Air down for non technical dirt roads?

[Glen]

Don't have a bunch of experience yet, but I've been playing around lately in the local desert with a combination of airing down slightly & softening the Fox 2.0 shocks with the adjuster dial. So far, I seem to get a decent ride on anything but heavy washboard by taking 10 lbs. out of the tires and going down 2-3 notches on the shocks.

I've got a 2011 E350 EB that weighs right around 9,200 lbs. (I still don't have solar or any interior cabinet, etc.)

[geoffff]

I always air down if I'm going to spend the day driving off-pavement roads, even if they're easy. The ride is so much nicer that way. I drop usually to 2/3 pressure.


-- Geoff

[geoffff]

I calculated my tire inflation from the Load and Inflation Tables. All the tire manufacturers publish these, and their numbers all match - regardless of brand. Only the tire size matters. Here is one from Goodyear:

http://octopup.org/img/car/tires/Goo...ruck-Tires.pdf

I weighed each corner of my van, while it was heavily loaded, and got the following values:

• Front L,R (lbs): 2100, 1950
• Rear L,R (lbs): 2800, 2650

When I look up my tire size (LT305/70R16) in the table, I see that for 65 MPH highway driving, I should be able to run 35 PSI front and 50 PSI rear. (I used to run 285/75R16, so I've highlighted those values as well.)

I usually round up to 40 PSI front and 55 PSI rear, just to have an extra margin of safety.

I also look at the tire temperature values from my TPMS. All four tires should show roughly the same temperature, even with different pressures - if they each have the correct pressure for their load.

On dirt logging roads, I run 25 PSI front, 35 PSI rear.

In deep soft sand, I go down to as low as 15 PSI.

-- Geoff

[Otter]

Thanks for posting these guidelines. I just located the table for my BFG’s. Apparently, I’m running my tires way too high. Can someone help me understand why these numbers are so different from from the recommended psi’s printed on the tag inside the drivers side door? What in the heck circumstances are those numbers referring to?
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[geoffff]

Originally Posted by Otter

Thanks for posting these guidelines. I just located the table for my BFG’s. Apparently, I’m running my tires way too high. Can someone help me understand why these numbers are so different from from the recommended psi’s printed on the tag inside the drivers side door? What in the heck circumstances are those numbers referring to?
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Carrying maximum load? Smaller tires?

[basssears]

Thanks for everyone's input, good stuff as always.


I think I can go to the dump and just get my overall van weighed, how do people weigh each corner?


-- Bass

[simplesez]

Trucker scales can weigh each corner.

[WhitH]

You absolutely want to air down for that long of a stretch even if there is a chance for washboards. It makes a huge difference. I go down to that 40-45 range if I’m spending a day off pavement even if it’s just logging roads. The more well traveled and straighter the road the more likely you’ll see some washboard as folks will be moving faster.

[BenJJ]

I would definitely air down in those situations. I usually run 50/55 on pavement and air down to 25 off road.

[Glen]

I took a friend who has never been "off-roading" out with me the last time I played in the desert with the van. He asked me a question that I've never really given much thought to. He asked me what causes the washboard. I've just always accepted that they are part of the experience.

I don't really know exactly how/why they are formed. I do know that no matter how many times the camp owner at our place in Baja grades the dirt road leading into our camp from the highway, the washboards return fairly quickly.