Offset, Width Basics
Offset
The offset of a wheel is the distance from its hub mounting surface to the centerline of the wheel. The offsets are measured in millimeters.
Backspace
Similar to offset, is the distance from the hub mounting surface to the inside lip of the wheel (measured in inches).
0 Offset
The hub mounting surface is even with the centerline of the wheel.
Postive (+) Offset
The hub mounting surface is toward the front or wheel side of the wheel.
Negative (-) Offset
The hub mounting surface is toward the back or brake side of the wheels centerline.
The magic formula
1″ = 25.4mm
What does this mean to you?
Higher offset = Outer lip is more in, towards the inside of the fender (tuck). This equals less lip.
Lower offset = Outer lip is more out, towards the outside of the fender (poke). This equals more lip.
When the width of the wheel changes, the offset also changes numerically. If the offset were to stay the same while you changed width, the difference of width would be split evenly between the inside and outside. For example, splitting 1″ of width evenly would be.
1″ of width = 25mm / 2 = 12.5mm to both sides.
The exception to this rule is if one were to replace an inner or outer rim half.
Let’s take the ever so popular BBS RS for example. Say you owned some BBS RS with 1″ lips on em. If you wanted to add more dish, you could add 1″ bigger outers, making it a 2″ lip. By doing this, you effectively made the offset lower by 25mm, and increasing the width by 1″. Let’s say you did that to the front and you wanted 3″ lips in the rear. You would add 2″ bigger outers, making it a 3″ lip. That makes the rear wheel 50mm lower in offset, and 2″ bigger in width. Also remember, we’re doing this in even numbers to keep things simple. If you were doing a 2.5″ lip (instead of 3″), the offset difference would be 1.5 x 25mm = 37.5mm, and the width would increase by 1.5″.
Remember that the above can also work if you need to make bring your wheels in more. Why would you want to that you say? Well what if you’re poking so much there’s just nothing you can do about it? Or let’s say, you want to maximize the lip while not poking as much. If you increase the inner rim half, you are adding width and increasing offset.
I hope that makes sense. Read it again if you need to.
Click the link below for the offset calculator I use. Remember this does not work if you swapping inners or outers.
