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Tire pressure with bigger tires

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by dremu, Apr 24, 2003.

  1. dremu

    dremu Officious Thread Derailer Premium Member

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    Just upgraded my 74 /forums/images/graemlins/k5.gif from 31x10.50's to 33x12.50's. I was running about 40psi on the street, on Michelin all-seasons. The 33"s are BFG AT's (both on factory 15x8 ralleys.)

    I know about the chalk trick and so forth, but I thought I might poll y'all and see if any of you had any recommendations or experience. I remember when I switched my 3/4ton /forums/images/graemlins/burb.gif to wider rubber (265 instead of 235) I had to fiddle with the pressure to keep it from sliding around in crosswinds, and the /forums/images/graemlins/k5.gif is a bit squidgy on corners now, so it's time to play ... /forums/images/graemlins/smile.gif

    -- A
     
  2. Greg72

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

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    Aaron,

    The chalk technique can work.

    Or just read the sidewall for "maximum pressure @ max load" and figure out a correction factor for the pressure based on the actual weight on the tire.

    My swampers are rated at something like 2600 Lbs @ 30 psi....since I know my truck is only pushing down at around 1250 Lbs per wheel, I run close to 15 psi on the street.

    Lower pressures will increase treadpatch contact (and really increase rolling resistance, reduce MPG, etc) but may also increase sidewall "squirm" on the street.

    Sometimes it's better to increase the pressure to get a "crisper" response of the tires, even though absolute traction may be slightly less.

    The problem on Bias Ply tires like my Swampers is that if you get too aggressive with the pressure (too much) you end up riding on the center lugs only....and they wear out before the outer lugs even have noticeable wear. IMHO, most people with big tires seem to run too much air pressure....
     
  3. dremu

    dremu Officious Thread Derailer Premium Member

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    Yeah, I'm thinking they're a bit lower than they should be from the squirm -- the /forums/images/graemlins/burb.gif did the same thing. I know that the wider tire will make her a bit harder to steer -- but the tires I had were shot, and these were no ca$h out of pocket, so I couldn't pass them up! /forums/images/graemlins/smile.gif

    Flipside is I know whatcha mean about overinflating though ... my 300ZX went through a set of rears that way. Expen$ive le$$on that was!
     
  4. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    I made this post about a week ago. I have been playing with it and it seems to work really well. The only problem with it is you need to repeat the test till you figure the correct pressure out at about the same outside temperature. The test will chage a little it it's 50deg in the morning at 75 in the afternoon.
     
  5. Shaggy

    Shaggy 3/4 ton status

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    <font color="green"> Grim, probably a stupid question, but is that test valid for both Bias and Radial tires? </font>
     
  6. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    Should be. It works on the premiss that the heat is created by the side wall flexing. If the tire has too little air then the side wall is flexing to much.
     
  7. wrathORC

    wrathORC 1/2 ton status

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    I go by sidewall squish. The tires should squish just a little so the all the tire hits the asphalt. Depending on how stiff the tire is as to what pressure I run. With 235x75r15 winter tires I ran 36 in the front and 34 in the rear. With my 31x10.50s I ran 33/28. With my street 33x12.50s I run 33/30. With my mud 33x12.50s I run 31/26.
     
  8. GMCLegacy

    GMCLegacy 1/2 ton status

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    wrath,
    are there any positions open in your tire changing pit crew? holy wah, you have more sets of tires than there are wheelin weekends this spring!

    taker easy
     
  9. wrathORC

    wrathORC 1/2 ton status

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    What'd you do, see me changing them again today? I used to have another set until relatively recently but they were p-metric and only 30" tall so I sold them to a local high school kid.

    Yeah, I know, I haven't gone yet this spring. Last time I wanted to go Tim was supposed to send an email but he waited until it was too late for me to go. Hopefully something is going on this weekend?

    see you at the meeting
     
  10. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    [ QUOTE ]
    wrath,
    are there any positions open in your tire changing pit crew? holy wah, you have more sets of tires than there are wheelin weekends this spring!

    taker easy

    [/ QUOTE ]
    Hahahaha Spring in MI hahahahaha now that's funny. I have had to wear a winter coat on Cass lake at a 4th of July party LOL.
     
  11. Executioner

    Executioner 1/2 ton status

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    Temp. Ft. Walton Beach Fl. home=Tucson, Az.
    Its going to be a Hot Summer, because I have brought the
    Az. heat with me.
     
  12. dremu

    dremu Officious Thread Derailer Premium Member

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    Damn, Grim, I almost always read your stuff ... my bad!

    And obtw thanks! /forums/images/graemlins/smile.gif

    -- A
     

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