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  1. #1
    Super Member HellaBroke's Avatar
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    Tires and tire pressures

    So long story short side walll blew out on my wifes kia... ordered 4 new michelin pilot sport a/s3 tires.
    Factory tires 215/55-17 pressures front and rear per door pannel is 33psi
    Front axle weight gvrw is 2425
    Rear axle weight gvrw is 2116
    Total 4299 gvrw
    New tires are 245/50-17 where can I go to figure out required pressures for new tires? Dealer had no idea...
    "No free man shall ever be debarred the use of arms. The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government" Thomas Jefferson,

  2. #2
    Super Member dpk20x's Avatar
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    I would check with Michelin.

    Sometimes the recommended PSI is even labeled on the tire.

  3. #3
    Super Member jgg85234's Avatar
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    Re: Tires and tire pressures

    There is no required pressure, and when you change the tire/wheel size there's not any set formulas that I've ever seen.

    Every tire manufactured has a maximum rating stamped into the side wall. You should never exceed that number.

    Tires can run their entire life at that pressure without problems. But, the car will ride very hard. You'll get maximum mileage out of those tires, but you'll pay for it on every pebble in the road.

    The suggested maximum set by the car manufacturer is a compromise based on maximizing tire mileage with a comfortable ride.

    I'd start with the 33psi setting. If you go below that setting, you'll find the tires wearing out on the edges faster than in the center.

    If you want to experiment, bump it up a few PSI at a time, until the ride is too harsh for your taste. But, don't exceed that maximum on the tire itself.

    Every pound of increased pressure will get you more mileage, better handling, less flex (and heat) on the sidewalls.

    Set the pressure with a good quality gauge (no pencil type gauges) when the vehicle has been setting for at least 3 hours, and not in the sun.

    Jim

  4. #4
    Super Member HellaBroke's Avatar
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    Re: Tires and tire pressures

    the answer i was looking for was 26psi ( not that i will run 26psi...)
    the factory kumhos needed 30psi minimum to support the weight of the car... the new michilins only need 26 psi to support the weight... handling will be garbage at 26 however the gain in load rating and minimum pressure being a full 4psi less should get me away from blowing a side wall from overloading again...

    something to look at when everyone changes tires from factory sized... stamp in the door jam is a good rule of thumb however not always what is best for the new sized tire and possibly rim.

    the Chalk trick is another really good way to figure out tire pressure...
    cover a 2" wide band of chalk across the tread and run the car forward and backwards total of around 25' in as straight of a line as possible play with tire pressure up and down until an even wear of chalk is worn from the tires...
    chalk trick isnt a scientific/mathmatical formula that i normally like to use however it has worked in the past when fine tuning and hasnt let me down.. mostly was looking for a new tip/trick
    "No free man shall ever be debarred the use of arms. The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government" Thomas Jefferson,

  5. #5
    Super Member FUNX650's Avatar
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    Re: Tires and tire pressures

    Glad no one was hurt due to the blowout.

    Also: I'm glad you figured out your new tires' inflation-psi...and Thanks for the chalk-tip!

    It's also pretty nice to know that your new tires:
    -Will take 9.62 less revolutions to travel one mile
    -Will allow your vehicle to use 1.27% less fuel
    -Will cause your vehicle's: "Speed" to be 1.27% more than the speedometer's
    'read-out' showed when the original tires were in use.



    Bob
    "Be wary of the man who urges an action in which he himself incurs no risk."
    ~Joaquin de Setanti

  6. #6
    Junior Member hellfst's Avatar
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    Re: Tires and tire pressures

    Quote Originally Posted by HellaBroke View Post
    the answer i was looking for was 26psi ( not that i will run 26psi...)
    the factory kumhos needed 30psi minimum to support the weight of the car... the new michilins only need 26 psi to support the weight... handling will be garbage at 26 however the gain in load rating and minimum pressure being a full 4psi less should get me away from blowing a side wall from overloading again...

    something to look at when everyone changes tires from factory sized... stamp in the door jam is a good rule of thumb however not always what is best for the new sized tire and possibly rim.

    the Chalk trick is another really good way to figure out tire pressure...
    cover a 2" wide band of chalk across the tread and run the car forward and backwards total of around 25' in as straight of a line as possible play with tire pressure up and down until an even wear of chalk is worn from the tires...
    chalk trick isnt a scientific/mathmatical formula that i normally like to use however it has worked in the past when fine tuning and hasnt let me down.. mostly was looking for a new tip/trick
    Not to flame you or anything, but did you inflate the tires yourself?
    In order to measure the psi in a wheel, the vehicle has had to be siting overnight or for a good amount of time so the tires can cool down. The ideal temp has to be 75 degrees outside. I don't remember exact psi, but you are around there. If you are keeping stock, the psi on the door jambs should tell you.

    I don't know why you thought the 26psi, they perform test on the tires before they let them go into the public. Rubber expands and retracts all the time, specially during climate changes. The only time you should add a little more psi is in the winter.

  7. #7
    Regular Member jamesalanb's Avatar
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    Re: Tires and tire pressures

    So you put more than an inch additional width and more than an inch worth of tire height on your wife's car, after over inflating the tires and causing a blow out? Did you do this research and decide a 245/50 was a good idea or did the dealer recommend this size to you? I'm not trying to be a jerk, but you will factually see zero increase in vehicle handling, not to mention the speedometer and odometer that were calibrated to a particular size tire height+/- a specific tolerance is now off. I'm all for aesthetics too, but huh. I'm just looking at your situation from the outside in...

  8. #8
    Super Member geekdout's Avatar
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    Re: Tires and tire pressures

    Going from a Kumho tire to pretty much the best tires on the road now, Michelin. Is normally a big upgrade in itself ride quality and overall road noise reduction are the two most noticeable. But now I would be concerned about rubbing on the fenders after taking big bumps. Also if you car is all wheel drive do not drive very far with a spare tire on, different size tires can cause driveline problems. Best of luck to you

  9. #9
    Newbie Member Sleypr's Avatar
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    Re: Tires and tire pressures

    You will need to test and tune as you drive. Always start at the OEM inflation spec for the car. The max pressure rating on the tire is the most pressure you can put in to push the tire to its max load capacity. Keep in mind a larger tire has a larger air volume, so less pressure is needed to support the same amount of weight. I went from a 215/55r17 to a 245/45r18 on my G35 and dropped from 35psi stock to 32psi to stop the crack slap on our roads.

  10. #10
    Newbie Member Sleypr's Avatar
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    Re: Tires and tire pressures

    Quote Originally Posted by FUNX725 View Post


    -Will allow your vehicle to use 1.27% less fuel


    Bob
    Not entirely true, the added width and diameter of the tire will add unsprung weight. Also increasing the tires rolling resistance using more power to get down the road.

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