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Technical Wheel offset & back space?

Discussion in 'The Hokey Ass Message Board' started by TudorTony, Jun 5, 2019.

  1. TudorTony
    Joined: Jun 2, 2013
    Posts: 198

    TudorTony
    Member
    from NJ

    My dyslexia screws me up with these two terms. Question, if I have 0 offset w 4” back space now & want to move the wheel further under the wheel well by 2” would I go to a -2” offset & 6” backspace?
     
  2. alchemy
    Joined: Sep 27, 2002
    Posts: 13,845

    alchemy
    Member

    That's the way I understand it.
     
  3. DDDenny
    Joined: Feb 6, 2015
    Posts: 11,637

    DDDenny
    Member
    from oregon

    My best advise has always been to just not use the term "offset", especially when ordering any kind of custom wheel, you might "think" you understand it but if not it could be an expensive misunderstanding.
    Pretty hard to mess up by using "frontspace" and "backspace", pretty standard terminology nowadays.
    The other mistake people make in calling out wheel width is using the overal outer edge dimensions in measuring wheels, it's the dimension between the bead seat flanges that dictate wheel size.
     
    alchemy likes this.
  4. squirrel
    Joined: Sep 23, 2004
    Posts: 42,690

    squirrel
    Member

    Actually wheel width is measured using the inner dimension of the bead flanges, but backspace is measured from the outside of the flange.

    Offset, it doesn't matter which you use, as long as you use the same surface on both sides of the wheel
     
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  5. Offset is based off of the center plane of the wheel, which is located halfway between the two bead surfaces. This is assuredly the most accurate method as it isn't dependent upon the height of the lip on the backside of the rim, which can vary from rim to rim for a given width. OEMs and wheel manufacturers specify (or can specify) their wheels using offset.

    A negative offset will have the hub surface located in the inboard half of the wheel (towards the car's centerline).
    A positive offset will have the hub surface located in the outboard half of the wheel.

    So, in your case, you're increase in backspacing by 2" also increase the offset by 2".
     
    Last edited: Jun 5, 2019
  6. DDDenny
    Joined: Feb 6, 2015
    Posts: 11,637

    DDDenny
    Member
    from oregon

    On a full fendered car where space is at a minimum the tires' sidewall bulge needs to be a consideration too.
     

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