Good point, i just got a small compressor for the car to go along on my hunting and camping trips. I will try it, just seemed to be to much headache.
I agree with Paul on this. Finding the "sweet spot" to air down for a given situation is like day and night when driving off road. My question really had to do with the fact I've never driven a rig with passenger car tires seriously off road before. I'm not sure what kind of sidewall damage to expect and wanted to get a feel for how others are wheeling their rigs.
Try airing down in your garage first. Make a chalk mark in front and behind where the tire tread meets the floor at various pressures and you will see just how much larger the contact patch actually gets. Here are some pics of a typical tire being aired down from 30 psi to 15 psi and finally 7 psi. Remember that less air also means the tread is much more malleable and able to conform to uneven surfaces like on a rocky ledge.
With an Xterra loaded with people, tools, gear, water, food, etc., for an offroad outing we probably tip the scales somewhere in the 6,000-6,5000 pound mark. On those washboards Paul was talking about you will be blown away how your rig handles running 20-24 psi in your tires. For speeds under 20 miles an hour for our stock 265 or even 285 tires I would not recommend airing down to less than 14-16 psi. I've gone down to 10 or 12 with 31's on my Rubicon but it is a much lighter vehicle. Now that I run 35's on beadlocks I've occasionally taken them down to 4psi with no problems.
Of course the down side to airing down is airing up. I have an old QuickAir II that will handle the job on the Xterra in about 4-6 minutes per tire. Make sure whatever electric compressor you end up getting has a duty cycle that will allow it to handle you tasks without having to wait for the unit to cool down. Something like the Vivair 450C at $469.99, is a continuous duty compressor and will air a 33" tire from 15-30 psi in about 3-1/2 minutes while only drawing 19 amps off your battery. In contrast, the Harbor Freight Central Pneumatic 66399 compressor for $74.99 ($59.99 on sale) claims to perform about the same but list no duty cycle in it's manual and draws a whopping
30 amps of power. Finally there's something like the Harbor Freight 4077 12 volt, 250 PSI Compact Compressor for $11 or less that plugs into you cigar lighter outlet and will probably have a melt down after a couple of uses. Do not consider any compressor that is not hardwired or clamped directly to the battery.
