| "it's easier to just post a quick one" for you, but multiply that every day and you end up with an archive of a million half-answers burying the handful of threads with in-depth information. Here's how offset works.  Zero offset is a centered wheel.  Positive offset shifts the wheel inward that many mm.  So let's say you have an 8" +0 wheel.  You'd have 4" inside the hub surface, and 4" outside. 8" +25 would mount with 5" inboard and 3" outboard...you'd need an extra inch of clearance inside and have the outside 1" more sunk. Going to a 9" with the same offset would add .5" to the inside and outside.  Then going to +38 would shift the wheels 1/2" inward, so inside would need an extra inch (.5+.5), outside would be unchanged (.5-.5). 
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