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Tire Pressure

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by TXsizeK5, May 6, 2002.

  1. TXsizeK5

    TXsizeK5 1/2 ton status

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    Whats optimum tire pressure on the highway for 35x12.50/15 BFG mud terrain for best wear and hieght. Mine are a little worn and running like 25psi and they sit like 33's i would like to air em up a bit to get a lil higher up and a lil better gas meilage so i've heard.
     
  2. KRAZIE87K5

    KRAZIE87K5 1/2 ton status

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    DAMN! Only 25lbs for street use? Yikes... I run 35lbs in my BIAS PLY 36" TSLs. Cuts road noise, and that seems to be where they sit "flatest" on the road. Off road, I'm down to 15lbs on a 16.5" rim...

    -Dan
     
  3. RedDwarf

    RedDwarf 1/2 ton status

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    Try 20 psi. I used to run 18-20 when I ran 35" tires.

    35psi is for car tires
     
  4. MudbogAD

    MudbogAD 1/2 ton status

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    I run 35 psi in my 35's.
     
  5. dyeager535

    dyeager535 1 ton status Premium Member

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    I tried 45PSI in my BFG AT's for awhile, but I didn't like the way it felt when I hit bumps. It didn't noticeably increase my MPg over 35PSI either, so thats what I'm back to. Not sure how high yours are rated PSI-wise though, I think mine are 50 or 55PSI max.
     
  6. ds350

    ds350 1/2 ton status

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    I usually run my 33's at about 32 PSI. Anything more and I can feel every bump and the steering wheel becomes ultra sensitive.

    Danny
     
  7. Blue85

    Blue85 Troll Premium Member

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    I read an article in 4WPW catalog that claims your ideal pressure is just a function of weight on the tire. You take the maximum rated pressure and the maximum rated weight and take that as one point. You then decrease the pressure linearly to the same proportion that the weight on that tire is less than the max rated weight. Pressure=(max pressure*actual weight)/(max weight) Example: A hypothetical tire rated at 45psi max and 3400lbs max, carrying 2200lbs would need about 29psi. They say that this is why the manufacturers put those numbers on the sidewall.

    Does anyone know whether or not this is right?

    Even if you don't know the exact front/rear ratio or total weight, it could still get you in the right ballpark.
     
  8. René

    René 1/2 ton status

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    According to a list of BF Goodrich, the correct air pressure would be 22 psi in front and 19 psi in the back. I assume the blazer weighs 2900 lbs in front and 2580 lbs in the back. With the M1009, the Army manual recommends for a 31x10.5 R 15, 41 psi. If I convert this value now, I come to 26 psi for the 35”.
    I would not fall below this value, because it can become dangerous with broad rims...
     
  9. René

    René 1/2 ton status

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    I’ve never heard about this formula, but it seems to be correct.
     
  10. Ben Malinski

    Ben Malinski Guest

    I thought tire pressure was what the automotive manufacture suggested? Afterall, they built the vehicle. But then again, they did not take into consideration the aftermarket add ons, etc.
    Just my 2 cents worth; pressure should be at whatever makes your feel comfortable while driving. Each vehicle is different so no two will be the same. Experiment with the pressure!
     
  11. rampage

    rampage 1/2 ton status

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    I've heard the best way to determine the correct pressure is to make sure the tire contacts the pavement evenly. To do this put something like chalk on your tire and drive it so that the wheel make one revolution. Then notice what the tread pattern on the pavement looks like and where the chalk is worn off on the tire. If there is alot of chalk left on the inside/outside of the tread then the pressure is too high. If the chalk remains on the center of the tire then the pressure is too low. It should wear off evenly.
     
  12. Blue85

    Blue85 Troll Premium Member

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    Manufacturer's recommendations are meaningless once you change to a different size tire. Even when changing to a different brand of the same size can effect the ideal pressure.

    The bigger the tire is, the less pressure it will need to support a given weight. If you have more square inches of surface area on the inside, you need fewer pounds per square inch (psi) to support the same number of pounds.
     
  13. txbartman

    txbartman 1/2 ton status

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    Depends on what you are trying to achieve as to what the best pressure is. If you want the best mileage, go with as much pressure as you can. That will lead to less tire impacting the pavement. The less rubber that meats the ground, the lower the drag. But, then your tires will wear unevenly.

    I run mine at 35-38 PSI on highway trips. Around town and normal use, I run theme between 32 and 35 PSI. Offroad, I run have run as little as 12, but usually run around 18-22 PSI.

    Experiment a little to see what is best for you.
     
  14. kilroy

    kilroy Registered Member

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    off-road adventures just had an indepth artical on this in thier April/May issue. the artical is not on line, but I can look at it tonight and get back with you. RENE' s post should be close.
     
  15. morphed86k10

    morphed86k10 1/2 ton status

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    The width of the rim has a lot to do with it also. For ideal tread contact you'll need a lot less air with a narrow rim compared to a wider one. With my 35 inch BFG's on a 8.25 inch wide rim, the outer lugs hardley hit the dirt even with 25 psi in them (load range D tire). It's noticable when going from dirt to pavement, the dirt stays on the the outer parts a bit longer than it does the center of the tread. The load range has a lot to do with how much pressure you'll run.
     
  16. zakk

    zakk 1/2 ton status

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    double damn! I run 17 pounds on the 39.5's on the street! and air down to 12-13 when I am gettin' it.

    Rita made it through frame twister on 17 pounds.
     
  17. behemoth

    behemoth 1/2 ton status

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    Several people have hit it on the head. Correct tire pressure is a factor of vehicle load. There is a very long winded article in the most recent 4 Wheel Parts Warehouse magazine/catalog outlining several lengthy procedures in determining correct tire pressure "for YOUR vehicle" and "YOUR style of driving". I haven't gone through these procedures yet, but I will.
     
  18. RedDwarf

    RedDwarf 1/2 ton status

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    Bigger tires don't need as much pressure to support the same weight as smaller tires.

    The above mentioned article should be read by those who are confused about this issue and by those running "whatever it says on the door jamb".
     
  19. behemoth

    behemoth 1/2 ton status

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    Exactly! Whatever is marked on the tire (35 psi, etc.) doesn't mean that's what it should be "under all driving conditions". There's a very wide range.
     
  20. kilroy

    kilroy Registered Member

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    Ok here is some of the info derived from the off-road adventures article. The info in () is specific to my truck.

    Method 1: look on the internet for a load vs inflation chart for your tires on the manufactures web site, some have them posted and some do not.

    Method 2: create your own chart;
    1. The pressure listed on the tire is the max pressure at max load (35 psi at 2225 lbs)
    2. The load of your truck should be listed on a sticker on the door (3190 front / 3550 rear), divide each in half to get your load for each tire (1595 each front / 1775 each rear). If you carry a lot of extra weight factor this into your load information. You can also go to a scale and get an actual reading of your front/rear weight.
    3. Make a chart using the info from step 1, doing this on graph paper is easiest.

    …....2300
    …....2200


    ….. thru

    lbs
    ……..200
    ……..100
    ………...0 1 2 thru 34 35
    ………………. psi


    4. Locate the point where your info from step 1 come together, draw a diagonal line from this point to 0.
    5. Locate your load for each front tire on the lbs scale of the chart (1595), draw a line across the chart until you intersect the line from step 4, at the point your lines intersect draw a line straight down the chart. This is your tire pressure for the front (25). Repeat for rear tire (1775 lbs ) (28 psi)

    Method 3: is the hardest and takes the longest, but if done correctly can be the most accurate. Has already been discussed in this post by rampage.

    Note: A tire filled with a few extra pounds of air is less likely to cause problems than a tire that is under inflated.
     

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