How do you know?

[KnuckleHead]

Was wondering how you know when you need to air down for a trial? And if one needs to air down.... how do you know what psi you should go down to?
Also when do you use 4H vers 4L?

[4Runninfun]

This is kind of an open question and you'll get quite a few responces. I'll give you my general MO.

I'd use 4hi when I'm on an improved road and the conditions on the road demand extra traction. Such as snowy/icy roads are going to be the biggest need for 4hi. Also if you're on a trail that isn't hard but may have some washouts that may flex your rig up a little. so in general 4Hi for extra traction.

4Lo is generally for when a great deal of extra traction is needed or, extra power is needed. Also when the need to approach obstacles slowly occurs. When you enguage 4lo the transfer case is going to be selecting a higher gear than normal. My low gear in my 4runner is 2.28:1. which means that i'm going to get slightly better than double the torque output. it also means i can go slower by a similar factor.

As for airing down the primary reason to air down is to gain a larger footprint from your tire. thus increasing traction resulting is less wheel spin. How low you go depends on the terrain. Generally you are going to start seeing traction advantages at about 15psi depending on the weight of your rig as well as your particular tire. Most tire and wheel combinations can hold the bead reliably until 10psi, below that you may or may not run into troubles depending on your individual combination.

The second reason to air down is for ride quality. the further you air down your tire the more the rubber of the tire will absorb the bumps from the terrain. once again the ride quality will noticeably improve around 15psi and get softer from there.

However there is no "magic number" for all rigs in all situations. best thing is to get out and experiment for yourself. When experimenting with tire psi for trails it would be best to make sure you carry a spare and some sort of method to be able to air up if you wind up blowing a bead.

[Brody]

Bottom line, you don't really 'need' to air down for any trail. That said, many people air down for all trails no matter the difficulty level. Many times this is mainly for comfort as a tire normally run at 32 psi on the street is going to just be a lot more comfortable on a bumpy road at 20psi.

There are no real universal rules of thumb for airing down, either, but it usually isn't until you get below 20 psi that you actually experience any benefits. On a hard, rocky trail where traction and performance are real issues, airing down to 14 pounds and lower is common. All of this is determined by tire size, vehicle weight, sidewall thickness, regular tire street pressure, etc.

For instance: Randy commonly runs 50 psi on the street. He has a 9,000lb rig. He airs down to 30 or a little less and the trail and gets decent sidewall flex. I run anywhere from 25-32psi on the street and my tires don't even start to flex until I am down to 14lbs or below.

Part of it is drivability, too, like between trails. I can drive between trail on the highway at 14 lbs up to 40-45mph. 10lbs and I have to slow down to 25-30 as the truck wallows around too much...So what I would do is to air down to around 18-20 pounds the next time you do a run and see what you think. Or park it in the street and start letting air out until you see a visible bulge in the sidewalls and then see what your pressure is.

4Hi and 4Lo:

I am seldom out of 4Lo when I am on the trail. I have 5 forward gears and a hand throttle and 4Lo makes for a nice combo. If the road is flat or smooth enough, I am in 2WD as I am going faster.

Users choice. I hate shifting up and down between 4Hi and 4Lo as I have to stop my truck to do it. I max out 5th gear Low range at around 20 which is about as fast as I am going to go off road before I simply switch it to 2WD as then I am on what amounts to a county dirt road anyway...

[KnuckleHead]

I'm reading a lot about airing down on ruff terrain.... but what on snow? Do you air down then also?

[Brody]

I'm reading a lot about airing down on ruff terrain.... but what on snow? Do you air down then also?

I treat snow the way I treat a harder trail. I air down to around 14 or so psi. If I don't get good traction with this, which is always dependent on the kind of snow and conditions, I will air down a little more. My rig isn't light anymore..there is only just so much airing down that is going to do any good. It gets to be kinda like Fat Albert putting on shoes that are bigger to walk in the snow...He is still fat and heavy....

If you have chains, you are going to be running at street pressure anyway to keep the chains tight.

[Ace]

LOL, in my Sammy I air UP to 16psi:2c:

In snow I'll run 6psi... for trails 6 to 8, or if it's short or I'm too lazy to air up I'll just run what their at.

At Walden sand dunes I run 5psi. Made a HUGE difference going from 6 to 5.

[Mporter]

Arg! I had something to add to this thread but in reading the good posts above....I forgot....

Just if you guys wanted to know :)

[Chris]

I air down pretty much for comfort, sometimes I don't bother on an easy trail but I'm not in to really hard stuff where airing down makes a difference on obstacles. I use 4L all the time on trails, 4H maybe on dirt roads/snow. It's kind of trial & error figuring out what your truck likes the best.

[Doobie]

Airing down can also help to wrap your tire around an obstacle. For instances, a rock with edges. A fully inflated tire will not give and the only traction is directly at the bottom of the tire., where as an aired down tire is more pliable, so more tread is on the ground, (a larger foot print) More on the ground, the more traction.

[Mporter]

Airing down can also help to wrap your tire around an obstacle. For instances, a rock with edges. A fully inflated tire will not give and the only traction is directly at the bottom of the tire., where as an aired down tire is more pliable, so more tread is on the ground, (a larger foot print) More on the ground, the more traction.

Yep like he said....you can find some rock crawling pictures/videos of tires that are just hugging the rock.
Im too lazy to find one.....so just watch some youtube vids...:rolleyes:

[Andrew]

I typically run at about 12psi. My MTR's have a pretty strong sidewall so even at 12 they don't look a ton like they are aired down. I pretty much air down for every trail, easy or not, because I like the smoother ride.

Also - airing down is important on rocky trails because your tire will flex. If it's at street pressure, the tire will resist the rock and the rock will win, and you can puncture a tire. With the tire aired down, it will have enough deflection that it can wrap around the rock or give instead of resisting.

[Brody]

Here are a couple of links that help to clarify the 'mystery' of airing down.

This first one is for sand, but the concepts apply to all phases of wheeling:

http://www.4x4now.com/sfjun96.htm

And here is another:

http://www.off-road-outdoors.com/tire-pressure.html

[Mporter]

http://rockmidget.smugmug.com/photos/546992574_DrWAT-X2-1.jpg

There's some good sidewall flex!

[Patrolman]

As some already stated, I only air down when it is necessary. Usually a good compressor is no-where nearby when I do back country trails in Utah. Driving 60+ miles on the highway with low tires is dangerous. I only air down if I know there will be air nearby afterwards or if I MUST such as in sand.

Regarding hi/low, I run 4hi on snow/ice/mud/sand. Anywhere that requires some speed and momentum. 4lo is where I want to go slower such as more technical trails. Usually with my 4 cylinder, 4lo is dictated by the inability of the motor to produce enough power to move itself in 4hi. 4hi when possible, 4lo for slow/safe procedures or when saving the clutch is an issue.

[Pathrat]

I really like when the basics are posted and reading all the facts and opinions.

Lo vs Hi is sometimes an issue for me too. I end up in 4Lo on downhills because the stock gearing sucks and I don't want to ride my breaks. Of course on harder trails, I am in 4Lo most of the time.

We air down for comfort even if it is only to 25psi. When I was a new newbie, I asked the air down question on another forum and was told if I wasn't at 15psi I was wasting my time. Whatever. I did notice that my tires took a beating when I did not air down enough on a tougher trail.

Seems to me that you can air down to what you are comfortable with, without risking popping a tire of the rim, and if you have air on board or very near by.

[Mporter]

Seems to me that you can air down to what you are comfortable with, without risking popping a tire of the rim, and if you have air on board or very near by.



Not to "one-up" you, but the technical term is called "Losing a bead".....just thought i'd throw that out there since it's a common term.

[4Runninfun]

ahh crap we got a technicality nazi! :D

[Pathrat]

ahh crap we got a technicality nazi! :D

Beads...I wear those sometimes.

[WINKY]

:rolleyes:

[KnuckleHead]

Want to say thanks for all the input so far.... I have checked out all the links that have been posted up and find that there is good reading on it... I always like to here from others as to want they do....
So I guess next summer I will have to hit more trials and do a little playing around to see whats good for me and me rig....I plan on doing On Board Air sometime this winter
Again thank you all for your input and advice...

[Andrew]

For onboard air, I recommend CO2 over a compressor, unless you can fit one of those york compressors or similar that runs off your engine. CO2 is faster to inflate, and an added bonus is that you can run air tools off of it without issues. Most of your portable compressors won't be able to keep up with the 90PSI required for that.

But it is all personal preference in the end and what works best for you and your budget.

[KnuckleHead]

For onboard air, I recommend CO2 over a compressor, unless you can fit one of those york compressors or similar that runs off your engine. CO2 is faster to inflate, and an added bonus is that you can run air tools off of it without issues. Most of your portable compressors won't be able to keep up with the 90PSI required for that.

But it is all personal preference in the end and what works best for you and your budget.

I talked it over with Pete and and he said I can convert my A/C to a compressor... that sounds like the better way to go seeing as I have no real need for the A/C... I just roll down the windows and get the fresh air....

[Chris]

Pete helped me with that on mine and it's a nice setup. My regulators on and off are somewhere like 90 and 120 psi. so I get good pressure and don't have to lug around tanks that need to be refilled.

[Medic-5150]

ahh crap we got a technicality nazi! :D

ahahaha

[KnuckleHead]

Pete helped me with that on mine and it's a nice setup. My regulators on and off are somewhere like 90 and 120 psi. so I get good pressure and don't have to lug around tanks that need to be refilled.

You gave me the notion to talk to Pete after we talked about yours at Wheeler Lake. I'm thinking of putting a 5 gallon tank where the spar tire was. Thinking that might make it so I don't need to rev the motor for while I'm airing up.

[WINKY]

i am looking into putting a york on brutus, hand throttle too. once i get my welder the possibilities are endless!

nice thing with a diesel they like to stay at constant rpm's and locking it 2500rpm engine wont hurt it at all for hours!

[Chris]

I didn't find any advantage to using the tanks so I pulled them. ;)