Proper tire pressure question....
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2004-2007 Cadillac CTS-V General Discussion Discussion, Proper tire pressure question.... in Cadillac CTS-V Series Forum - 2004 - 2007; Should I be using the OEM tire pressure recommendations on the sticker on my door jam? I went from a ...
  1. #1
    kimcheejeegae's Avatar
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    Proper tire pressure question....

    Should I be using the OEM tire pressure recommendations on the sticker on my door jam?

    I went from a 245/45-18 stock to 255/45-18.... and since my new tires are not runflats, shouldn't I be running "more" pressure than I did with the runflats?

    On my previous cars, I ran 36-38 all the way around on 255/35/19s.....

    BTW... My tires are at 40 psi right now.... and everytime one tire hits 42psi or more, the freaking TPS alarm goes off... annoying!!

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    ctsvett's Avatar
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    Re: Proper tire pressure question....

    Recommended COLD tire pressure is 30 psi...

    Reed

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    Texan V's Avatar
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    Re: Proper tire pressure question....

    Mine typically start around 30 -31 and warm up to 34 - 35.


    Toyo's BTW...

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    Re: Proper tire pressure question....

    OEM Recomendations are for OEM tires, ask who ever installed your tires what their proper cold PSI should be, different tires, different settings.

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    Re: Proper tire pressure question....

    Everything I have read says that the vehicle placard shows the correct tire pressure for the tires (not matter what brand tire). Tire pressure is related to the load rating of the vehicle.

    Our recommended cold PSI from GM is 30 psi cold... I believe (and I am no expert here) that aftermarket tires should also be inflated to 30 psi cold.

    from 101tires.com: "Even if the tires have been changed since the vehicle was new, the car manufacturers recommended pressures still apply. "

    The only factor that is leading me to question this logic is if you are going from runflats (with higher sidewall stiffness) to non runflats (with lower sidwall stiffness) MAY indicate that you should increase the psi on the non runflats a bit to compensate for the lack of sidewall stiffness...

    Anyone else here care to chime in?

    Reed

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    Post Re: Proper tire pressure question....

    When my tires are at 32psi the ride feels the best, so I leave them around 28-29psi cold.

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    Re: Proper tire pressure question....

    I recently purchased Toyo T1Rs and the dealer suggested 32psi when cold. That has worked well for me. They warme up to 36-37psi.

    CR

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    Re: Proper tire pressure question....

    Here is what the RMA (rubber manufacturers association) says:
    -------------
    ANSWERS
    1. The best place to find the recommended
    tire pressure for most vehicles’ tires
    is...
    (b) The vehicle owner’s manual or
    tire information placard.

    The tire information placard is a decal
    posted on the vehicle doorframe, glove
    box door, or fuel door. Like the owner’s
    manual, it tells the recommended tire
    pressure for the specific vehicle. The tire
    sidewall does NOT provide this information,
    listing instead the maximum allowable
    pressure for the specific tire.

    ----------------

    Dammit... I need a life...

    Reed

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    Re: Proper tire pressure question....

    For racing....
    ----------
    While most cars will utilize a similar tire pressure range, the difference of one psi will make a noticeable diffence in handling to even a moderately experienced driver. Two pounds can make a major difference in a car's overall grip level that even a novice can recognize. Therefore, asking what someone else uses for a tire pressure is completely irrelevent information (unless it's the exact same car setup). You must do the testing on your car to determine the optimum pressure setting for a given track and ambient conditions.

    -----------
    From : http://www.turnfast.com/tech_practic...ce_tires.shtml

    Reed

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    Re: Proper tire pressure question....

    With the switch to non-runflats, you will need more pressure to have your V handle in a similar manner. I will now refer to the "wheel rate" levels, not pressure.
    With a runflat, the sidewall stiffness will allow the tire to resist "squish" on turn-in and while turning. This force works in tandem with the spring to reach a certain "wheel rate", in other words, the force to compress the suspension (while driving) 1" could be ...and this is just an example...400lbs/inch.
    When you switch to a non-runflat, the tire will "squish" more at the same tire pressure because of the softer sidewall. This will lower the "wheel rate" to ...again just an example...of 380lbs/inch. The bad thing about this is that the tire is deforming more than intended, so if you are using the same size sidewall...you have a much higher chance of compressing the tire over...say...a pothole...and you could bend a rim, where the stock runflat would resist the compression. The lower wheel rate will also slow your transitions between turns and generally make the car "softer".

    My recommendation would be to run higher than stock pressures, notwithstanding the handling issue, just to add a little security to your wheels. The V was designed with runflats. The levels on the door and in the owners manual are not meant to be used on non-runflats.

    As it is, with runflats, I can't run the optimal pressures due to the TPS alarm. I'd run over 42 if I could, but keep it 40-41 on autoxes. When I switch to non-runflats, I'll need to somehow learn to live with the alarm or do away with them.

    Bottom line, you need to experiment as to what you like best...what works for you...and your wheels.

    Ve good,
    ace996

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    Re: Proper tire pressure question....

    Quote Originally Posted by ace996
    With the switch to non-runflats, you will need more pressure to have your V handle in a similar manner. I will now refer to the "wheel rate" levels, not pressure.
    With a runflat, the sidewall stiffness will allow the tire to resist "squish" on turn-in and while turning. This force works in tandem with the spring to reach a certain "wheel rate", in other words, the force to compress the suspension (while driving) 1" could be ...and this is just an example...400lbs/inch.
    When you switch to a non-runflat, the tire will "squish" more at the same tire pressure because of the softer sidewall. This will lower the "wheel rate" to ...again just an example...of 380lbs/inch. The bad thing about this is that the tire is deforming more than intended, so if you are using the same size sidewall...you have a much higher chance of compressing the tire over...say...a pothole...and you could bend a rim, where the stock runflat would resist the compression. The lower wheel rate will also slow your transitions between turns and generally make the car "softer".

    My recommendation would be to run higher than stock pressures, notwithstanding the handling issue, just to add a little security to your wheels. The V was designed with runflats. The levels on the door and in the owners manual are not meant to be used on non-runflats.

    As it is, with runflats, I can't run the optimal pressures due to the TPS alarm. I'd run over 42 if I could, but keep it 40-41 on autoxes. When I switch to non-runflats, I'll need to somehow learn to live with the alarm or do away with them.

    Bottom line, you need to experiment as to what you like best...what works for you...and your wheels.

    Ve good,
    ace996
    Very well said!! The Dunlops responded well to a bump in pressure to about 36lbs cold. I may even go higher. When I first got them on, I liked them but thought they folded over a little too easily and obviously were a little numb on initial turn-in compared to the runflats.

    Going on a long trip to Indy, I wanted to leave the pressures alone since they could creep up near 42lbs on long interstate runs in high heat. It was on that trip that I noticed how much better the Dunlops felt with higher pressures. I would start at 32 cold. On a fun rally, the V handled well but did have a numb turn-in with a lower g limit. One of the S/C SHO guys came up behind me all rallye like. So we followed each other down some remote backroads of Indiana. My tires got up to 42 and were much more responsive with higher limits.

    I may as well take out the sensors since I hit the alarm during any extended driving or "hot" sessions.

    On a side note, when I ran the Hoosiers at Putnam Park, the sensors kept getting picked up by the computer, at least that's what it read. Putnam is a 1.8 mile course and I'd say it's at least a mile from the furthest part of the track to the paddock area. Does the sensor have to lose contact for a period of time before it fails to read? Because the Hoosiers are sensor free. It was nice because I could still shut off the nanny.

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    Luna. is offline Cadillac Owners Connoisseur
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    Re: Proper tire pressure question....

    Quote Originally Posted by kimcheejeegae
    I went from a 245/45-18 stock to 255/45-18.... and since my new tires are not runflats, shouldn't I be running "more" pressure than I did with the runflats?
    This is mildly off-topic, so I apologize in advance, but did you go 255 all the way around? Do you recommend doing that without a doubt?

    Thanks for your thoughts

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    Re: Proper tire pressure question....

    Quote Originally Posted by Luna.
    This is mildly off-topic, so I apologize in advance, but did you go 255 all the way around? Do you recommend doing that without a doubt?

    Thanks for your thoughts

    Luna,

    I did go with 255/45/18s all the way around. I would like to stagger my tires only when I get rims for my car, and I'll actually stagger those.. 8.5s and 9.5s. The 255/45/18 is about 1.3% bigger in rolling diameter than the stock 245/45/18... I would have gone 255/40/18 (which are 2.4% smaller in rolling diameter)...but I wanted more sidewall since these are not runflats... they look so fat and juicy.. I'll post pics tonight. =)

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    Re: Proper tire pressure question....

    Please NO posting, See Red box at top of each page!

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    Re: Proper tire pressure question....

    Quote Originally Posted by benjet
    Please NO posting, See Red box at top of each page!
    We can post it will just be lost after the upgrade. For the people that doesn't bother...let the posting continue, right?

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