Don't know about you, but I learn best when I can see something - not just read numbers. Just found this calculator which takes wheel, spacer, and tire size, along with wheel offset, into consideration and then shows the position of the original tire compared to the new set-up.

Shows height and width of the old and new tire positions, both vertically and horizontally. Shows the change in proximity of the top of the tire to the fender well and the change in distance from suspension. Even shows the projected change in speedometer reading from old set-up to new.

For this bonehead, the visual is really helpful. To some of you this may be old hat, but for the rest I hope this helps you as much as it does me...

Wheel Offset Calculator