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What psi should i run?

Discussion in 'Wheels & Tires' started by TacoTRD420, Sep 10, 2009.

  1. Jul 8, 2020 at 5:40 PM
    #281
    splitbolt

    splitbolt Well-Known Member

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    Stock tire is a 265/70/16/112; @ 30 psi it has a load capacity of 2,149 lbs.
    Euro metric and P metric tires are de-rated for use on trucks and SUVs. When you switch to an LT, you need a psi that attains a 1,954 lb load capacity...2,149÷1.1=1,954
    A LT265/75/16 has a load capacity of 1,986 lbs @ 37 psi.

    Air down pressure depends on terrain and speed. Generally, you don't start getting the benefits of airing down until 20 psi or below. Experiment...
     
    emonomics likes this.
  2. Jul 8, 2020 at 7:48 PM
    #282
    emonomics

    emonomics Well-Known Member

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    Thank you!
     
  3. Jul 13, 2020 at 2:01 PM
    #283
    yourrealdad

    yourrealdad Well-Known Member

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    Can I play this long running game?

    Got new LT265/75/R16 Wildpeak AT3W on. Sneaky lil shop boys had them aired up to 42psi front and 44psi rear.

    I just chalk tested warm (1pm, but not driven)

    I am now at 34psi front and 30psi rear

    I am stock no extra weight
     
  4. Jul 13, 2020 at 2:07 PM
    #284
    yaaj2005

    yaaj2005 Well-Known Member

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    I will chip in too.... Currently running 295/75/16 BFG KO2... Running 30 psi all around for ride comfort.
    FYI. Every truck set up is different. Example, front bumper, winch, skid, slider, camper shell, constant weight on bed and etc... will determine what psi you are running. So there is no set psi, one will have to determine that them self. What work for you, might not for other...
     
    Island Cruiser likes this.
  5. Jul 13, 2020 at 5:27 PM
    #285
    splitbolt

    splitbolt Well-Known Member

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    With an LT295/75/16 @ 30 PSI, you are at 2,020 lbs load capacity...the formula method requires 1,954 lbs load capacity. So, you're real close...
    With LTs, generally, the larger the tire volume the less psi is required for the same load capacity.

    I dislike the chalk method...
    -it's a holdover from the days of bias plies; modern radials do not react the same
    -doesn't account for dynamic loading of the tire
    -doesn't account for mounting on a non-nominal rim width, which changes tire section width; chalk footprint expectations do not change
    -conditions to do a proper chalk method are difficult, if not impossible to replicate
    -according to purveyors of the chalk method...loading 3 adults or any significant load requires re-chalking
     
    Last edited: Jul 13, 2020
    yaaj2005 and Greg.Brakes.Tacos like this.
  6. Jul 13, 2020 at 7:02 PM
    #286
    yaaj2005

    yaaj2005 Well-Known Member

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    You are right....:thumbsup::thumbsup::thumbsup::thumbsup::thumbsup:
     
  7. Jul 14, 2020 at 4:30 AM
    #287
    Pete_Patter

    Pete_Patter Well-Known Member

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    I am going to bring up a fact that most people dont consider. Toyota doesnt set the door placard psi only for load rating. They do it for ride comfort and fuel economy since the tires are always larger than they need to be for load carrying capacity of the vehicle. So while it is safe to use this to calculate to different size tires you will always end up wth too high of a psi when converting from SUV (p-metric) to LT tires. So you need to look at the Gross Vehicle Weight Rating (GVWR) which if you are looking at a 3rd gen is 5600lb then you divided by 4 to get 1400lb per tire minimun. From there you can figure out your minimun pressure based on your new tires size. But this minimum psi is not going to end up with the best ride charactersitics and you will need to adjust to get the proper contact patch. With all of this in mind I think the chalk test is a great starting point.
     
  8. Jul 14, 2020 at 4:48 AM
    #288
    splitbolt

    splitbolt Well-Known Member

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    Inflating for mpg and ride comfort seem contradictory, no?

    It's GVWR x dynamic load & safety factor = inflated load capacity

    The placard has a 2,149 lb load inflation for P and Euro metric tires. This translates to 1,954 lbs load inflation when an LT is used.

    Dynamic & safety load factors:
    1,400 x 1.54 = 2,156...P and Euro metric
    1,400 x 1.40 = 1,960...LT

    This is the load chart for a euro metric 112 SL; what comes on the Offroad and Pros.
    According to you, inflation psi would be below 22 psi. Notice the load capacity at the recommended 30 psi; 2,149 lbs.

    Screenshot_2020-07-14-07-08-04.jpg
     
    Last edited: Jul 14, 2020
    Greg.Brakes.Tacos likes this.
  9. Jul 14, 2020 at 5:07 AM
    #289
    Pete_Patter

    Pete_Patter Well-Known Member

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    It only seem contradictory if you consider that low tire pressure would not be comfortable driving then MPG/comfort work together.
    I think I missed where the 1.54 and 1.40 saftey factors came from? You may have said it before in the thread but I am sorry I missed it.

    I am not trying to say that your extra saftey factors are wrong I am just saying that if you have an LT tire I think that you will be over inflating it and it will be a harsher ride than you will need for Load.
     
  10. Jul 14, 2020 at 5:12 AM
    #290
    splitbolt

    splitbolt Well-Known Member

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    Check my edit...
     
  11. Jul 14, 2020 at 9:56 AM
    #291
    Pete_Patter

    Pete_Patter Well-Known Member

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    Sorry I understand how the chart works it is taken from the "ETRTO manual" which is for european tires. I am just trying to understand where the Dynamic & safety load factors (1.54 and 1.4) came from? I am pretty possitive that those load values are dynamic load conditions.

    I am not suggesting that you run your OE tires at 22psi but you could run the tires on your vehicle at 22 psi with the tire having issues. Although You wouldnt want to do this for the lifetime of the tire.
    I am not stating to run at minimum pressure what I am stating is that when you convert SUV to LT tires they are not created equal thats why I am trying to understand where your saftey factors came from.

    I think the confusion is coming from that fact that you are trying to use the placard psi to determin the load that the tires need to be and I am trying to say they dont need to handle that much load. They are putting the tire pressure that high for handling, mpg, and comfort.

    Take a look at the sticker to the right of the placard it says Front Gross Axle weight is 2,755 lb or 1,377.5 lbs per tire. Rear gross axle is 3,110 lb or 1,555 lb per tire. This is the most weight you should put on the front and rear axle.

    [​IMG]
     
    Last edited: Jul 14, 2020
  12. Jul 14, 2020 at 10:29 AM
    #292
    splitbolt

    splitbolt Well-Known Member

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    You're saying inflate to GVWR...or 1,400 lbs at each tire.

    The stock tire(a euro metric 265/70/16/112) at it's recommended 30 psi is 2,149 lbs of load capacity...
    2,149÷1,400=1.54

    An LT only requires 1,954 lbs load inflation because euro and P metric tires are de-rated for use on suv/trucks.
    2,149÷1.1=1,954
    1,954÷1,400=1.40

    If you want to disregard it for the reasons you mention...I'm not going to try to convince you otherwise. But, there it is.
     
  13. Jul 14, 2020 at 10:52 AM
    #293
    Pete_Patter

    Pete_Patter Well-Known Member

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    I am not say to inflate to GVWR or GAWR because this would not be a very good footprint or ride. I am saying that it is safe and you dont need the 2,149lb that comes with the vehicle.
    Toyota isnt trying to get 2,149lb of load capacity. That value is just what came out once Toyota got the right footprint and response of the tire. Also you shouldnt load the front axle past 2755 lb and the rear axle past 3110 lbs. I am just trying to work through the facts so that people arent overloading their LT size tires and then saying that they are super stiff and uncomfortable because they are trying to meet a load that they dont need.

    You can continue to do it the way you have been and be safe.
     
    Last edited: Jul 14, 2020
  14. Jul 14, 2020 at 11:22 AM
    #294
    yourrealdad

    yourrealdad Well-Known Member

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    I drove the truck around. It rode better, was more comfortable, quieter, and people were rubber necking because I looked so cool with my tires at 34/30.
    Also I didn't make my chalk test perfect, because it was mid day and the tires will cool off, also once they get heated up I figure they will gains some PSI and that can counteract any additional common loads (aka SWMBO).

    If it is winter or hauling I will add some PSI, if I am off roading then I will decrease it.

    In the meantime I rotate every 5k and won't worry too much
     
    Bamadrifter likes this.
  15. Aug 1, 2020 at 2:00 PM
    #295
    Bamadrifter

    Bamadrifter Cat wrangler and quesadilla chef

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    Wow, this tutorial/sticky is creeping up on 11 years old. After a thorough skimming of stuff from Chris and his chalk, plus the more recent analysis from Pete & Split I have decided 32psi all round, or 34 in front and 32 in rear is what my ideal pressures will be. That of course depends on the lazy factor and how I have about a dozen other things to do before fixing my air pressure. Anyway, really neat info here. Thanks for all the input from everyone! :hattip:
     
  16. Aug 2, 2020 at 10:00 PM
    #296
    gusto11071

    gusto11071 Well-Known Member

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    TPMS Universal.jpg
    This is going to be my monitor, LoL
     
  17. Aug 3, 2020 at 6:08 PM
    #297
    Bamadrifter

    Bamadrifter Cat wrangler and quesadilla chef

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    Status update: Made a point to check my pressure this afternoon and (w/ the Alabama heat) I'm 35 front/ 34 rear. No way to easily fix my TPMS light until I go back to stock rims & etc. but am glad my tires are good now. This was my first check since buying the truck a week ago. Maybe the service tech is a TW lurker. ;)
     
  18. Sep 1, 2020 at 6:34 PM
    #298
    4x4cajun

    4x4cajun Well-Known Member

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    CHEVERLY my service dog! Lol
    I don’t know about anyone else but if I run rear tires over 35 psi my backend spins when taking turns from a stop. I’m running 18’s on my 4x4 Limited DCLB. Pretty much 32 all around but I don’t carry much ..
     
  19. Jan 2, 2021 at 8:15 AM
    #299
    along16

    along16 Well-Known Member

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