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Tire Pressure

Discussion in 'Early CJ5 and CJ6 Tech' started by 57cj5, May 24, 2018.

  1. 57cj5

    57cj5 Member

    out of curiosity, when I drive my 57 in the am when the air is cool, it drives well, no front wobble. However, in the afternoon, it seems to have a slight wobble at about 45 and above.... Tire pressure? Right now I am sitting at 27 in all 4 (BFG KM2s 15x32x11.5).
     
  2. timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

    Maybe. Possible that the profile of your tires changes with increasing temperature. Easy to test ... lower the pressure and see if the wobble goes away. 27 psi is high for a CJ IMO. I run something like 20 front and 16 rear with BFGs in my CJ-6. You can look at the pattern the tire makes and guess at where you are wrt the ideal pressure. Too low and it lifts in the center, too high and it lifts at the edges.

    Note that the closed knuckle axle has some drag built-in, in the form of the greas seals. An open knucle with more freely turning ball joints was routinely fitted with a steering damper by Jeep in the '70s. My '77 J10 (for example) came with a damper from the factory.
     
  3. 57cj5

    57cj5 Member

    Thanks Tim...I was thinking in am cooler temps mean lower pressure...higher temps in afternoon mean higher starting pressure. I wasn't sure how low is too low.
     
    Keys5a likes this.
  4. PeteL

    PeteL If it wasn't for physics, and law enforcement... 2024 Sponsor 2023 Sponsor 2022 Sponsor

    When they come off the rims. :D

    Depends a lot on tire size and vehicle weight. Long thread here recently about determining appropriate pressure. 'Printing' your tires on a flat surface seems to be an approved method for checking street pressure. Sort of a reciprocal of wear patterns.

    But yeah 27psi is high.
     
  5. Daryl

    Daryl Sponsor

    I just had to raise the pressure in my Maxxis bighorns. Running 12 psi was starting to wear the blocks a little. I went up to 18 and they seem happier.
     
  6. 1960willyscj5

    1960willyscj5 Well-Known Member

    I am old. Grew up before metric tires came into vogue. I learned to inflate my tires to 32 psi all the way around. When the transition to metric started the tire guys never really said anything about running lower pressures, or if they did, it was something like 28 psi. Which felt low to us at the time.
    I still set my tires to 32 psi. And I have been informed lately by the different installers that I should run my tires at close to the maximum recommended pressure on the sidewall. Can be rather confussing, to say the least.
     
  7. sterlclan

    sterlclan Member 2024 Sponsor 2022 Sponsor

    I run an lt 235/85/16 load range e ten ply tire the sidewall says 2800 lbs at 80 psi. Not going to happen. I run 22 psi front 18 psi rear get a full contact patch on the ground and great wear.
     
    Daryl likes this.
  8. 57cj5

    57cj5 Member

    Do you have a link to the thread or search words?
     
  9. timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

  10. PeteL

    PeteL If it wasn't for physics, and law enforcement... 2024 Sponsor 2023 Sponsor 2022 Sponsor

  11. ronnie victor

    ronnie victor Member

    FWIW, my FSM for my 66 CJ5 F4 states in the ''wheels" chapter: 26 psi front; 28 psi rear.
     
  12. Howard Eisenhauer

    Howard Eisenhauer Administrator Staff Member

    It's going to depend on tire size- skinny tires take more pressure than wide ones.

    Stock tire sizes in the 60's would have been around 7" or so tread width.

    Standard inflation for NDT's is 32/30 PSI; I run mine at 28/26, anything less than that going around corners gets exciting & not in a good way :(
     
  13. Wenaha

    Wenaha Member

    This is a very reasonable approach. Almost all tire services, dealer shops, etc. will inflate your tires to max recommended pressure. I am running 215/85/R16 Cooper STT Pro tires (load range E) Running them at the recommended 80 PSI is nuts. I deflate until a get good contact on a flat surface and they feel good driving.

    On mt F350 I am running Goodrich 285/75/R16 ATs. Load range E. I use the same approach to setting pressure, and it usually works out to about 65 PSI (not 80). If I am towing my Airstream or boat, I'll increase rear tires and slightly increase front tires.

    Works for me.
     
  14. supertrooper

    supertrooper Member

    I have 33x12.5 MTs and run 22psi on the street. The chalk test that timgr posted is the best way to know what pressure is best for your vehicle.
     
  15. CJeep5

    CJeep5 New Member

    I have 35x12.50-15 MTR's that I have at 20 psi, well that's where I ran them til I parked her a while back. Now they have probably 10 psi and HUGE flat spots! All to be worked out soon.