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Technical Rookie question on bias ply air pressure

Discussion in 'The Hokey Ass Message Board' started by Knghtcadi, Apr 23, 2018.

  1. Knghtcadi
    Joined: Oct 17, 2016
    Posts: 361

    Knghtcadi

  2. Hnstray
    Joined: Aug 23, 2009
    Posts: 10,684

    Hnstray
    ALLIANCE MEMBER
    from Quincy, IL

    26 to 32 psi.....I personally would try 30 psi and see how I liked the ride and handling. Adjust as necessary.

    Ray
     
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  3. Knghtcadi
    Joined: Oct 17, 2016
    Posts: 361

    Knghtcadi

    Ok thanks I’ll try it


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  4. On my '59 Ford with radials, started with 32 in the back and it bounced quite a bit, dropped it to 30 and better. I'll try 28 psi next. With old cars and bias ply tires, we used to put 28 psi in the tires across the board.
     
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  5. TagMan
    Joined: Dec 12, 2002
    Posts: 5,868

    TagMan
    ALLIANCE MEMBER

    Buy an Owner's manual or see if there's one online you can access for free and it'll tell you exactly what pressure to use.
     
  6. squirrel
    Joined: Sep 23, 2004
    Posts: 43,458

    squirrel
    Member

    or google it, 26 front, 24 rear.
     
  7. porknbeaner
    Joined: Sep 12, 2003
    Posts: 41,063

    porknbeaner
    Member

    Standard tire size for 1954 Mercury Monterey Custom 4-Door Sedan:
    (in case of different tires in front and rear the dimensional data are valid for driving or rear wheels)

    Standard tire size:


    7.10 - 15


    Tire width (mm):


    180


    Tire sidewall factor:


    90


    Rim size (in):


    15


    Total wheel diameter (mm / in):


    705 / 27.8


    Tire air pressure (cold):




    Front:


    180 kPa / 26 psi / 1.8 atm / 1.8 bar


    Rear:


    165 kPa / 24 psi / 1.6 atm / 1.7 bar


    Maybe this will help. I found the specs online for you.



    Edit damnit: Damnit Jim ( @squirrel ) you type faster than I cut n paste.:eek::p:D:D:D
     
  8. Hnstray
    Joined: Aug 23, 2009
    Posts: 10,684

    Hnstray
    ALLIANCE MEMBER
    from Quincy, IL

    Manufacturer's recommended tire pressures in that era were biased (no pun intended) toward maximizing ride comfort, not handling. Adding a few pounds to minimize side wall deflection in turns was common practice. Also, tires have a range of recommended tire pressures, depending on loading. Such information is/was published by tire manufacturers. Take the auto factory specs with a 'grain of salt'.

    As a general proposition, a bit more pressure is less detrimental to the tire than than too little.

    Ray
     
    Last edited: Apr 24, 2018
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  9. Knghtcadi
    Joined: Oct 17, 2016
    Posts: 361

    Knghtcadi

    Cool thanks


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  10. squirrel
    Joined: Sep 23, 2004
    Posts: 43,458

    squirrel
    Member

    yup, nice and mushy at factory specs...which is what you want, in a stocker or mild custom, right?
     
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  11. Rusty O'Toole
    Joined: Sep 17, 2006
    Posts: 8,994

    Rusty O'Toole
    Member

    26 in front 28 in back for that soft boulevard ride. 32 all around for fast road use.
     
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  12. porknbeaner
    Joined: Sep 12, 2003
    Posts: 41,063

    porknbeaner
    Member

    Here is the thing with tires and pressures. The factory especially in that time era was concerned with ride quality. Once fuel mileage became and issue they started upping tire pressures.

    The old man used to run his tires softer around town than out on the highway, on a rod trip they were brick hard and in town they were not. Low tire pressures means two things, tire heat and poor mileage ( generally speaking). My take on it is if you are going to be driving it for the next 4 hours keep 'em hard and if you are just hitting the local hot dog stands run 'em softer.
     
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  13. Knghtcadi
    Joined: Oct 17, 2016
    Posts: 361

    Knghtcadi

    These were the answers I was looking for , I’m going to a show this weekend which I’ll probably go a couple hundred miles of freeway , back roads and around town so I’m sure pumping them up will get it done


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  14. See how bouncy the rear is. My Ford was terrible at 32 in the rear, I really have to set all my pressures soon.
     
  15. Los_Control
    Joined: Oct 7, 2016
    Posts: 602

    Los_Control
    Member
    from TX

    I was taught, the air pressure is the tool that carries the load.
    you can have a tire with 0 psi, technically it is not under inflated if it is not carrying a load.
    If you are going to load 6 kegs of beer in the back of the desoto, you may want to bump the air pressure to max.
    The max rating listed on the sidewall, is for safety concerns.
    You do not want to lift 3 tons with a crane rated for 2 tons.

    If the tire says 32 psi max on the sidewall, that does not mean you should run 32 psi in it, just do not run more then that. 26/24 sounds like a great starting point
     
  16. porknbeaner
    Joined: Sep 12, 2003
    Posts: 41,063

    porknbeaner
    Member

    Remember its a Ford not a Buick. :D :D :D

    Most of these old hoopties rode like lumber wagons when you got the pressure up there. A kid I went to high school with had a '58 post car. He always wanted me to check the air pressure when he brought his car into the station and always made a big deal out of he wanted exactly 28 and 30. I finally got smart and just handed him the gauge when he came in.

    I think that it takes a bit of playing to get them right. We play with the drivetrain, change the tires, gas shocks or hydraulic. I think it all makes a difference. ;)
     
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  17. Rusty O'Toole
    Joined: Sep 17, 2006
    Posts: 8,994

    Rusty O'Toole
    Member

    If you want to get all propellerhead about it...

    Your car is supported on a column of air above the contact patch of the tire. The contact patch is the ideal, oval patch of rubber that contacts the ground. If you have the ideal pressure it will be the perfect size, not too big or too small, with the same pressure all across not lighter in the middle (underinflated) or ligher on the edges (overinflated).

    So to find the ideal air pressure weigh each corner of the car individually. Calculate the square inches of tire patch you ideally should have. Divide that number into the weight in pounds to find out how many pounds per square inch of air you need.

    Something to keep you amused on a rainy afternoon.
     
  18. porknbeaner
    Joined: Sep 12, 2003
    Posts: 41,063

    porknbeaner
    Member

    Or just make a chalk line across the tire and keep playing with it til the line disappears evenly. LOL

    That's backyard applied physics at its best. ;)
     
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  19. Hnstray
    Joined: Aug 23, 2009
    Posts: 10,684

    Hnstray
    ALLIANCE MEMBER
    from Quincy, IL

    ^^^^^^^^^^^

    Benno.......you NEVER disappoint! :D

    Ray
     
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  20. Knghtcadi
    Joined: Oct 17, 2016
    Posts: 361

    Knghtcadi

    I save that for my front end alignment


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  21. AndersF
    Joined: Feb 16, 2013
    Posts: 627

    AndersF
    Member

    I like to have the pressure on the low side.
    High pressure seems to make the tires more sensible to follow grooves on the road.
     
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  22. chevy57dude
    Joined: Dec 10, 2007
    Posts: 5,001

    chevy57dude
    Member

    Reading and absorbing here. Beaner - you are my hero. Rusty, great explanation. Makes sense. Probably I need to lower the air pressure in my fronts.
     
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  23. Here's a fact, inflate all four bias ply tires to a minimum of 32 psi and it will almost entirely eliminate squirreling at hiway speeds on any vehicle!
     
  24. Truck64
    Joined: Oct 18, 2015
    Posts: 3,584

    Truck64
    Member
    from Ioway

    Super high tire pressure does decrease rolling resistance but it just pounds the hell out of wheel bearings not to mention rattles yer fillings.
     
  25. Knghtcadi
    Joined: Oct 17, 2016
    Posts: 361

    Knghtcadi

    So I put 32 in all four tires today , def handles better but has some slight squiling in sharp turns


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  26. Hnstray
    Joined: Aug 23, 2009
    Posts: 10,684

    Hnstray
    ALLIANCE MEMBER
    from Quincy, IL

    That could be .....a) natural tire scrub.....b) alignment issues......c) non-stock wheel offset...d) all of the preceding.....

    I would try to get an accurate measurement of toe-in...be sure is is set correctly. Toe errors can/will wear tires rapidly. If you can find a competent shop that will do a full alignment, that might be worth considering.

    Ray
     
  27. Knghtcadi
    Joined: Oct 17, 2016
    Posts: 361

    Knghtcadi

    It’s def a alignment issue I need to get it aligned again , I had it done last summer but I knew it was wrong and the shop wouldn’t give me print out so I know it was off


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  28. Ned Ludd
    Joined: May 15, 2009
    Posts: 3,864

    Ned Ludd
    Member

    In other words, the air pressure should be proportional to the car's weight distribution. It's what I run on my DD (modern 50-series radials at 38PSI front and 26PSI rear – handles well) but I derived it differently. Increasing air pressure in a tyre affects its sidewall deformation or slip-angle resistance exactly the same as decreasing the load on the tyre. The tyre can't differentiate between carrying 700lbs @ 38PSI and carrying 480lbs @ 26PSI.

    The idea here is to get the tyres to respond to the roll-stiffness bias (i.e. lateral weight transfer distribution) rather than the weight distribution. In the case of the DD it just tunes out that ridiculously idiot-proof excess of understeer you generally find in a small hatchback.
     
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  29. porknbeaner
    Joined: Sep 12, 2003
    Posts: 41,063

    porknbeaner
    Member

    Just to middy up the water and rattle a tree or two.

    I am surprised that no one has come up with filling them with nitrogen instead of air. :rolleyes:
     
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