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Thread: Proper tire pressure

  1. #1
    resident Humboldt's Avatar
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    Proper tire pressure

    Some sites say to go by what's printed on the vehicle placard, others say this should only be used when the car is new with standard tires and to otherwise go with what's stamped on the tire itself.

    Isn't this the max cold pressure though, which might be different from the manufacturer's recommended specs?

    My Pathfinder feels sluggish if I use what's posted on the placard.

  2. #2
    Regular Member BroncoSport's Avatar
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    You should inflate your tires to what the TIRES say on the sidewalls. Your vehicle (unless you have a expensive luxury vehicle) do not "have to" have a specific brand or ply rating of tire. Different brand tires may have different requirements. The higher "ply rating" you get the more air is required in the tire. Along with that, the more air pressure the rougher the ride.

    for example pickup trucks on a farm might have 10 ply tires. They are less prone to flats but ride rough. Air pressure could be around 80 psi.

    a street truck would have normal passenger tires with 4 to 6 plys. good ride but not as "tough" as the higher ply rating. Normal reception to flats. Air pressure around 35 to 40 psi.
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  3. #3
    Auto Tech joecool169's Avatar
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    Actually you should inflate the tires to what it says on the door. The manufacturer specs the tire pressure when they design the vehicle.
    Joe

  4. #4
    resident Humboldt's Avatar
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    See what I mean?
    Two opinions, both seem valid.
    I understand that the tires I have now might be and probably are different from the exact manufacturer specs. I think it came with street tires and I have some light truck tires on it now. Not super offroad but a couple steps up from a straight street tire, thicker treads and overall a bit larger. Chances are they need to be inflated to a higher psi than what the vehicle originally came with.

    But many sites say to go with the placard ratings.
    When I've set the tires to that psi though they just look kinda flat and the ride is slow and mushy as hell, worse than trini's mom even.

  5. #5
    Junior Member MadDoctor's Avatar
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    I go by what the guy at the gas station says because he has a uniform on. Ok... a hat with a logo.

    *edit*


    Wait?!?!?!?! WTH?!?!?!?!?! Who put that picture in without my permission???????

    People will forget what you said... and people will forget what you did... but people will never forget how you made them feel.

  6. #6
    NYC Newbie Slayer Prey521's Avatar
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    Quote Originally Posted by Humboldt View Post
    Some sites say to go by what's printed on the vehicle placard, others say this should only be used when the car is new with standard tires and to otherwise go with what's stamped on the tire itself.

    Isn't this the max cold pressure though, which might be different from the manufacturer's recommended specs?

    My Pathfinder feels sluggish if I use what's posted on the placard.
    I set my trucks tires to 40 all around. I go by what's on the sidewall of my tires, not the door jam.
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  7. #7
    SG Enthusiast Leatherneck's Avatar
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    The tire itself just lists a "maximum" pressure and should not be used in all applications. They don't print the recommended pressure on the manufacturer's placard for nothing. If they are not the original tires then a little logical thinking is in order, but 45psi like many maximums is usually not at all necessary. I usually split the difference between the two when I'm not sure.
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  8. #8
    resident Humboldt's Avatar
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    *waits for the other dumb bastard from NC to chime in*

  9. #9
    Token Dial-up User De Plano's Avatar
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    I had mine at fifty (it says 65 on the side wall) and the guy at Les Scwab dropped them down to 40. Said I would get uneven wear at that high of PSI

  10. #10
    resident plumber Mark's Avatar
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    Quote Originally Posted by BroncoSport View Post
    You should inflate your tires to what the TIRES say on the sidewalls. Your vehicle (unless you have a expensive luxury vehicle) do not "have to" have a specific brand or ply rating of tire. Different brand tires may have different requirements. The higher "ply rating" you get the more air is required in the tire. Along with that, the more air pressure the rougher the ride.

    for example pickup trucks on a farm might have 10 ply tires. They are less prone to flats but ride rough. Air pressure could be around 80 psi.

    a street truck would have normal passenger tires with 4 to 6 plys. good ride but not as "tough" as the higher ply rating. Normal reception to flats. Air pressure around 35 to 40 psi.
    i do this, i set them to max recommended by what the tire says.

  11. #11
    Second Most EVIL YARDofSTUF's Avatar
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    I just fill it so it looks right.

  12. #12
    resident plumber Mark's Avatar
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    Quote Originally Posted by YARDofSTUF View Post
    I just fill it so it looks right.
    you don't use a good tire gauge ?


  13. #13
    Second Most EVIL YARDofSTUF's Avatar
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    Quote Originally Posted by Mark View Post
    you don't use a good tire gauge ?

    Ya I do use a gauge. lol

  14. #14
    Moderator YeOldeStonecat's Avatar
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    What's on the car by the manufacturer. To back up this statement...
    http://www.drivers.com/article/354/
    http://autopedia.com/TireSchool/pressure.html
    http://www.nhtsa.dot.gov/cars/rules/.../brochure.html

    They design the car based on that. Tires just tell you what maximum pressure the tire is rated for...which is generally always higher than what the cars maker designed the car on. But if you're changed aftermarket tires that have a maximum PSI rating that is lower than what your cars manufacturer tells you..well..first of all, exchange the tires..you bought the wrong ones for your car. But if you're stuck with them..obviously you want to not inflate them higher than what they're rated for.

    Checking tire inflation...remember, it changes from cold to warm, as you drive, winter/summer, etc. Remember..things expand as they warm. So measuring your tire pressure when the tires are cold...you'll get one reading. Go drive down the highway for 1/2 an hour..and measure them again. See anything different? Yeah...the reading went up...quite a bit. So taking the fact into consideration...say you need to inflate your tires to 36psi, and you do this when they're cold...and you go drive down the highway, things get warm inside, expand, and sure enough your tire pressure is now too high (something like 38 or 40psi). Depending on size of tire, climate, etc....every 10 degrees of temp rise or fall will change PSI by 1-2 PSI..depending on size of tire. So if your only opportunity to inflate your tires is when they're cold..inflate them to a PSI or two below the rating. Example..say they're rated for 32PSI, inflate to approx 30. As they heat up, they will approach and/or hit 32PSI.
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    Dr Tweak mnosteele52's Avatar
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    My mechanic, a good friend, recommends 35psi.

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  16. #16
    resident plumber Mark's Avatar
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    Quote Originally Posted by mnosteele52 View Post
    My mechanic, a good friend, recommends 35psi.

    what about my 1 ton work van, the tires are rated for 70PSI i think

  17. #17
    NYC Newbie Slayer Prey521's Avatar
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    A buddy of mine has his tires filled with Nitrogen I believe and he says that he hasn't had to adjust the pressure in almost a year. He checks it every month.
    Have your feelings been hurt by a random act of E-Thuggery? If so, call 1-800-Waaaaahmbulance, we're here 24 hrs a day, 7 days a week, to take your call, you could be due a large monetary settlement, don't delay, call now.

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  18. #18
    Regular Member BroncoSport's Avatar
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    Quote Originally Posted by joecool169 View Post
    Actually you should inflate the tires to what it says on the door. The manufacturer specs the tire pressure when they design the vehicle.
    Yeah the for the tires it rolled out of the factory with. But unless you put the exact brand and model and SIZE of tire back on the vehicle then the pressure is dictated by the make of tire. Most autos are 35psi, as are trucks but farm trucks and semi...are 80-90 and believe me that the door sticker on MY truck isnt acurate. This truck was bought as a cab only and now weighs 20,000 lbs. Rides pretty rough but if I put the 45 psi marked on the door in my tires, I would ruin 6 tires.
    I know you are, but what am I?

  19. #19
    Auto Tech joecool169's Avatar
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    Quote Originally Posted by BroncoSport View Post
    Yeah the for the tires it rolled out of the factory with. But unless you put the exact brand and model and SIZE of tire back on the vehicle then the pressure is dictated by the make of tire. Most autos are 35psi, as are trucks but farm trucks and semi...are 80-90 and believe me that the door sticker on MY truck isnt acurate. This truck was bought as a cab only and now weighs 20,000 lbs. Rides pretty rough but if I put the 45 psi marked on the door in my tires, I would ruin 6 tires.
    And cab only should get an updated tag in the door jamb by the manufacturer of the bed.

    I am an ASE certified master technician with a lot of experience. I did not just make this answer up. I answered correctly. If you do something different with your vehicle or your tires than that is fine. If you want to voice your opinion no one is stopping you. I simply supplied the correct answer to his question.

    If you have a pickup truck and you put the same size tire, and load range then the door jamb tag will be correct. If you switch load range, which technically you should not, then that is a different story.
    Joe

  20. #20
    Auto Tech joecool169's Avatar
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    Quote Originally Posted by YeOldeStonecat View Post
    What's on the car by the manufacturer. To back up this statement...
    http://www.drivers.com/article/354/
    http://autopedia.com/TireSchool/pressure.html
    http://www.nhtsa.dot.gov/cars/rules/.../brochure.html

    They design the car based on that. Tires just tell you what maximum pressure the tire is rated for...which is generally always higher than what the cars maker designed the car on. But if you're changed aftermarket tires that have a maximum PSI rating that is lower than what your cars manufacturer tells you..well..first of all, exchange the tires..you bought the wrong ones for your car. But if you're stuck with them..obviously you want to not inflate them higher than what they're rated for.

    Checking tire inflation...remember, it changes from cold to warm, as you drive, winter/summer, etc. Remember..things expand as they warm. So measuring your tire pressure when the tires are cold...you'll get one reading. Go drive down the highway for 1/2 an hour..and measure them again. See anything different? Yeah...the reading went up...quite a bit. So taking the fact into consideration...say you need to inflate your tires to 36psi, and you do this when they're cold...and you go drive down the highway, things get warm inside, expand, and sure enough your tire pressure is now too high (something like 38 or 40psi). Depending on size of tire, climate, etc....every 10 degrees of temp rise or fall will change PSI by 1-2 PSI..depending on size of tire. So if your only opportunity to inflate your tires is when they're cold..inflate them to a PSI or two below the rating. Example..say they're rated for 32PSI, inflate to approx 30. As they heat up, they will approach and/or hit 32PSI.
    Very nice reply. But do note that most manufacturers recommended pressure is cold.

    On a side note, Nascar tires can expand like 40PSI from heat.
    Joe

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