1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

tire pressure

Discussion in '40- & 55-Series Tech' started by drohweder, Mar 13, 2004.

  1. drohweder

    drohweder

    Messages:
    1,145
    Likes Received:
    1
    Joined:
    Oct 5, 2003
    Location:
    Golden, CO
    I've got a set of Big-O MTs 35x12.5 on my FJ55. Recently I had someone tell me my tires were overinflated at 35psi and I should be running 28.5-30psi for on the road. I aired them down and everything seems the same except that they are much more noisy.

    What pressure is best for around town driving on these MTs? Thanks :cheers:
     
  2. 73lndcrsr

    73lndcrsr SILVER Star

    Messages:
    745
    Likes Received:
    4
    Joined:
    May 28, 2002
    I had some 33 procomp MTs a short while ago. I had to run about 26 psi for the best contact patch on road. Not sure if it helps, but should give you a starting place. I run 18 psi in the 36" SXs now.
     
  3. burnt03

    burnt03

    Messages:
    259
    Likes Received:
    1
    Joined:
    Oct 1, 2002
    Location:
    Peachland, BC, Canada
    Someone told me once that if you take a piece of chalk and draw a line across the tread then roll it forward and see what sort of mark you leave on the road, it'll give you a good idea whether your tire is over/underinflated. Once you get a line the same length as what you drew on the tire, it should be good to go.
     
  4. 60wag

    60wag SILVER Star

    Messages:
    1,922
    Likes Received:
    36
    Joined:
    Jun 25, 2003
    Location:
    Boulder, CO
    I've wondered about the the inflation pressure myself. I run BFG ATs 33x10.5 at 32 psi on the road but have no clue as to whether its optimal for milage and wet weather handling. The chalk line idea sounds good to me.
     
  5. desertdude

    desertdude SILVER Star

    Messages:
    3,308
    Likes Received:
    116
    Joined:
    Nov 29, 2003
    Location:
    Arizona
  6. kling-on

    kling-on Kool Arrow

    Messages:
    5,465
    Media:
    12
    Albums:
    1
    Likes Received:
    92
    Joined:
    Apr 26, 2003
    Location:
    Pimpin part in SanAntonio TX
    Get a full lug on the ground then take a bussiness card and stick it under the tread air up or down till only a 1/4 in stick under the tread block this will give you the contact patch for YOUR set up ...all this changes with whgt :cheers:

    Old tire guy trick ;)
     
  7. IDave

    IDave

    Messages:
    7,168
    Media:
    1
    Albums:
    1
    Likes Received:
    21
    Joined:
    Jan 3, 2003
    Location:
    McCall, ID
    Sorry, Kling-on, but I haven't had enough coffee this morning to follow that! I am interested, though.

    I am struggling with this issue, too. For my 71 FJ40 the owner's manual sez 18 psi, no questions asked, on the chart for unladen. Seem low to you, too? Well, on another page, they say, add 6 lbs for nebulous conditions. Still seem low? Well, I had my friendly tire guy (who really is a personal friend) look into it. The have a "book" that lists recommended pressures according to vehicle model, etc. For my vehicle? 28 psi, no questions asked. Now consider. Bias ply tires when these rigs came out. Nowadays, we are all running radials. Sidewall height. You don't want them bulging out too much, right? Bulges at 18psi, but it does some at 26, too. How much is too much bulging?

    I wish I could say I have the answer.
     
  8. Landpimp

    Landpimp

    Messages:
    15,720
    Likes Received:
    1,727
    Joined:
    Mar 14, 2003
    Location:
    Gig Harbor WA
    this might help......
    http://www.safari4x4.com.au/80scool/tech/tyre_pressures.html

    A subject which often pops up is the correct road tyre pressure for our Cruisers.
    Here's the deal.... Check the tyre pressure cold. Hit the road for half an hour, stop and check the tyre pressures. You're aiming for a 4psi pressure increase (due to heat). This will give you the right pressure to run for your tyre/axle load and speed combination. If it's greater than 4psi, you need to run more pressure. If less than 4psi, they're over inflated and you need to drop the cold pressure.

    This may however not be the ideal pressure. You may for example increase the pressure by a couple of psi for sharper handling or decrease slightly for more comfort. You may also use more pressure at the front to decrease the amount of understeer.

    Stiff sidewall tyres such as the BFG will require quite high pressure compared to a road based tyres such as the GrandPuke. A stiff sidewall will generate more heat. The general rule for road based tyres is to not exceed 36psi no matter what. With the 285/75x16 BFG, it's not uncommon to pump them up to 65psi when running fast and heavily loaded.

    gc
     
  9. lowtideride

    lowtideride

    Messages:
    7,605
    Media:
    12
    Albums:
    1
    Likes Received:
    78
    Joined:
    Sep 29, 2003
    Location:
    The Sunshine State
    i just put a set set of 35s ( mud rovers) about 400 miles ago and i noticed that the sides of the tread still have the lil nubby things on it.. im running at 35 psi, should that whole tread of the tire be touching the ground? i noticed that the 35s give less side flex than the 31s i had on it before... so im starting to think 35psi is too much/?????
     
  10. IDave

    IDave

    Messages:
    7,168
    Media:
    1
    Albums:
    1
    Likes Received:
    21
    Joined:
    Jan 3, 2003
    Location:
    McCall, ID
    I'd say you're definitely overinflated, lowtide! Those nubbies should wear off evenly.
     
  11. lowtideride

    lowtideride

    Messages:
    7,605
    Media:
    12
    Albums:
    1
    Likes Received:
    78
    Joined:
    Sep 29, 2003
    Location:
    The Sunshine State
    yulp ill air down tomorrow
     
  12. kling-on

    kling-on Kool Arrow

    Messages:
    5,465
    Media:
    12
    Albums:
    1
    Likes Received:
    92
    Joined:
    Apr 26, 2003
    Location:
    Pimpin part in SanAntonio TX
    [quote author=IDave link=board=1;threadid=13063;start=msg120948#msg120948 date=1079280105]
    Sorry, Kling-on, but I haven't had enough coffee this morning to follow that! I am interested, though.

    I am struggling with this issue, too. For my 71 FJ40 the owner's manual sez 18 psi, no questions asked, on the chart for unladen. Seem low to you, too? Well, on another page, they say, add 6 lbs for nebulous conditions. Still seem low? Well, I had my friendly tire guy (who really is a personal friend) look into it. The have a "book" that lists recommended pressures according to vehicle model, etc. For my vehicle? 28 psi, no questions asked. Now consider. Bias ply tires when these rigs came out. Nowadays, we are all running radials. Sidewall height. You don't want them bulging out too much, right? Bulges at 18psi, but it does some at 26, too. How much is too much bulging?

    I wish I could say I have the answer.
    [/quote]

    OK its late I'll try again ..... most mud tires have two or three stage lugs ... if tow go with the bigger it three chose the middle ... if its a A/t they should be the same.... make a mark on a bussiness 1/4 in from the edge, push this lightly under the tire till it stops. ajust the air in the tire till it stops at the line , this will give you the tire preshure for your whgt on that axle for that tire. the owners manual is a average not the fits all ...71 fj40 well thats a true 4 ply bias 7in wide and 28in tall tire... are you still running those and are you not hauling any stuff ??? all this stuff changes what the tires "NEED" in them to run right and last


    ...is thay better
     
  13. fsusteve

    fsusteve

    Messages:
    3,802
    Media:
    18
    Albums:
    1
    Likes Received:
    48
    Joined:
    Aug 2, 2003
    Location:
    Naples/Big Pine Key, Fl
    [quote author=lowtideride link=board=1;threadid=13063;start=msg120982#msg120982 date=1079285256]
    i just put a set set of 35s ( mud rovers) about 400 miles ago and i noticed that the sides of the tread still have the lil nubby things on it.. im running at 35 psi, should that whole tread of the tire be touching the ground? i noticed that the 35s give less side flex than the 31s i had on it before... so im starting to think 35psi is too much/?????
    [/quote]

    Al, I think the problem is those tires are just to big for yer truck. I'm going out on a limb here but to help out a friend I'd be willing to swap tires with ya. ::)
     
  14. woody

    woody unhelpful spotter Staff Member Admin

    Messages:
    10,619
    Media:
    317
    Albums:
    7
    Likes Received:
    1,873
    Joined:
    Jan 15, 2002
    Location:
    Toquerville UT
  15. IDave

    IDave

    Messages:
    7,168
    Media:
    1
    Albums:
    1
    Likes Received:
    21
    Joined:
    Jan 3, 2003
    Location:
    McCall, ID
    Thanks, Kling-on. I got it, except I'm not sure what you mean by "stage lug". This explanation is similar to what the tech article Woody refers to states, IIRC. There's "no one size fits all," for sure, but I would bet for most of us it comes in under 30 psi for most applications.
     
  16. lowtideride

    lowtideride

    Messages:
    7,605
    Media:
    12
    Albums:
    1
    Likes Received:
    78
    Joined:
    Sep 29, 2003
    Location:
    The Sunshine State
    steve, yeah we can swap tires.but just the front two, i want that cool hot rod lowered front end look