I've seen a whole lot of questions on
OFF-ROAD.COM about what kinds of tire pressures should be
run for off-road use. Nobody seemed to have the right answer.
Perhaps I can shed some light on the subject. Here are the
facts:
General Info
-
If you run a radial tire on your 4x4, the
maximum pressure you can use is 32 p.s.i. cold. When the tire is
running hot, it will rise up to 35 p.s.i.
-
If you run more than 35 p.s.i. in a radial
tire, it will lose its radial characteristics, and will become much
more vulnarable to flats, will lose traction, and become very skaty
on hard packed roads. Also, it will lose most of its flotation
ability on soft sand.
-
About the lowest pressure you can normally use
for off-roading is ten p.s.i., but care must be taken not to push
the vehicle, especially under hard side loads. At this pressure,
flotation in deep sand is excellent. However, steering accuracy
suffers badly and the front end will respond in a sluggish fashion.
Even with power assist, the steering feels heavy, much like your
pump belt is slipping
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The lowest pressure I have ever run is 4
p.s.i., and that was at some sand drags at an event in Rosarito.
The tire looks damn near flat at that pressure, but it works and
you get incredible traction in soft sand or silt. For mud , it's
great.
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Naturally, you have to completely avoid rocks
or any other sharp stuff at this low setting, but I made a dozen
1/8 th mile runs at this setting and my 35 inch BFG All Terrain
tires stayed on the 15 X 7 rims
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At low settings (10 p.s.i. or less), the
stress on the carcass is incredible and prolonged usage will
actually break down the metal wire on the inner lip and cause
seperation of the tire layers in cheaper tires.
-
Radials are the only way to go for serious
off-road use. I have never - REPEAT NEVER - seen a really good
non-radial tire for off-road work.
Tire size is critical when it comes to running
lower pressure. While you can get away with really low pressures in
a 33 or 35 inch tire, the same pressures in a 29 inch tire is
begging for a flat
For all day running in
soft sand (or mud) I would suggest the following guideline:
-
31 inch tires ... 16 to 18 lbs
-
33 inch tires ... 14 to 15 lbs
-
35 inch tires ... 13 to 14 lbs
Anything smaller should not be on your truck in
the first place.
If you're running monster
sized tires, like 44 inch Gumbo Mudders, there's no reason for you
to air down in the first place.
On rocky
terrain, like the Mint 400, I always ran maximum pressure.
On mixed terrain with a mixture of deep sand and
some rocks, 28 p.s.i. cold was always our choice.
For use on slippery hard-packed roads with a lot
of turns, do not run low pressures. It makes for fuzzy steering
accuracy and contributes to excessive body roll if you're pushing
it. Keep it firm and control increases.
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All Terrain tires work better on sand than Mud
Terrain patterns. The M/Ts tend to dig through the sand, rather
than float.
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Steering accuracy is better with the M/Ts in
sand, but you'll spend more time spinning your wheels with the
agressive tread than with the A/Ts.
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On hard-packed dirt roads, the A/Ts hook up
much better than the M/Ts, and you can actually hear them squeal
when you're sliding on adobe surfaces.
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Always run valve caps, especially if you run
at high speeds. When you're on a dry lake bed doing 120 mph, the
small spring on the valve core can lift and let air out. Not a good
thing. Only run valve caps with rubber gaskets in them.
-
If you just want a super comfortable ride, say
for chattery fire roads, try 22 to 24 p.s.i. and it'll smooth the
ride out amazingly well.
Rick/Somewhere in
Baja
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