Someone else can better explain offset... Its basically a measurement of the space difference between where the wheel bolts to the hub to the plane going though the center of the tire. Spacers definitely change that. You would consider the spacer to be part of the wheel when measuring the offset.

What I'll say here though is that I'd think a 185 section width is an awful narrow tire for a 7" rim. I think you'd want at least 205. Thats what I've got on my 1800. And, 215/70 at the rear is gonna be real tall... and fairly wide. You might run into clearance troubles... probably the inside edges of the outer fenders since you've got spacers back there.

I'd lean towards 205/65 both front and rear.

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-Matt I ♥ my ♂