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Thread: Backspace and Offset, How do they relate?

  1. #1
    Advertiser Discount Tire's Avatar
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    Backspace and Offset, How do they relate?

    Offset and backspace are essentially two different ways of looking at the same thing. They determine the location of the wheel and tire assembly when bolted to the vehicles hub.

    Offset is the measured distance between the hub mounting surface and the wheels center line.

    With X being the determined offset, the hub mounting surface on positive offset wheels is X amount forward from the wheel center line. The hub mounting surface on negative offset wheels is X amount backwards from the wheel center line. The hub mounting surface on 0 offset wheels is the wheel center line.

    Backspacing is the measurement from the hub mounting surface to the back edge of the wheel.



    ***Typically speaking, the higher the offset/backspace, the more the wheel will tuck inwards towards the suspension or away from the fender. The lower the offset/backspace, the more the wheel will push out away from the suspension or towards the fender.

    For Example:

    *If the offset on a 9" wide wheel is +12mm, the hub mounting surface will be 12mm forward from the wheels center line. Measuring from the hub mounting surface to the back edge of the wheel, the backspacing is 5.5"

    *If the offset on a 9" wide wheel is -12mm, the hub mounting surface would be 12mm towards the back of the wheel from the wheels center line. Measuring from the hub mounting surface to the back edge of the wheel, the backspacing is 4.5"


    Here's how to calculate the backspacing using the rim width and offset:

    First - add 1" to the rim width and then divide by 2 to find the wheels center line (you have to account for the wheel flange which is why you add 1" to the rim width) . Second - convert the offset which is in millimeters into inches. There is 25.4mm in 1 inch so divide the offset by 25.4. Lastly - add the converted offset to the wheels center line if the offset is positive for the correct backspacing. Subtract the converted offset to the wheels center line if the offset is negative for the correct backspacing.

    For Example:

    17x9 +12mm offset

    *9" rim width + 1" = 10"
    *10"/2 = 5" (wheels center line)
    *+12mm offset/25.4 = 0.47" (0.50" rounded up)
    *0.50" + 5" = 5.50" Backspace


    17x9 -12mm offset

    *9" rim width + 1" = 10"
    *10"/2 = 5" (wheels center line)
    *-12mm offset/25.4 = 0.47" (0.50" rounded up)
    *0.50" - 5" = 4.50" Backspace


    ***Please note that the wheels center line is the backspacing for 0 offset wheels.

    Last, here is a simple chart to help convert offset and backspace.


    I hope this helps.


    -Matt
    Last edited by Discount Tire; 02-27-2013 at 11:07 PM.
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  2. #2
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    Backspace and Offset, How do they relate?

    Wow, Nobody chimed in on this? We appreciate it Discount. This should be a sticky. Its a very common question with a quick solid answer.


    Paratroopers stay up longer!

  3. #3
    Old Timer JKAnimal's Avatar
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    This is the best explanation and illustration I have seen so far. Thanks for posting this up!

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    Re: Backspace and Offset, How do they relate?

    Hmm what's going on here ? Thanks for the write up. Welcome to Wayalife. You and Mel haven't gone threw proper procedure of giving a wave though. It's good to have some more pros on here.:thumbup:

    Sent from my PC36100 using WAYALIFE mobile app

  5. #5
    Advertiser Discount Tire's Avatar
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    Quote Originally Posted by Tackerdown View Post
    Hmm what's going on here ? Thanks for the write up. Welcome to Wayalife. You and Mel haven't gone threw proper procedure of giving a wave though. It's good to have some more pros on here.:thumbup:

    Sent from my PC36100 using WAYALIFE mobile app
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    Caught the Bug ALRydr's Avatar
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    Backspace and Offset, How do they relate?

    Great post Matt!!! Thanks for taking time to do it!!

  7. #7
    Caught the Bug JK&Beyond's Avatar
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    Quote Originally Posted by Philip *AZ* View Post
    Wow, Nobody chimed in on this? We appreciate it Discount. This should be a sticky. Its a very common question with a quick solid answer.


    Paratroopers stay up longer!
    Agreed. Sticky!

  8. #8
    Advertiser Discount Tire's Avatar
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    Thanks for the kind words. Glad you found this helpful.
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    Hooked BlackRockBurner's Avatar
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    Backspace and Offset, How do they relate?

    X3 on sticky. I'm sure thousands in the future will ask this question.
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    Fresh Catch SP77's Avatar
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    Backspace and Offset, How do they relate?

    Thanks a lot.

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