Saline Preservation Association

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mcbane

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Posts: 5
 #1 
The tires are 42 " x 14.5" wide so the contact area is a bit bigger and you need a bit less pressure than you would with a smaller tire.  The truck owner's manual calls for only 45 psi with this tire size and at that pressure there is barely any visible sidewall deflection.  I'm getting pretty even tread wear at that pressure so I havent experimented running higher pressures.
Oobleck

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Posts: 39
 #2 
Thanks McB, that was very helpful. But I have a question: If you have a 12,000 lb rig, why are you only running 45 on pavement? I get WAY better mileage when I air up to 80 psi (the max recommended for my tires) on blacktop. I would also think with that weight you would wear out the edges much quicker running soft on pavement. Just curious.
mcbane

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Posts: 5
 #3 
My $0.02:

Tire pressure recommendations in references such as the yokohama guide are the pressure you want for a given load to be able to run at highway speeds.  If you drive at less than 65 mph less heat is generated so you can afford to go below the officially recommended pressure at lower speeds. 

My 12,000 truck runs at 45 psi on the highway but I air down to 30 psi for the washboard.  After airing down I drive at the smoothest running speed, which is usually somewhere close to 20 mph.

In close to 20 years of trips into the desert, my experience with flats is that the leading causes of failure are:
1) badly worn tires.  I have never seen a flat on a quality tire that had 3/8" + tread remaining
2a) extraordinarily cheap tires like you find on rentals and sometimes see as low dollar OEM equipment.  Every time I camp with someone driving a rental, they get one or more flats - no exceptions.  It could be that people just thrash rentals but I am more inclined to blame this on junk tires.
2b) extraordinarily cheap tires like you see on trailers.
3) driving too fast.  Even if you arent fishtailing in the corners, trying to drive too fast means more tire spinning as you go over the bumps and that is a good way to drive a sharp rock into the tread.

I have NEVER had a flat on a high quality tire running at lowered PSI and driven at sane speeds.


 
sandapanda

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Posts: 3
 #4 
tire pressure chosen depends on what kind of tire you are running - I assume in a vehicle this heavy its E rated - look at tire manufacturers website, there are usually charts for weight/tire pressure/load rating relationships.

Here is one for Toyo http://toyotires.com/tire-care-safety/load-inflation-tables it works pretty good for all tire brands
CharlieC

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Posts: 4
 #5 
With that much weight in your rig, I wouldn't go below about 45 in the back.  Up front, you could go lower, maybe 30.  Check out the powerstroke.org forum, you can probably find more specific info over there.
Oobleck

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Posts: 39
 #6 
Thanks Stuck. That's a sweet rig you've got there, but we're talking a serious Redneck Stretch Limo here:

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Oobleck

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Posts: 39
 #7 
Quote:
Even if you could air down for a soft cushy ride speed will kill your camper.


Yep, the last time I came into Saline, the cupboards emptied onto the floor and I lost one of the hydraulic camper jacks (later retrieved by someone coming in Bat Cave Rd - and I was going slow :-)
XPBC

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Posts: 189
 #8 
I run my Jeep on Goodyear MTRs at 20psi in the rear and 18psi in the front.  The only flat I ever had was at road pressure while not aired down.
My fullsize Dodge has Yokohama Geolanders and I run 25 rear 20 front.  So far "knock on wood" never had any problems at these pressures.  I think most people are afraid to go that low and at first I was too.  10,000 lb truck you might just have to go very very slow.  Even if you could air down for a soft cushy ride speed will kill your camper.
Stuck Chuck

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Posts: 29
 #9 
I have a '96 F350 with pop up camper. I had Michelin XPS tires with steel side walls. Never had an issue lowering the pressure from 60psi highway to 40ps dirt.

I'm now running wide BFG's and could have lowered to 30psi last december, instead only went to 50psi and the ride was rough going out the south.

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Oobleck

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Posts: 39
 #10 
I KNOW that airing down makes the ride way more comfortable, no question. But I have an F350 crew cab (not dually) with an 11.5' Lance camper in the back. I have always been reluctant to go much below 65 psi. My main concern is that low psi exposes the sidewalls to sharp stones and I guess I'd rather go slow than chew up a tire. What do you all think about the correct air pressure in a ten thousand pound vehicle?

I have also heard opposing opinions about rock punctures in the tread. One side says softer tires are able to bend around rocks so they are less vulnerable. The other says steel bands don't bend all that well and puncture quicker when low psi. Whatcha think?

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