I'm new to the LS1 Tech Forum. I have just recently purchased a '98 Z28 and have been researching wheels tires and suspension mods to set the car up for Track Days (Road Course). I previously owned both a 5th Gen and 6th Gen Camaro and the choices for wheels were a little easier in determining what fit and what didn't. Someone may have done this already but I didn't see it anywhere.

To help determine what offsets worked with the varying width wheels, I made this spread sheet that will calculate out the front and rear spacing from the actual wheel mounting surface on the car. So instead of wondering what fits, how much room do I have from the inner fender liner, will it be tucked in, will it be flush or will it stick out, now all you have to do is measure inward and outwards from the wheel mounting surface and compare to the chart. I've already punched in round numbers from 25 to 60 but you can download the Excel file and just type in the desired offset and it will calculate spacing for both backspacing and front spacing. No more wondering if it will fit. Note this does NOT include the tire, just the wheel. I used widths from 9 up to 12. I haven't seen a lot of questions concerning wheels less than 9" and bigger than a 12 will require major modifications (more than the 12 already requires).

Just for clarification and make sure we are all on the same page, here are the definitions for the labeling in the spread sheet. Some may use slightly different terminology.....
1) Offset is in millimeters. I only did positive offsets so if you need negative, you will have to type a minus in front of the number you type in. It still works. I converted the offset to inches in the 2nd column just for informational purposes.
2) Center Line - this is the center of the wheel from the outside edges. As you know, a 9" wide wheel measure 10" from outside edge to outside edge, so the center line value takes this into account. Offset is measured from the Center line.
3) Front Spacing - distance away from the mounting surface (rotor hat of the brake rotor) towards the outside of the car
4) Back Spacing - distance from same mounting surface towards the middle of the car and inner fender well

If you download the file, only type in the offset MM column. All calculations are pointed to that value. If you type somewhere else, it won't give correct answers.

Here is a screen shot


Hope this helps some of you....

Len