I made a quick drawing in paint (Am I the next Picasso or what?). The left side of the picture is the inside of the car, and the right side(blue side) faces the street.



The red line is the centerline of the wheel. The left "wheel" shows a negative offset, and the right "wheel" show a positive offset. The left wheel is what a blank might look like and would have a negative(low) offset from the start, but would be machined down to have a positive(high) offset. Machining the mounting pad down on a single piece wheel has the same effect as moving the face of a multi piece wheel out(minimizing the lip).

Same concept as the picture you posted, where the picture shows that the right side of the wheel faces the street. The thing in the middle of the wheel isnt the mounting pad but the center cap (or knockoff hub).

Edit: Another quick thought. Multi piece wheels that have a low offset will stick out, but a single piece wheel with a low offset will tuck more. Thats the big thing to remember. Thats one thing most people dont know about the wheel offset concept.

 

I think you have an artistic future.

 

I am afraid confusion still reigns supreme.
If you take a typical +51mm offset Porsche front wheel and remove 5mm of material from the backpad, the positive offset is increased to +56mm.
(this assumes there is enough material to cut away).
Conversely, if you install a 5mm spacer to that same +51mm wheel, the offset moves in a negative direction to +46mm.
In measuring offset, one must consider the entire width of the wheel, not just the distance between the bead seats. For example, a wheel that has a published width of 8.5 inches is actually about 9 inches wide in total. Therefore the "zero" offset point is actually 4.5 inches.

 

Im glad someone has faith in my talent. Did the picture help Greg?

It does seem counter intuitive that pushing the wheel out means it has lower offset, but we can blame it on whoever came up with that system.

Forgedwheeler is also correct, offset isnt measured in relation to bead seat(but wheel width is) but to the outside lip of the wheel. Bead seat is actually about an inch narrower than the outside lip, not usually a half inch. If you want I can grab a wheel Monday and take a pic so you can see what I mean.