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  1. #1
    Join Date
    Oct 2012
    Location
    California
    Posts
    100

    Default Best way to tell if I have a 286 or 305mm size rotor..

    I have tried measuring the disk by taking the tire off, but it is hard to tell because of the bulkiness of the rotor. I have had to measure with a string, but the center is raised and bulky, so I cannot get a correct measurement. The .75 inch difference or 20mm, has been difficult.

    What would be the best way without actually taking the rotor off?
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  2. #2
    Join Date
    Jul 2013
    Location
    alabama
    Posts
    51

    Default

    20 mm is 2 cm so it can't be that hard to tell. and the best way to measure IS to take the rotor off, then measure from the back side.

  3. #3
    Join Date
    Oct 2012
    Location
    Decatur, TN
    Posts
    84

    Default

    I measured mine quite easily with just the tire off, it is quite obvious if it is 286 or 305. You can lay 2 straight edges on the rotor edges and measure the distance between them.
    2002 V70XC 260k+ miles

  4. #4
    Join Date
    Feb 2012
    Location
    California
    Posts
    418

    Default

    Put a clamp type thing on the sides of the rotor to extend a measurement device and then take the measurement. Not sure if that made sense.
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  5. #5
    Join Date
    Sep 2013
    Location
    Netherlands
    Posts
    1

    Default

    By using a thin rope around the circumference of the disk?

    Circumference [mm]/3.14 (pi) = diameter

  6. #6
    Join Date
    Feb 2011
    Location
    Windy Manitoba
    Posts
    628

    Default

    Remove wheel. Set up surveyor's transit some distance from the car. Use transit to measure angle between two sides of the rotor and distance from transit to brake rotor. High school trigonometry will tell you the width of the rotor.

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