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Discussion Starter #1 (Edited)
We are embarking on an off road only moose hunting trip here in Alaska in our 406 that will involve hard ground, soft ground and lots of mud. We have michelin XM37 tires in 12.5 width tubeless. What does anyone think is the lowest air pressure I can run without much chance of the tire debeading. We are on stock 11x20 drum brake wheels. thanks for any advice we will be about 50 miles each way off road with some big climbs and river crossings. We will be trailering the mog to the start and finish.
 

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'78 Mog 416.141 DoKa
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How stiff are the sidewalls ? A lot of those tires were made in various configurations and the sidewall stiffness varies.

The higher the load rating, the more you can air down. SOME of the real stiff side wall tires can be easily run on a 406 with almost no air if you're empty (by Mog standards).
 

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'78 Mog 416.141 DoKa
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The higher the load rating, the more you can air down. SOME of the real stiff side wall tires can be easily run on a 406 with almost no air if you're empty (by Mog standards).
Of course, the variables of off highway terrain are almost endless. While you may be able to run a tire with no (or very little) air on a hard surface successfully, in very soft or loose ground, or ground covered with tree litter, you may get foreign matter between the rim and tire which could lead to a leak or de-bead.

There is no definitive answer to your question. You can not look to the OEM of the tire for guidance since this is outside the conditions the tires were designed to operate under. For example, the Conti MPT-80's I use are spec'ed to a minimum pressure of 1.1 bar under certain load and terrain conditions. This is not specified as a MINIMUM, that's just as low as they spec. I have routinely run them at much less then this at low speed and light load.

If I were you, I would probably start out at 50% of the on-road pressure spec, see how the profile looked and adjust from there (assuming you are not heavily loaded). Those tires are not wide enough to give good flotation in boggy conditions so, as long as the tire can conform to the terrain obstacles well (rocks, logs, ect) at a given pressure, that's probably good enough. Lower then that will just have the potential to cause problems.

Besides, with the tractor v-bar tread, you're not going to change the footprint with pressure very much, just the conformity of the sidewalls.
 

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Non MB 1975 Volvo C304, 1958 Kramer U540, 1959 unimog Westfalia 411
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I have run various tires on my 406 as low as 6 psi. I run 425/70 XM 27 that's 16.5 inches wide on 13x20 wheel and 10/12psi works good for the trails with stretches of cobble/ boulders that dominate miles of the trip. As stated previous with a new setup I would watch the bead area for debris running anything under 15psi. Should be interesting out there after the breakup from last year. Happy Trails I am trying the jet boat approach this year to unchartered waters.
 

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Discussion Starter #5
I will be going in with about 600Lbs in the bed and it has a heavy rear plate and hopefully return with an additional 1000lbs of moose meat. We were climbing some short steep hills in glacial silt sand to check out the lockers and felt a lower air pressure might have helped but I don't want to risk a debead on the trip. The tires are rated for max pressure of 27psi so I might start at about 18 and go from there. Next year I would like to have some higher floatation tires.
 

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2007 SL550, 1996 E300 Diesel, 1959 220SE, 1965 Unimog 404.115-Sold
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Had you thought about installing tubes? Then you would not have the problem of breaking the bead seal. Maybe that is not possible with those tires?
 

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guude,

the tube valves like to rip off when pressure is low and the tire turns on the rim.

gut mog! justus.
 
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