very basic question - tire pressure...

Discussion in '40- & 55-Series Tech' started by JP_FJ40, Nov 9, 2005.

  1. JP_FJ40

    JP_FJ40

    Messages:
    86
    Likes Received:
    0
    Joined:
    Sep 26, 2005
    Location:
    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.
     
  2. CruisinGA

    CruisinGA

    Messages:
    6,168
    Likes Received:
    16
    Joined:
    Mar 27, 2003
    Location:
    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.)
     
  3. Magoo

    Magoo

    Messages:
    383
    Likes Received:
    1
    Joined:
    Apr 16, 2004
    Location:
    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.
     
  4. trainrech

    trainrech

    Messages:
    2,797
    Likes Received:
    130
    Joined:
    Sep 16, 2004
    Location:
    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.
     
  5. scottryana

    scottryana

    Messages:
    9,928
    Media:
    1
    Albums:
    2
    Likes Received:
    7,070
    Joined:
    Feb 2, 2004
    Location:
    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.
     
  6. krzyabncanuck

    krzyabncanuck USFS HOTSHOT

    Messages:
    8,717
    Likes Received:
    735
    Joined:
    Apr 5, 2005
    Location:
    NC
    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.
     
  7. JP_FJ40

    JP_FJ40

    Messages:
    86
    Likes Received:
    0
    Joined:
    Sep 26, 2005
    Location:
    JP, MA 02130
    cool, thanks for the input.
     
  8. okie

    okie

    Messages:
    1,456
    Likes Received:
    1
    Joined:
    Dec 9, 2004
    Location:
    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
     
  9. IDave

    IDave

    Messages:
    7,167
    Media:
    1
    Albums:
    1
    Likes Received:
    28
    Joined:
    Jan 3, 2003
    Location:
    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
     
  10. erics

    erics

    Messages:
    1,337
    Likes Received:
    81
    Joined:
    Nov 1, 2004
    Location:
    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
     
  11. SteveLCetc

    SteveLCetc

    Messages:
    2,373
    Likes Received:
    9
    Joined:
    Oct 31, 2003
    Location:
    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.
     
  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.