very basic question - tire pressure...

Joined
Sep 26, 2005
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JP, MA 02130
yep, super basic question. sorry.

what i'm wondering is, how do i know what the correct inflation for my 31 x 10.5 radials is for pavement / highway driving with the goal being optimal gas mileage.

to moderately complicate matters, i'm running a fiberglass tub which lightened the 4800lb curb weight of a stock FJ40. by how much? dunno.
 
Joined
Mar 27, 2003
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Georgia Tech
I normally run a 5-10 psi under the max load pressure rating printed on the tire. (remember as you load the truck, your tire PSI raises as well, so you need to leave some leeway.)
 
Joined
Apr 16, 2004
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elizabeth,co
optimal gas milage,just run what the tire says.35lbs and up should roll with little resistance but you will feel like youre rollin on rocks when you hit bumps.
i run 24lbs in my 33" tsl swamps and dont notice bad fuel milage.
 
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Sep 16, 2004
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Emporia, KS
If you spend your time on the road, set the pressure so that you get optimum tread contact. Too low and you'll wear the outside first, too high, the center.
 

scottryana

 
 
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Feb 2, 2004
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Salt Lake City, UT
It takes some time but works pretty well. Find a nice flat dry spot and chalk your tires. Spend a couple of minutes rolling the truck over the pavement and watch the chalk, you should have a nice flat chalk line the width of the tread.

Ryan.
 

krzyabncanuck

USFS HOTSHOT
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Apr 5, 2005
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I agree with the above post about chalk, but will also add that you do not want to turn the front wheels at all, just go straight forward. This has worked for me for years and years.
 
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Dec 9, 2004
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The West
hey if ur really worried theres a company that makes digital guages and it gives the tire pressure for all 4 tires individually. I know its excessive but cool
 
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Jan 3, 2003
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McCall, ID
I agree with the chalk advice and disagree with those advocating running at or near maximum pressure. Maximum is 45 or 50 psi for a lot of tires, and the proper inflation pressure is dependent on the weight of the vehicle they are on, not the maximum they will take. If you overinflate you will get dishing and if you underinflate you'll get cupping and overheating at highway speeds, and either way, you'll end up wearing out your tires faster than they should, as well as lose a margin of safety on the highway.

I think most of us end up with about 26 - 30 psi for on-pavement situations in our FJ40s, which also happens to be what is recommended in the owner's manuals. This is from the bias ply tire days, but it gives you an idea:
tyrepress (Small).jpg
 

erics

 
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Nov 1, 2004
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Iowa
couple observations with an anal "I used to be an engineer type" hat on... key word there is used-to-be so keep the salt shaker handy.

- as originally stated, if the objective is optimal mileage then the corect answer, not taking into consideration other aspects like ride comfort, tire wear and handling/safety issues, is that tire pressure should be as high as possible thus minimizing friction (ie truck rolls easy as possible).

- under those parameters I'd agree with cruisinGA to run a bit under max rated pressure to allow for increases in pressure from changes in temperature and/or volume of air within the tire. Heavier load doesn't necessarily mean higher PSI though... more likely just a differing pavement contact patern.

$.02
 
Joined
Oct 31, 2003
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Fischer, TX
If you run high pressure you don't wear out the inside faster - you wear out the outside slower. I got over 100 k miles on a set of LTX AT's by usually running at close to max pressure.
 
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