Example 1:
From vclassics (http://vclassics.com/archive/wheeltip.htm):

"6"-wide wheel should protrude 3-1/2" inboard and 2-1/2" outboard, which is a positive offset of 1""

Example 2:
From this and other sites: http://www.eastwoodco.com/jump.jsp?itemID=1441&itemType=CATEGORY&iMainCat=688&iSubCat=1441

"Offset on the other hand is the dimension that represents the difference between the exact centerline of the wheel and that of the inner wheel face that bolts to the flange.

Wheel Width at Outer Rim: 8.5”
Calculate Centerline: 8.5 / 2 = 4.25”
Measure Backspace: 3.75”
Calculate Offset: 4.25 - 3.75 = .50”"


So, if I use how the bottom calculation for a 6" rim with 3.5" backspacing I get:

Wheel Width at Outer Rim: 6”
Calculate Centerline: 6 / 2 = 3.0”
Measure Backspace: 3.5”
Calculate Offset: 3.0 - 3.5 = .50"

That's a .50"(13mm) positive offset, not a 1" (25mm) positive offset as stated on the vclassic site.

To get 1" positive offset on a 6" rim, wouldn't it need a 4" backspacing?:

Wheel Width at Outer Rim: 6”
Calculate Centerline: 6 / 2 = 3.0”
Measure Backspace: 4.0”
Calculate Offset: 3.0 - 4.0 = 1.0"

Can somebody clarify? I've always taken the vclassic statement that Volvos had a positive 1" offset and that a 6" wheel would have a 3.5" backspacing.

Paul

Actually, this site has a pretty good graphic on how to calculate offset too(very bottom of page):

http://www.tirereview.com/?type=cc&id=179&53L3c73d=179#ratio