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Old 09-07-2009, 10:59 PM   #1
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Question, Airing Down for off road?????

Hello all,

Our family had a great Labor Day excursion today and I was trying to figure out which pressure to run in my rubber for off road driving. We were not rock crawling, no will we be anytime soon in our van, but we do go off road quite allot and figuring this out would be very helpful.

So it got me wondering what other SMB owners run...

I'm all ears & thanks in advance!
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Old 09-07-2009, 11:04 PM   #2
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Re: Question, Airing Down for off road?????

Quote:
Originally Posted by AdventureRider
Hello all,

Our family had a great Labor Day excursion today and I was trying to figure out which pressure to run in my rubber for off road driving. We were not rock crawling, no will we be anytime soon in our van, but we do go off road quite allot and figuring this out would be very helpful.

So it got me wondering what other SMB owners run...

I'm all ears & thanks in advance!
I run E rated tires and generally drop the pressure down to 40psi when I head off road. Like you, no rock crawling for me. Usually just a lot of washboard. The lower pressure really helps. But it is a commitment because it takes nearly an hour to air back up, even with the onboard air. If I'm going on and off road throughout the day, I won't bother to air down.
R
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Old 09-08-2009, 01:26 AM   #3
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Re: Question, Airing Down for off road?????

hey adventurerider - from my "research" a rule of thumb is drop air to no less than 1/2 what you normally run on the street for dirt, sand, washboard off-road conditions. The you just have to go from there because there are so many variables that affect what you should do.

EM - what psi do you normally run on the street - ? And 1 hour to fill 4 tires is waaaay too long for me.
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Old 09-08-2009, 08:29 AM   #4
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Re: Question, Airing Down for off road?????

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EM - what psi do you normally run on the street - ? And 1 hour to fill 4 tires is waaaay too long for me.
I usually run 70-75psi on the street. If I could air back up a bit faster, I'd probably go down to 30-35psi when off-road.
R
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Old 09-08-2009, 09:18 AM   #5
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Re: Question, Airing Down for off road?????

I take my BFG's from 50psi (normal for the 315's) down to 30.

With the onboard extreme air it takes about 5 minutes each to bring them back up to street pressure.
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Old 09-08-2009, 09:59 AM   #6
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Re: Question, Airing Down for off road?????

I have the same questions about airing down with our new SMB, 285-75 R16 w. D rated tires

On my old 4wd f250 which ran @ 50 psi on the road with 265-70-R16 D rated I would drop to 25 for bad dirt roads, and stay under 25mph.

I would drop as low as 15 psi for the sand.

I usually have a small 40 cf LP SCUBA tank for airing back up, takes less than 5 minutes to get them all back to 50 psi.

Im guessing the SMB is alot heavier, Ill probably start by seeing how 30 psi feels.
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Old 09-08-2009, 10:02 AM   #7
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Re: Question, Airing Down for off road?????

I dont have a sportsmobile yet, however ive spent a lot of time in baja in various rigs and know that if your going to be hitting it up on washboards, or rough fire road type terrain, you gotta drop that pressure down to at least 20 psi, or even 15 if there's any sand involved. Why people run soo much air in their tires is beyond me, cause all its going to do is start breaking things. Less air in the tires will make for such a smooth ride, wont stress out suspension parts, and make it ride like a caddy. Youll also find that your a lot less prone to spinning tires and have a lot more grip with less air. It also depends on how far your traveling, if your going to mix any pavement time in, time to air up, availability of air wether or not its on board or gas station air.

I have also left the pressure at 15-20psi for weeks on end while in baja frequently traveling up to 60+ mph on washboard and have yet to have a problem. However due to the amount of weight that these rigs see, i probably would keep the rear 5-10 psi higher than the front just so u dont have an issue with separating a bead.


Quote:
Originally Posted by AdventureRider
Hello all,

Our family had a great Labor Day excursion today and I was trying to figure out which pressure to run in my rubber for off road driving. We were not rock crawling, no will we be anytime soon in our van, but we do go off road quite allot and figuring this out would be very helpful.

So it got me wondering what other SMB owners run...

I'm all ears & thanks in advance!
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Old 09-08-2009, 10:44 AM   #8
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Re: Question, Airing Down for off road?????

I'm pretty sure running at low pressure causes heat buildup and the additional flex both are major contributors to tread separation and/or blowout when you later drive at highway speeds.

I also believe that a blowout may cause roll over in a van.

I suspect this is why people don't air down.

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Old 09-08-2009, 12:00 PM   #9
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Re: Question, Airing Down for off road?????

Goodyear's web site has a pdf downloadable version of their off-road tire manual. In it they state that it's okay to reduce pressure for better traction IF the tire will be running in sand or soft dirt that actually cradles the tire, providing support to help avoid, inter alia, sidewall breakdown. They say that it's NOT a good idea to reduce pressure for any extended period of time, or at high speeds, if the tire will be running on a hard surface and the tire does not sink into the surface.
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Old 09-08-2009, 12:41 PM   #10
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Re: Question, Airing Down for off road?????

Quote:
Originally Posted by JMan
I dont have a sportsmobile yet, however ive spent a lot of time in baja in various rigs and know that if your going to be hitting it up on washboards, or rough fire road type terrain, you gotta drop that pressure down to at least 20 psi, or even 15 if there's any sand involved. Why people run soo much air in their tires is beyond me, cause all its going to do is start breaking things. Less air in the tires will make for such a smooth ride, wont stress out suspension parts, and make it ride like a caddy. Youll also find that your a lot less prone to spinning tires and have a lot more grip with less air. It also depends on how far your traveling, if your going to mix any pavement time in, time to air up, availability of air wether or not its on board or gas station air.

I have also left the pressure at 15-20psi for weeks on end while in baja frequently traveling up to 60+ mph on washboard and have yet to have a problem. However due to the amount of weight that these rigs see, i probably would keep the rear 5-10 psi higher than the front just so u dont have an issue with separating a bead.
That may be enough pressure for whatever vehicle you have, but it sounds too low for a heavy van. When I took an off-road course the instructors were all Jeep based, and they wanted to air down to 15-20 psi. Of course, they were only running 35 max on the street. When I told them that I'm starting at 80 psi and wouldn't air down that far their response was 'Never heard of tires with that much pressure.' So, I aired down to 40psi and go the same sidewall bulge they had at 15-20psi and everyone was happy.

Airing down to 1/2 your road pressure is a good starting point for off road. Less for heavy sand, but air back up before driving at speed.

And it can take a long time to put high pressures back into the tires. To double the pressure takes 4 times the air. So, our higher pressure tires take much longer to air up than lower pressure tires.

Mike
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