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Cypress
Elite Nomad
Posts: 7641
Registered: 3-12-2006
Location: on the bayou
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Mood: undecided
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Been thru a mile or two of rough roads at work and at leisure. Wouldn't
recommend zipping over miles of washboard with low pressure tires, sidewalls are thin and easy to puncture.  Low pressure is great for sand, mud, snow, etc. Washboard is caused by the harmonic oscillation of tires on the road
surface. You just have to adjust your speed to the washboard and be in harmony with the oscillations. A smooth ride will be your
reward.
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Barry A.
Select Nomad
Posts: 10007
Registered: 11-30-2003
Location: Redding, Northern CA
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Mood: optimistic
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It has been my experience that "high speed coupled with low pressure" is not good-------it is a good way to pinch the tire against the rim when
hitting rocks, thus causing tire failure, as well as exposing the sidewalls to rock damage, as has already been pointed out.
Slower speed (much slower than what you are talking about) and lower pressure IS good, and is usually the way I drive rough roads, the actual pressure
depending on how heavy my rig is----heavy = higher pressure.
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Shimmer
Junior Nomad
Posts: 69
Registered: 11-29-2005
Location: Todos Santo BCS
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Mood: In the Question
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I drive a '99 3/4 ton Suburban around the roads in and out of Todos Santos. I found that 25lbs saves the rig alot of ware... even over 30 lbs, which
I used to run before I made my last discovery. As mentioned above the weight is the factor. I was surprised to find the difference in such a few
pounds, but it is noticeable. I'm going to try working down to 20 to see which is the best for my weight.
S
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Barry A.
Select Nomad
Posts: 10007
Registered: 11-30-2003
Location: Redding, Northern CA
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Mood: optimistic
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Shimmer----------
IMHO 25 is perfect if you don't carry a lot of stuff and drive at reasonable speeds-------I would not go lower unless driving really slowly, or you
have super big tires and/or are in mostly sand.
For over 13 years of driving the dirt roads in the California desert, our fleet of 10 lightly-loaded full size 4x4 pickups used 10:00 x 15 tires, load
range C, on 8" wide rims, and ran them at 26 lbs. and seldom had any problems, and they wore great, often getting over 30K miles before discarding.
We arrived at that tire pressure after much trial and error.
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ClimbBaja
Newbie
Posts: 1
Registered: 7-6-2007
Location: San Diego/OB
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There are some variables missing from your post, esp, the brand, size, and load range of your tires. Also the weight of cargo and/or camper.
Off hand, I'd say 22 to 25 psi would give you a significantly softer ride. That should also improve braking distance, provide better traction and
steering control as the "footprint" or "contact patch" of the tire increases on the dirt.
As you air down, you should be looking for a smooth bulge of the sidewall. Some tires have stiff sidwall characteristics which don't show a
progressive bulging, but rather do almost nothing until they begin to fold or crease. Crease = bad.
A smoothly bulging sidewall can probably be aired down to 12 psi for running sand (no rocks). 8 to 10 psi briefly to get unstuck. Running pressure in
these low numbers will require you to carry a souce of compressed air.
[Edited on 7-7-2007 by ClimbBaja]
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David K
Honored Nomad
Posts: 64835
Registered: 8-30-2002
Location: San Diego County
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Mood: Have Baja Fever
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ClimbBaja is right on...
I have noticed that BFG All Terrain T/A's do not buldge very well and are thus not the best sand tire. Aggressive (mud/ snow) treads are also poor
sand tires... In fact, the smoother the tire, the better, in sand.
In the 'old days' Armstrong Hi-Way floatation tires (sold by Dick Cepek) were great... they resembled aircraft tires.
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Barry A.
Select Nomad
Posts: 10007
Registered: 11-30-2003
Location: Redding, Northern CA
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Mood: optimistic
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-------------and in the even "older days" David, we used aircraft tires with their straight grooves, and they also worked very well in the soft sand,
as I know you know. 
Things certainly have changed over the years. I still am a fan of BFG-AT all-terraigns, and have them on all 3 of my 4x4's.
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TMW
Select Nomad
Posts: 10659
Registered: 9-1-2003
Location: Bakersfield, CA
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In the 2004 SF250 race Mike Doherty broke an axle in his class 8 truck. With one wheel drive he was getting stuck in the sand. We aired his 35x12.50
BFG tires down to 5 lbs (all 4) and he went thru the sand with no problem, running race speed, until near Matomi and hwy 5 he had to stop behind a
stuck buggy and he too get stuck and timed out. At 5 lbs you could hardly tell they were low on air. Vanderway ran the entire Baja 2000 on 24psi in
his class 8.
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