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Wheel Upgrade - Offset

Discussion in 'Wheels & Tires' started by 391075, Apr 20, 2014.

    • Member

    391075

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    I would like to upgrade the wheels on my 2008 X3 (E83) . The purpose is to use the stock wheels for snow tires next winter. The car came equipped with 17 x 8 wheels with a 5 x120 bolt pattern and 46mm offset. The tires are 235/55 x 17. My hope is to use a stock wheel (18 x 8, 5 x 120 bolt pattern) from a more recent X3 however I noticed the newer wheels have a 43mm offset. Are the wheels interchangeable ?? I am also hoping that installing 235/50 x 18 tires as offered as an option in 2008 will not effect the accuracy of my speedometer/odometer.
    Advice appreciated.
    • Member

    MGarrison

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    Offset can vary with wheel width - relatively speaking though, _all else being equal_, it's hard to imagine a 3mm difference would be likely to cause a clearance issue.

    The wheels need the same hub diameter also, or else you'd need hub rings or adapters. Look at overall diameter to assess impact on speedometer accuracy.

    http://www.1010tires.com/Tools/Tire-Size-Calculator

    You can read-up here on offset, centerbore, plus-sizing, etc:

    http://www.tirerack.com/wheels/tech/index.jsp

    http://www.tirerack.com/tires/tiretech/tiretech.jsp

    Tire rack shows the alternate size you mention, I don't find it exactly clear that using that size might not affect speedometer accuracy. If your original size is 235/55-17, typical plus sizing to keep close to rolling diameter, you'd go for a 245/45-18. Use the 1010 size calculator to compare 235/55-17 & 235/50-18; since they're the same width & you get 1" more overall dia. from the larger dia. wheel, I'm not sure a 50 aspect ratio is enough to keep you at same overall diameter (although, it may be a relatively insignificant difference). Seems to me the speedo might be calibrated to one, or the the other - if both sizes were offered by BMW for your model at the time, then presumably, you have to guess that BMW had some speedo calibration that they deemed was good enough for either wheel/tire combination. Unless there's someway for the car to know what size it's running - sensor... spec to set someplace... I'm guessing unlikely, though.

    By the same token, if your overall diameter is within a range that's safe to run, and you understand the effects on your speedometer accuracy, considering that BMW speedometers are typically optimistic anyway, concern over speedo accuracy might be less of an issue, and you opt to run what you want anyway.

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