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Thread: different size tires

  1. #1
    Join Date
    Nov 2012
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    1991 535, 1986 524td

    different size tires

    I have 2 questions about the size of tires on my e83 from 3/2004.
    In front size is 235/50 - 18, in the rear size is 255/45 - 18.
    Was this a mistake of the former owner, or is this usual?? If I look in "will they fit" the difference in size is not big, so in my opinion not to big of problem.

    Since these tires are summertires, I will change them upcoming winter for all seasons. My other question is, What is the size of tires to choose to have the wheel openings better filled???
    I know my speedometer will not be accurate, but in this setup it shows a speed which is 8 percent faster than GPS speed.

    any help is appreciated

  2. #2
    Join Date
    Oct 2016
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    Georgia - USA
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    2009 X3
    This is something I am familiar with as I just went through this issue myself. Your E83 is an AWD vehicle so it is very important the tires are the same over all diameter or you will cause damage to your transfer case and/or transmission. The transfer case can handle a 1% difference in overall diameter from front to back.

    I notice that in the tires sizes mentioned above, the aspect ratio's are different which may mean the previous owner was aware the tires needed to be same diameter (-+1%). I suggest going to tire rack and looking o the tires you have and review the specs for the tire diameters to confirm if they are ok or not.

    I suspect that you are OK or else you would be complaining of other issues such as a vibration or shuddering under load or acceleration.

    Verify your tire diameters and post back and let us know what you find out. Like I say I had this problem and posted about it. Look for my post on "Drive Line Vibration" if you would like.

  3. #3
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    Thanx Iroman3
    Our X3 is an AWD, and according "will they fit.com", the difference between front and rear is 0.79%, so in tolerance of the given 1%.
    What tire size do you suggest to fill up the empty space between body and tire???

  4. #4
    richardodn's Avatar
    richardodn is offline Old Guy BMW CCA Member
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    You have what is called a staggered setup. Typically, the front and rear wheel widths are different. The 235/50/18 front & 255/45/18 rear was a factory fitment in 2004. They were put on 8Jx18 ET46 and 9Jx18 ET51 wheels respectively.

    To fill up the empty space you're going to need larger overall diameter tires. This will affect your speedometer readings resulting in you going faster that your speedometer reads. I don't know of any way to correct that.
    Last edited by richardodn; 06-21-2020 at 07:25 AM.
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  5. #5
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    Thanks richardodn. I did not know that, now it makes sense. The speedo is 5 percent off. Speedo says 100kmh, gps says 95 kmh. So i will choose tires with 5 percent bigger circumference, to get me in the ballpark.

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