I searched but couldn't find the answer. I just picked a set of 4 original 16" rims for a 91 Z28. They have different offset/back spacing. Which go on the front? The ones that set the tire in towards the car more or the ones that set the tire out away from the car more?

 

I believe the rims are marked which ones are front and back, just around the center opening.

 

Yes they are. I looked every where but there. Thank you. Next dumb question. What happens if you put the rears on the fronts? Do they rub somewhere? Or handle poorly?

 

As far as that, I have no idea. I believe they will be too far in to fit around everything.

 

They should be marked. -in the casting (I've owned both style IROC wheels, and they're both marked. I just assumed the z28 wheels are marked too, but maybe not)
Fronts have a zero offset, rear are +16mm.
The 0mm FRONT wheels push the whole wheel OUT more. The 16mm offset would mount IN more, and not stick out as much.

The front can go on the back with no issue. Many guys will get an extra set of fronts and do this because they stick out more and people like the look. Putting rears on the front will likely rub somewhere. Possibly contacting the tie-rod, or maybe interfering with the caliper. I've always heard you can't run them this way but never actually tried, so I can't tell you exactly where the issue is.

 

Rear wheels on the front will get jammed against the tie rod end.

In 89 when I got my first set of replacement tires, I arrived to pick up the car but they couldn't back it out of the garage, it wouldn't move. Turned out they'd installed the rear wheels up front. Once they figured it out and swapped the wheels all was well, and I drove it away.

I did it myself in 2005, though not accidentally. I got a spare set of fronts and rears, removed the fronts from the car, took them and the spare rear wheels to a shop to have the tires swapped onto the rear wheels, went home and installed the spare rear wheels/tires on the front, so the car could be on the ground while the four front wheels were out getting chrome plated. All good... until at some point I tried to push the car, for some reason, but it wouldn't move. Right away I knew why lol.

 

I just put the rears on the front to see for my self and yes the rims hit the tie rod & the strut. I like the idea of being able to rotate the front to rear and such but in reality the little bit I drive the car the tires will probably get dry rot long before they wear out. Thanks for the info.