I still see lots of questions (and confusion) about wheel and tire sizing.
This may help...http://www.rimsntires.com/specspro.jsp
Plug the original tire and wheel size into the left side. Plug your "new" tire and wheel size into the right side.
It will tell you where any interference is likely to be (no guarantees) and how much speedometer error the new size will cause.
Obviously, this is not Fiero-specific. It's completely generic, but it's better than nothing.
88 Formula IMSA Fastback. 4.9, NVG T550
Praise the Lowered!