Quote:
Originally Posted by Twoxentrix
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Unless I'm mistaken you seem to have the offset in reverse. According to the picture in your link a -12mm offset will inset (rather than push out) the centerline of the wheel about 1/2".
Apparently, a 265/70-17,275/70-17and 285/70-17 will comfortably fit a 8"x17' wheel for those looking for a mainly 2WD setup. The same -12mm offset keeps the wheel centered.
I bought 17" wheels mounted with tires from the Tire Rack back in about 1999 for my 1997 E-350 RB. I never understood where the offset came from that they selected but after reading this thread it seems obvious that if you go from a zero offset 7" wide stock wheel to an 8" wide wheel the offset should be set to -12mm to keep the centerline of the wheel tire in the same place.
Basically, the extra inch in width would correspond to a 1/2" shift outboard in the wheel centerline. Adding -12mm (approx 1/2") offset compensates and brings the wheel centerline back the same as stock (close enough 25.4/2=12.7mm).