Air Down Or Not To Air Down?

[Steve_t647]

Right you want more traction and understand bigger tyres alone will not give it are there other options? Air Down Or Not To Air Down? (not for experts)

This is the question that has plagued four-wheelers for ages. For serious off-roading, it is a definite improvement over fully-aired rubber. However, once you are back on the road, aired down tires can be loud, wear unevenly and be right down dangerous. The risk of a tire coming off of it's bead increases with speed and with less internal pressure, the risk multiplies greatly. Therefore, it is essential to air back up when you are done four-wheeling, factor this time into your return trip and a stop at the gge to re-check them.

If you use a tire such as the Super Swamper that uses very large side lugs, it is most effective when aired down to 8 psi or lower. This allows the tire to conform to the terrain. Large heavy tires with large lugs dig into the terrain much better if they can get a larger "footprint" into what they are running on. This is attained easily with a drop in pressure.
Now comes the next big question. How low can I go?

This is a big factor that is based on:

A. What terrain are you tackling?
B. Which tires and rims are you using?
C. What size/weight is your rig?

SNOW SAND and grqavel: In snow, specifically snow that is packed and wet, you can air down safely to 12psi and if you struggle down to 8 psi. This will allow the footprint to expand and allow a great grip into the slippery terrain. With snow being slippery and dense, the tires will conform and help to compact it. This will also help others following behind you as a packed powder will be easier to traverse than one that is loose.

MUD: A lot of people think airing down in mud is a bad thing. Since tall thin tires tend to do best in mud, big sidewall lugs don't always help too much. This is your call but I wouldn't go below 20 psi here unless you have the tread pattern for it.

ROCK: This is essential. Huge sidelugs aired down can engulf rocks and let your rig move effortlessly over them. One lug can often catch the sides of a rock and pull you to safety. Some people prefer many small lugs here but I prefer fewer larger lugs aired down to 5-8 psi as they can usually hold you like to other combination and since you are traversing at such slow speeds, your bead should remain intact.

I hope this helps you all in your airing down practices and tyre options these are not for every 4wd or type of tyre experimentation is recommended.

[lincooln]

I have found that in my Suzuki, that 20psi is much the same as 30psi, So i like 15 or so in the mud. Two things that affect mine though is 1:It is a Vitara so is light compared to most 4wd's. 2:I have tubes too, so this allows lesser pressure.

Cheers
Lincoln

[skid]

80 series cruiser, running 33" muds on 15 x 8.5 rims, 2500kg

tend to do forestry tracks, rutted tracks in clay/rock/mud, rivers and sandy beaches.

have always run my tyres at 25psi on the road which most people cringe at, but I find it comfortable and I run at 18psi off road, but it seems a lot of the time lately I have been running them at 18psi all the time on and off road and it handles fine at that pressure all the time.

have got the occasional bit of mud forced into rim, but never had a bead pop off.

[Ralfie]

with or without tubes..........??

surprisingly they do make a difference as to how low you can go.......

[albundy]

have got the occasional bit of mud forced into rim, but never had a bead pop off.

Your not driving hard enough Skiddy. But, sheeet, you sure know how to drown a toymota.
Al

[rokhound]

I run at 40 psi on road and 5-7psi off. That is why i have 15.5" wide tyres on 8" wide rims. Have not lost one yet, but I guess it is only a matter of time

[meatc]

lately I have been running them at 18psi all the time on and off road and it handles fine at that pressure all the time.

Tyre pressure on the road when hot will be about the same regardless of starting pressure. They heat up more hence equal tyre pressure. The extra heat will make the tyres fail prematurely. Have you noticed that at 18psi your truck feels soft to drive for the first few kays?

The reason race cars alter starting pressure is to adjust the heat in the tyres and therefore the grip and wear.

[jaslux]

Another point is the construction of your tyre whether bias or radial.

Bias ply tyres generally have thicker/stiffer sidewalls and hold their shape alot better when aired down, compared to radials which tend to squat/balloon out. Bias plys are also less likely to get sidewall damage because of their construction, which is a danger when aired down in some situations.

Just my 2c

[Steve_t647]

This is a discussion document and pretty generic, obviously bead locks secindair inner bead locks tubes and weight of car and obviously tyre construction (something I missed). Some 4wd tyres have thicker stronger beads, hard to fit and remove but they are harder to have spin on a rim also.

My pressures are mostly safe for everyone One other thing I missed is the more serious you are and the better setup the 4wd the more important having a matching size spare actually is.

A lunchbox locker with differing size tyres could be ugly.

[red-devil]

i run the VX tires at 40 psi on the road and 15 offroad

there 35/12.5/15 mtr wranlgers.

i run them low for a nice ride so lili and me dont get bouced around

[Shane]

I run as low as 10psi (rear)12psi (front) if I know the terrain,the differance in grip from say 18psi is quite alot(nice ride also).if the tracks rutted and I dont wont to lose too much diff clearance I run 16-18psi.I've never popped a tyre off yate on a 2.5Ton POS.(no tubes)I do get shit in the beads though,part of that is the shity BFG rim protector that help to push the tyre of the bead,has been deleted on the new BFG.

Tyres are 35/12.5/15 BFG's on 8" rims,vehicle is LWB Safari

Shane

[Beer_Cruiser]

I run the 40 with 35x14 1/2 Pitbulls. Last time I had a look they where at between 6 and 7 psi

[its_that_guy2]

80 series cruiser, running 33" muds on 15 x 8.5 rims, 2500kg

tend to do forestry tracks, rutted tracks in clay/rock/mud, rivers and sandy beaches.

have always run my tyres at 25psi on the road which most people cringe at, but I find it comfortable and I run at 18psi off road, but it seems a lot of the time lately I have been running them at 18psi all the time on and off road and it handles fine at that pressure all the time.

have got the occasional bit of mud forced into rim, but never had a bead pop off.

lol never ????
i seem to recall turning up to rallywoods and sitting there for an hour or two with another member waiting for you to come back from galavanting around in jafa;s truck .. and just glancing over to see not one but 2 off the bead ....

[taz01]

id like your thoughts here .....running 37 mtr aired down to 8 to 10psi worked great on rock however mud they wouldnt clear, would going up to 15psi work better ? keep in mind their on a safari with no horsepower and weighs 3ton............

[skid]

id like your thoughts here .....running 37 mtr aired down to 8 to 10psi worked great on rock however mud they wouldnt clear, would going up to 15psi work better ? keep in mind their on a safari with no horsepower and weighs 3ton............

wheelspin clears mud Taz

nissan V8 would do it for ya me thinks

[taz01]

id like your thoughts here .....running 37 mtr aired down to 8 to 10psi worked great on rock however mud they wouldnt clear, would going up to 15psi work better ? keep in mind their on a safari with no horsepower and weighs 3ton............

wheelspin clears mud Taz

nissan V8 would do it for ya me thinks

not the answer im looking for skiddy....................

[NJV6]

running 37 mtr ...snip.... however mud they wouldnt clear,

Answered your own question - its the tyre, they are not a mud tyre. More a cross between an all terrain and a Mud terrain. M in MT/R doesn't stand for Mud. Good on rock however.

[new2zukes]

well i have always let my tires down to as low as posible for mud and that is the main part of my wheeling. first off i had a suzuki samurai with 29x 7.5 simex tires them let down to 5psi worked well worked even better when they were put down to 2 or 3 psi but i started to spin tubes alot. as for my new truck it is about the same weight as a zuke but is running 35x13.5 r15 mudzillas on 8inch rims (beadlocks) i run them at 2psi in the mud and they bite really well, they are a very wide tire and work best in ruts due to the great sidewall grip. the tires dont bag that much when at that low pressure but they sure do bite.

[Steve_t647]

In a light 4wd like a Suzuki it may not work this way as they skip over the top, what I have found with mud is if you lower your pressures it has a wider footprint that sucks up more loose mud, and by the time you have you have spun the wheels enough to find grip you just dug a wider longer channel you cannot get out of.

With harder pressure I find the tyres clear a little better but they dig a narrower shorter channel in the mud to the grip under it that allows you to get out of the "flat spot" when you get grip.

Now climbing out of the hole on the other side well that could do with lower pressures as there is grip.

You also need a tyre that will clear mud, the more open the tread pattern the better. Remember if you have big side lugs (Like Simex) these will benefit from lower pressures.

Tyre size helps with clearance to the bottom of the diff a suzuki on 31's is the same clearance as a hilux on 33's this is the same as a Safari on 35's

[Ralfie]

In a light 4wd like a Suzuki it may not work this way as they skip over the top, what I have found with mud is if you lower your pressures it has a wider footprint that sucks up more loose mud, and by the time you have you have spun the wheels enough to find grip you just dug a wider longer channel you cannot get out of.

Are you sure the tyre is wider at lower pressures?
I recall reading in the 4WD mag a few months back that tyres at lower pressures do not get wider at lower pressures but the footprint gets longer. They did a simple test to show the footprint at various pressures and they weren't any wider.

[albundy]

Are you sure the tyre is wider at lower pressures?

Yep, my silverstones gave a wider footprint at 8psi then they did at 40psi. All you have to do is look at the traclk it makes at both psi settings.
Al