B190 Enthusiasts

Does anyone hear have experience with airing down their tires for taking the van off road?

I want to take my 1990 b-190 to the Racetrack Playa in Death Valley, which is along a 20 mile rutted dirt road that is known for blowing people's tires.

From what I've read airing down the tires is a good way to make the drive a lot smoother and save your tires from getting damaged at the same time.

So far all of the tips I've read focus on tires that are normally inflated to 45-50psi, but our rear tires are supposed to be inflated to 80psi. How low can they safely be taken assuming you're driving max 15mph along the trail? I will be bringing along an air compressor to be able to air back up after I get back to normal roads.

Its been my experience in Alaska where there is lots of the kinda roads you described that tires problems are directly related to speed traveled, assuming the tires are decent to begin with

I suppose reducing the pressure some when maintaining a slower speed wouldn't hurt but I don't think I'd reduce the rear from 80 all the way down to 45-50..

Keep in mind, our rigs carry a front end weight of about 3600 total and 5600 on the rear (I've weighed mine a few times front & rear) . The max carry cap of these tires is around 3000lbs each and thats why the air pressure of 80psi...based on average highway speeds

Another thing to consider is that with reduced tire pressures and the weight we have up high in our rigs you can then expect the rig to feel even more top-heavy than it normally would due to lack of support of the tires with reduced pressures

I think I would try that road with normal tire pressures, keep your speed at that 15mph to start with and if that doesn't seem to work perhaps drop the rear pressure by 20psi.

Most of those little air pumps won't inflate to 80 psi....

I found the following document very interesting. It gives the standard specs for safe tire loading that are based on highway speeds, *and* gives information on how that can be adjusted for lower speeds:

http://www.goodyear.com/truck/pdf/edb_loads.pdf

So, for example, with the tires on my 1990 B190 - LT235/85r16

Page 7 gives the standard cold pressure necessary to carry the weight. With Alaskan's values of 3600 front and 5600 rear we get

1800lbs/tire front - gives 46psi front, and
2800lbs/tire rear - gives 75psi rear

Adding more pressure (up to the tire max) means you can carry more weight. Also keep in mind the weight should be based off a loaded vehicle including the weight of any passengers.

Page 2 gives adjustments you can make for traveling at a different speeds. According to that table the normal load ratings cover driving 56-65mph. If you go faster you would want to increase the psi, and if you go slower you could carry a heavier load at the same psi or reduce pressure.

According to page 2, if I'm driving 15-25mph, the load carrying capability of the tires goes up by 32%. With the increased capacity due to a lower speed, page 7 now gives these values:

1800lbs/tire front/1.32 = 1364 lbs <= 35psi front
2800/tire rear/1.32 = 2121lbs = 50 psi rear

Hopefully other people find this interesting/useful. If you notice any errors in my understanding (or math) please let me know.

Great info... thanks-a-lot

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