Airing Down

Click on any picture with a border for a larger view!

    Here it is April 22nd, it's 88 degrees outside and I am trying to remember what
I learned and what I observed last weekend in three feet of snow.
The first thing I learned is when you can't see your wheels and you're winching, and you stop forward motion - stop winching.  (I didn't, and blew a tire and snapped my drag link in half!)

(As I started to write this I found I was ranting and raving.  So, I think I will divide it up into different rants and raves.)

In this article I will rant about tire pressure.

I have heard in a roundabout way from several people that I am considered one of  the better drivers in the club.   At the risk of getting a swelled head (it may be too late for that) I will agree that I am better than most. I have met plenty of drivers from around the country that I consider better than myself.  I find that I am still learning.  One way I learn is by listening to people who are better than I.  I also watch where they go and how they go.  I ask why they went that way. I not only let them spot me, I try to understand why they had me go there. I did not emulate the guy that had the most wheel spin, or threw up the most mud! I emulated the one that made it look easy. Because if he could make it easy here, where everyone else was having a hard time, I figured he would have a hard time where everyone else found it impossible.

I am tired of hearing the excuse, “I don't have lockers.”   Lockers are highly overrated!  Picking a good line and airing down is better than having lockers. Driving off road is not point and shoot. To be done right you need finesse. Yes, I have lockers. No, I rarely turn them on!  I have ARB lockers.  I run open difs until I throw a switch and only then am I locked up!  On the trip last weekend I didn't use my lockers until I was in the mud hole! I did use them more on the trip out, because I had to replace my left front tire with a 31 inch bald tire.

Air down the left front

Air down the right front

Air down the left rear

Air down the right rear

Airing down is not going to 16 psi ---- unless you're driving an
F150 with 235 X 75 15 tires, in which case 16 psi is just about right. I was running 11 psi and could actually have used a little less. 
Yeah, yeah, I know, "but you lose too much ground clearance."  Well, ground clearance be damned. Yeah, I know, "I don't have 33 inch tires.   I only have 31 inch." I am running 33 inch tire's but I am also running 11 psi and I also have a
Dana 60 rear end.  I actually have less ground clearance than a Stock T. J.

1. With reduced ground clearance, pick a better line. 

2. With sufficient TRACTION I can drag the jeep across anything 
(airing down gives you more TRACTION! ) 

3.   Rolling over obstacles -- when you encounter a rock face, the natural  tendency is for the tire to bounce off the rock See the video (to see the video, you will need real player). By airing down you allow the tire to flex and thus roll over the rock and not bounce off of it. You won't need as much momentum to get you over an obstacle because, instead of bouncing around, you'll keep a larger contact patch on the ground (TRACTION).

4. It makes the ride so much SMOOOOOOTHRE!! But only if you air down enough

That is the whole name of the game - TRACTION !!!!  That is what lockers give you - TRACTION! You get your best TRACTION when ALL your tires are on the ground (picking a good line). Airing down helps keep them on the ground. And airing down increases the amount of tire on the ground (TRACTION ).

Now  for most of my trails you can download my GPS track (bread crumb trail) as well as the map of my track. For more info Click Track Info

Full tire pressure 32 PSI   Note 7” of tire side wall and only 3 lugs on the ground. The contact patern is only 6 1/2 long. No sidewall bulge.

Now lets let some air out

At 18 PSI We now have 4 lugs on the ground and 6 1/4 of sidewall. we only lost 3/4” and we now have 8” of tread on the ground.

Now we are down to 11 psi we get some bulge

 11 psi with 5 1/2 inches of tire side wall.  I count 6 lugs on the ground. 11” of tread on the ground!! (TRACTION) and some Bulge on the side wall.

Airing Down Video 6,110 KB MPEG

One of your fellow jeepers was having a terrible time at the beginning of the trail. I asked him if he aired down.  His answer was: yes, to 12 psi. I got my tire gauge and checked his tires.  He had 16 psi.  Using my gauge he aired down to 12 psi. A short while later he came up to me and told me that he was having a much easier time. I suggested that since we are in snow and his tires are very stiff (super swampers) that he might want to air down to 8 pounds.  He declined my suggestion. 

So what should you air down to?  Well, that depends on the size of your tires, the weight of your vehicle and how stiff your side wall is.  I have 33 inch Dunlop Mud Rovers; their side wall is very flexible, which is what I like about these tires, so I run 10 to 11 pounds.
When I had B.F.G. tires with a much stiffer side wall, I was running 8 psi. to get the same squish.

How do you decide how much pressure to run?  With a jeep with 33 X 15 tires at
16 PSI, you won't notice any change, and you may think, “Why air down? It didn't do much.”  For it to work you need to get into the "sweet range" - the area where the tire starts to bulge significantly with each PSI that you drop the pressure.  A good place to start is: take the tire when it is properly  inflated ( by the way, that is not aired up to the maximum psi) and measure from the ground to the edge of the rim.  Now let out the air until you are 75 percent of the original distance, and that is where you start.  You want to see a good amount of side wall flex.  Now try it. Go over an obstacle that you have trouble with.  Let out one pound of pressure and try the obstacle again. Repeat.  Eventually you will see a diminishing return for your drop in pressure.

When you find somebody that is good, ask them what they run for tire pressure when they do a hard core trail. (Don't ask them what they are running for tire pressure now )

Well I am all done ranting and raving for now. Next week I may rant and rave about the judicious use of power.

If you made it this far, thank you for reading my ranting and raving. 
I hope you found it useful. I will be happy to answer any questions or
even go out on a ride.


[Welcome page]

The Odyssey

[Video, Jeeping 101]

[GPS Track info.]


[Odyssey] [Day 8-14] [Day 15 -21] [Day 22 - 28] [Day 29 - 35] [Day 36 - 42] [Day 43 - 49]

[City Match Name] [Name the Folige]


[the shaft] [airing down] [Salsa] [Air Compressor] [Cooking Meatloaf] [Articles in Low-Range]

[City Answers] [Foliage Answers]


[Choke Cherry] [Holy Cross] [Death Valley] [Chili Challenge] [Caballo Mts] [Gila NF Trip] [Titus Canyon]

[Woodpecker Mine]  [Picket Post]  [Box Canyon]