Pontiac 2008 Grand Prix Owner's Manual page 374

CAUTION:
{
Rust or dirt on a wheel or other parts to which
it is fastened, can make the wheel nuts
become loose and eventually the wheel could
come off and cause a crash. Always remove all
rust and dirt from wheels and other parts.
5-104
9. Install the compact spare tire.
8. Remove any rust or dirt
from the wheel bolts,
mounting surfaces
and spare wheel.