Offset change with new lips

[jking]

I have always thought that when adding 1" to the lip you subtract 25.4mm from the offset because it is moving the center of the wheel away from the mounting pad out 25.4mm. Why would it only be half (12.7mm according to the sticky). I have read the sticky over a couple times and it's still only confusing me more. I'm also very tired rite now not helping. Someone explain how 12.7mm is correct or 25.4mm is correct.

[Oh, Word?]

-12mm per inch you add is correct.

[ThomasChagrin]

You split the added width on each side of the wheel, as far as the offset goes. Well, this is a bit more confusing because you're adding the inch to the outside. For reference and as a baseline to maybe help with the confusion, if you compare an 8.5" +35 to a 9.5" +35, the 9.5" wheel will only sit out farther by a half inch (12mm or so). Half inch on the front and half inch on the back if the offset is the same. God, I think that I'm just being more confusing. Sorry!

[KyleAnderson]

If you add an inch to one side of the wheel, the center line of the wheel is now a half inch closer to that side.

Go to willtheyfit.com and plug these sizes in:

205/40/17x8.5 et40

205/40/17x9.5 et28

Take a look at the comparison picture. You'll see the extra inch is on the outside of the wheel, but because the center of the wheel moved a half inch closer to that side, your offset only drops 12mm.