gm wheels

does anyone know if most of the gm wheels will fit onto a 91 lumina? i know gm has a couple different lug patterns, but most of them are 5 x 115. i know the lumina is 5 x 115. i also know that wheels have different offsets. so i'm wondering if theres a difference in offset in most wheels from the lumina and if it couldnt be corrected with spacers.

on a side note, if i were to upgrade to larger rims, then obviously the height of the tire would have to change, so what is like 2 inches in rim size worth in that tire code on the side of the tire?

For example: P245/55ZR18:
the 245 is the distance, (in mm) from bead to bead. the 55 is the ratio of tread vs. sidewall of the overall distance from bead to bead. Z = speed rating, R = radial, 18 is rim diameter (in inches). It's too early in the morning for me to calculate a match in a 17 or 18 inch wheel, but with this info you may be able to.

your partially correct and partially wrong (dwalmop) here is a website that tells exactly what the tire size means...
http://www.discounttiredirect.com/direct/brochure/info/tmpInfoReadingSidewall.jsp

good informational site. However, I'm not seeing where I'm wrong (except nomenclature). bead - bead = sidewall - sidewall.