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Old 08-23-2018, 01:43 PM   #1
Join Date: Aug 2015
Location: Englewood, Co.
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Airing down question

So for years I have always aired down my jeeps and buggys' before going offroad. This past weekend I took my SMB up a nasty rocky fire road but was not sure if I should air down and if so how much. I have never driven anything this heavy off road so I just crawled it. Looking for some advice.
It is a 2003 E350 SMB EB 4x4. V10, chateau roof, Agile offroad kit, and running 285 E rated BFG AT2's. gotta weigh in @ 5 tons.


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Old 08-23-2018, 03:41 PM   #2
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I have my Staun tire deflators set to drop my pressure down to 35 when I get ready to set off on the dirt. Sometimes I will a little more air in the tires if its just a short dirt section or mild fireroad. I go as low as 20-25 for deep sand. My van does not have a heavy build out like an SMB so probably close to 8000 lbs currently.

2012 E350 RB XLT Wagon, Agile 4x4, SMB penthouse
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Old 08-23-2018, 03:54 PM   #3
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I've gone down to as little as 20psi with 285-16 BFG A/T's if I recall correctly.

I look for 'foot print size and sidewall bulge' more than tire pressure, as those two are a function of vehicle weight, pressure, and tire construction. I shoot for about 1/3rd reduction in sidewall height, which in turn makes the tread footprint larger.

More than that, and I get concerned I'll pinch a sidewall of break a (cast aluminum) wheel if I smack a ledge or sharp rock.

In the sand, you can go 'flatter and fatter' than that if needed, you just have to keep the tire from popping the bead.
1995 E350 7.3 Diesel, 4x4 high roof camper, UJOR 4" lift
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Old 08-23-2018, 04:40 PM   #4
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Touch the sidewall...if it is "hot" (like close to burning your hand), you're going too fast or running too little air for the speed/weight. Get in the habit of touching your tires after running on the freeway or off road - you'll get a sense for when it it too hot. Tire will be internally damaged due to thermal or mechanical stress for under pressure issues.

You can also blow a bead and be more! ( Yes more) suspectible to sidewall punctures if your down too much. Wish I had some better guidelines (like actual temps or psi)...

Also, it is not sidewall bulge that matters when airing down - in fact, you really don't want to have much sidewall contact as it is not designed for it (sand is a different story) the tire footprint lengths and this is what adds traction.

All that being said, I'd start with 30-35psi...and go down from there. (I run 10-12 on my jeep and 18-28 psi on my sprinter van that is sitting on 35s).
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Old 08-23-2018, 06:40 PM   #5
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I usually drop to 30 front and 35 rear on gravel roads. Seems to ride and drive just fine at those pressures. Running 265/75 16 KO2s.
Read detailed trip reports, see photos and videos on my travel blog,
Current van: 2002 Ford E350 extended body camper with Colorado Camper Van pop top and Agile Offroad 4WD conversion.
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Old 08-23-2018, 08:54 PM   #6
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'..nasty rocky road/s..'- I crawl along smooth and easy, picking the best line, and, I haven't had to air down yet.
Sand and powdered dirt, I got nothing.
Backcountry rocky roads have been our main haunts and if anything it's when to fire up the lockers; maybe we'll learn a lesson the hard way, but so far our 285/75 - 16 bfg at ko's appear to not know the difference.
Hat's off to Agile RIP by the way...
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Old 08-23-2018, 09:13 PM   #7
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Depending on the sharpness of the gravel on gravel will also see less punctures. Northern Baja as an example—airing down will save you punctures. I speak from experience...
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Old 08-23-2018, 09:45 PM   #8
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We have EB350 with cruiser top and V10 which looks to be similar in size and weight to yours. We typically drop our pressure to 50 in the rear and 40-45 in the front. This seems to work well for us.
2012 E350 EB50 V10 Cruiser Top
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Old 08-23-2018, 11:25 PM   #9
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Been discussed here a few times, this is a good thread:

I’ll do as low as 25 offroad, depending on speed and conditions. Dropped them down to 10 to drive out of a dune in Baja. But I wouldn’t go very far with less than 25.

This is 15psi in my old 285s:
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Old 08-24-2018, 07:34 AM   #10
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‘...this is a good thread:...’
Thanks for the Thread Link RPA, solid info in there.

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