a smoother ride, to resist punctures, etc.


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I can't say if you've been lucky so far, or if I've been overly cautious... But I can say I prefer an 'aired-down' ride in most scenario's.
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I run E rated tires as well and I agree with what others have said. I air down to as low as 15-lbs if I am on very rough road. When I first started doing this I got out a lot in different types of terrain to look at the tires to see what was going on. Here is what I found. On roads that are very rough like the photo above 15-18 psi is great. In Sandy conditions 15-psi is great. On roads that have very sharp cobbles or boulders that are arranged in random order....like you would encounter in Death Valley and some parts of the Sierra....I usually only go down to about 25 lbs. I do this because I don't want to expose the sidewall to damage....this is especially important in off camber situations.

I use a small portable compressor (Master Flow MF-1050) to air back up.....and yes it occurs in Beer increments as Craig stated. I believe several members on this site have this compressor, They are very reliable.

I would say that if you do air down as low as 15-lbs or even 20-lbs you should know how to put your tire back on the bead should you peel it off. There are several techniques out there some faster than others and some safer than others. You can do it with a couple of ratchet straps (safe/slow method) or you can use a can of starter fluid (not as safe/fast method). I have used both methods and both work just fine......but you do need to practice it. When I learned how to do this at home it took me several tries/hours with each method before I actually became comfortable with it.

Cort
 
I'm learning here, because I am thinking about this all wrong maybe. First, I was weary of airing down E tires so low thinking that any tire needs have at least ~25% of its max pressure or risks overheating (from extra friction), damaging the sidewall or falling apart (needing the air pressure to hold its shape and support the vehicle's weight). Guess I was wrong about these?

Second, I had sort of figured that air pressure wouldn't matter much to a puncture wound. If a rock is sharp enough and at the correct angle to cut the rubber, then it will. Whether the tire is softer or harder isn't going to matter much since it is still (literally) tons of weight pushing on the sharp edge.

Do I have this all wrong? Man, I'd love to see the Mythbusters test this one out.
 
You know how Utah is Brett... You can go from slickrock, to washboards, to sand, to step stairs all within a single mile. So yeah, I air down for whatever may come, for better traction, for a smoother ride, to resist punctures, etc.


701817972_ZqpAE-O.jpg



I can't say if you've been lucky so far, or if I've been overly cautious... But I can say I prefer an 'aired-down' ride in most scenario's.
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Funny, in that pic, I wouldn't hesitate to take that with 50# in my tires. I'd actually prefer the firmer control and stability of the stiffer tire (but not enjoy the hard bounce). I need to rethink this air pressure stuff.
 
Your speed has a lot to do with whether or not a rock will puncture your tire. If you do air its normally expected you'll be driving a lot slower giving the tire time to form around the rock.

You don't want to get back on the highway until you've had a chance to air up.

I can tell you from years of rock crawling just what a difference it makes. Not just in a softer ride but in traction. Two identical rigs, one airs down one doesn't. One climbs right up an obstacle the other spins his tires. Deep snow and sand is where it really shines. You can't afford to dig down.
 
With my off road Scout I have run everything from 40 - 2 psi and it all comes down to what speed you want to be able to go. The faster you want to go the more psi you will need. I've peeled tires off the bead at 18 psi, but I was hauling butt and rounding corners/hitting rocks way to fast.

Weight is also a huge factor - the more you weigh the more psi you'll need to keep your tires together.

I run lower pressure in all off road conditions as it hugely increases traction, way more than you'd think until you try it. If you've never tried it start at 20 psi, then drop a few pounds at a time as you get more comfortable.
 
I'm learning here, because I am thinking about this all wrong maybe. First, I was weary of airing down E tires so low thinking that any tire needs have at least ~25% of its max pressure or risks overheating (from extra friction), damaging the sidewall or falling apart (needing the air pressure to hold its shape and support the vehicle's weight). Guess I was wrong about these?

Second, I had sort of figured that air pressure wouldn't matter much to a puncture wound. If a rock is sharp enough and at the correct angle to cut the rubber, then it will. Whether the tire is softer or harder isn't going to matter much since it is still (literally) tons of weight pushing on the sharp edge.

Do I have this all wrong? Man, I'd love to see the Mythbusters test this one out.



Here's a far from scientific example, but relevant I think... If you blow up a balloon so it is full or nearly full and push a pin into it, it will quickly puncture it & pop. However, if you blow up a balloon only halfway, then push a pin into it, the balloon will deform around the pin quite a bit before it punctures and pops. It's similar with a tire... especially at any kind of speed on a rock filled trail. Less air in the tire will allow the tire to deform over a sharp rock, while a tire at max PSI won't deform, possibly leading to a puncture.

The 'hard bounce' you mention is another factor that is eliminated with an aired-down tire. What you don't see on the photo I posted, is an extreme drop-off on the driver's side (that was taken at the exit/entrance to Elephant Hill in the Needles Dist. of Canyonlands) A few hard bounces coming down that narrow rocky stretch potentially could have bounced me uncontrollably off the side to a likely demise or severe injury.

So rather than leave my tires aired up, resulting in a ride down that section like sliding down a staircase on your butt - a jarring, semi-controllable experience, I aired down my tires, eliminating any hard bounce/recoil from the rocks, so I "flowed" down that section like pouring water down a staircase instead.

Again, I apologize for my less-than-scientific examples here but they're a couple of decent analogies... The softer ride on aired down tires makes it easier on the kidneys (SunMan is right) the dental work and the vehicle & camper which aren't forced to absorb all of that recoil from the hard bounces. I never used to air down going over the Alpine Loop and it was like riding a horse, bouncing in the saddle all day. Now I air down and it is much more tolerable. Still a bouncy ride but kinda in slow-motion. Much easier on me, my passenger and vehicle. Same in the Maze District, Death Valley, etc. These 3 off-road areas are notoriously rough on tires, shocks, leaf-springs, coils etc. but airing down makes them more tolerable.

Peeling a tire off the rim is a concern, but as UglyScout mentioned, those happen primarily at high speeds while taking a sharp turn, like when out in sand dunes or in deep snow. It can happen anywhere I suppose, but primarily those are the type of places & conditions where peeling a tire off happens.

Give it a shot sometime and see what you think. Just make sure you have a way to air up, or that there is a gas station nearby with air, before driving too far on pavement back home.
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What you don't see on the photo I posted, is an extreme drop-off on the driver's side (that was taken at the exit/entrance to Elephant Hill in the Needles Dist. of Canyonlands)

:eek:
You did Elephant Hill with a camper or just the entrance? That is a pretty aggressive trail if I remember right.

As long as airing down will still allow the tire to support all the weight, I'll definitely start doing that. I carry a small, wimpy compressor, but a gas station with air is rarely more than 30mi away.
 
I did the whole trail with the camper... came up from Beef Basin & Dark Canyon, into the Needles, down the Silver Stairs, through Squeeze Play, backed up the switchbacks and crawled out over Elephant Hill -


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It was a little stressful in spots but I'm glad I did it. Glad, because now I know and I don't have to do it ever again. ;)
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You the man, KC. Elephant Hill is rated a 7 on the 10pt scale. They say modified vehicles only beyond 4 or 5. Don't think I'm brave enough to try it. Were you running on fumes assuming that was all on one loop?
 
Well I kinda cheated... I have an ARB locker in the rear and I used it... a lot! :)

We were ok on gas by Elephant Hill. We had filled up down at Hite Marina, then rode up to Natural Bridges and over Beef Basin until we got into the Needles. From there we rode up through Lockhart Basin & Hurrah Pass into Moab, and I was definitely on fumes by then.

Beautiful area. If I had run out of gas and been stuck out there, I can't say I would have minded very much. :cool:
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Well I kinda cheated... I have an ARB locker in the rear and I used it... a lot! :)

We were ok on gas by Elephant Hill. We had filled up down at Hite Marina, then rode up to Natural Bridges and over Beef Basin until we got into the Needles. From there we rode up through Lockhart Basin & Hurrah Pass into Moab, and I was definitely on fumes by then.

Beautiful area. If I had run out of gas and been stuck out there, I can't say I would have minded very much. :cool:
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That's not cheating....that using you head :D
 

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