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How much tire pressure do i need???

Discussion in 'The Garage' started by George_Pimpdaddy, Jul 25, 2005.

  1. George_Pimpdaddy

    George_Pimpdaddy 1/2 ton status

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    Hey i was just wondering what most people run in there blazers for pressure?
    I have a 89 full blazer with 31 bfg all terrains and a posi in the rear currently i aim for about 40psi up front and about 44 in the rear does this sound right?
    thanks for any input :D

    [​IMG]
    89 silverado 355TBI/700r4/np241
    10 bolts auburn posi in rear
     
  2. az-k5

    az-k5 1/2 ton status

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    To much air IMO. For an unloaded complete K5 with 31's you should be around 29-35 psi depending on driving style are type of tire. I would say that 32 psi will give you a better ride and keep the same handling.
     
  3. dyeager535

    dyeager535 1 ton status Premium Member

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    If I'm wrong I welcome someone correcting me, but I believe that just because you CAN run more PSI than called for in the manual, doesn't mean that you should.

    Too little or too much air increases tire wear.

    I know it's a lot more complex than that, but again, as a general rule, for "regular" use, you should use what the vehicle manufacturer spec'd.

    My dad ran his tires around 40-44, and they wore the centers out pretty quick.
     
  4. Thunder

    Thunder 3/4 ton status

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    I used to run my AT 31s at 35 PSI front and rear un loaded . On Trips Loaded up or towing I would up the pressure to 40-42 LBS.
    Sticker on the door of my 89 says 32 up front and 35 rear. 35 was the best all around pressure for me. Got the best tread wear and fuel MPG
     
  5. jarheadk5

    jarheadk5 1/2 ton status

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    My 33x12.5-15 BFG AT's have a maximum cold inflation pressure of 35psi right on the sidewall; I don't imagine your 31's max pressure is much different. You're likely running 20-30% overinflated. As already noted, this'll wear down the center of your tread pretty quickly.

    Why run higher pressure in the rear? Unless you're pulling a trailer or carrying a lot of crap in the back, a stock-bodied K5 is somewhat front-heavy. You want more pressure in the front tires than the rears in this case.

    I highly recommend you look at the sidewall of your tires, find the max cold inflation pressure, and air down to that at the very least. Overinflation isn't as bad for the tire as underinflation, but it's still not good.
     
  6. pauly383

    pauly383 Daddy383 Staff Member Moderator

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    I run my 33's at 30 right now . 28 is as low as I have been on the street without it feeling funny . Anything over 35 or over feels rough . I get real even tire wear too , and run a locker .

    I ran my 31's at 32-35 street and never aired down on trail until CK5 , now I air down on trail .
     
  7. CustomChevy

    CustomChevy 1/2 ton status

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    what do you like to air down to on trail. I as well am new to this concept (from CK5).


    i run 33x12.5x15 BFG mud-terrains
     
  8. stizkidz

    stizkidz 1/2 ton status

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    Most major tire centers will inflate newly installed car tires to 31 psi and most truck tires to 35 psi. However, I have seen Load C and up range tires inflated to tire spec, which can be upwards of 50 psi.
     
  9. BigCountryx

    BigCountryx 1/2 ton status

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    You want complicated or simple, you can figure it out either way. Clicky Here

    I figured out my pressure the mathmatical way when I had my 38" SSR's on my old Z. Basicly, You have to figure out what I call the X Factor. That i your tires Max Load Capacity / Your tires Max Pressure. Once you know the X Factor, Actual weight on the tire / X + Required PSI. So for instance I had weighed my truck at work front and rear. I divided front by 2 and rear by 2 to find out how much weight was on each tire. Then, My max tire Pressure was listed as 65psi and my Max Load Capacity was 3640lbs. Each front tire supported 1630lbs and my rears supported 1030lbs.

    3640/65=56 (X Factor)

    Front
    1630/56=29.11psi (I ran 30)

    Rear
    1030/56=18.39psi (I ran 20)

    Chalk test showed all good and tires lasted well. I also went to 25psi rears when towing my bassboat. (20')

    Or you could just Real World DIY



    1. The "Business Card Test": On a smooth, hard surface, try inserting a business card between the tire and the pavement. If it goes in less than about 3mm-1/8", the the tire may be under-inflated, if it goes in more than about 6mm-1/4", it may be overinflated.
    2. The "Chalk Line Test": Draw a heavy chalk line across al the trear faces. drive slowly forward in a straight line for a few revolutions of the tire. Get out and observe the wear pattern of the chalk. If it has worn away evenly, then the inflation is correct. If either the edge or center of the line is worn first, then the tire is under or over inflated, respectively.
    3. The "Water Puddle Test": Similar to test #2, but drive through a puddle of water in a straight line, then get out and observe the wet tire tracks and see if the wet imprint is even, especially as the track starts to dry out after a few revolutions.
    4. Heat is the #1 enemy of high-speed tires. The flexing of the tire's sidewalls as the tire rolls under load is the source of the heat. Higher inflation pressures mean less flexing of the sidewall and therefore less heat. Another test for proper inflation pressure is to measure the tire pressure when cold then again after 15 minutes at highway speed. If the pressure rise due to the temperature rise is more than about 3 psi, then the tire may be under-inflated.
     
  10. southernspeed

    southernspeed 1/2 ton status GMOTM Winner

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    I run 30/35 in my '91 with 31" BFG M/T and 20 all round on my '78 with 35's
     
  11. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    I run 17 psi using the "Complicated Method"....


    Lots of footprint + not much curb weight = low tire pressure (but correct)
     
  12. Blue85

    Blue85 Troll Premium Member

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    That is correct. The bigger your tires, the lower the pressure you need.

    Remember tire pressure is measured in PSI (pounds per square inch). When the contact patch grows, you have more square inches, so to support the same weight, the pressure is lower.

    I run 25 rear 28 front with 35's

    Overinflation is a great way to make a vehicle ride terribly.
     
  13. RootBreaker

    RootBreaker 3/4 ton status Premium Member

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    dont forget if your tires are not stock from the dealer you wanna look at the tire for max pressure and see what is comfortable to you...

    my hawgs are max 30psi... I run 24 all around.... and my sides still arent all the way on the ground...
     
  14. 6.2LTrailblazer84

    6.2LTrailblazer84 1/2 ton status

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    Anyone ever read Fear and Loathing in las Vegas? There is one part where Hunter Thompson is in some big convertible and fills the air in the tires to MAX because the suspension was soft...felt loose. He went well beyond the max, I believe. After reading this I attempted the same, though not quite to the same degree, and I thought I felt a noticible difference in a firmer handling vehicle --less wander.
     
  15. RootBreaker

    RootBreaker 3/4 ton status Premium Member

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    and a DEATH TRAP at highway spees when they all go POP!!!!!
     
  16. 6.2LTrailblazer84

    6.2LTrailblazer84 1/2 ton status

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    Why do they have a minimum and maximum pressure then if it is that dangerous?

    I probably wasn't clear enough. I didn't go over my max tire pressure, but I was near it.
     
  17. BigCountryx

    BigCountryx 1/2 ton status

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    Really, it's the higher the load capacity of the tire, the lower the pressure you need isn't it. If you have a large tire with a low load capacity, your statement would not hold true. (Although there may not be large tires with very low load capacity, I have not checked into that)
     
  18. George_Pimpdaddy

    George_Pimpdaddy 1/2 ton status

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    thanks for the help i adjusted my tires to 35psi now and am noticing a smoother ride especially on our bumpy roads also the tire dealer had my rear pumped up to 45 when they installed them....
     

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