actually, you do not need those crappy user-defined stuffs. ZM adds them themselves, i made the E92 without using any.
for the wheels, you need to use the " tire " shader (without the ")
for stuffs with bump (those of what you want to be dirty), use the "mesh" shader
those, you dont want to be dirty, use "generic"
for glass, use "vehglass"
etc... Kotton once inspected them all, its posted somewhere @ KCS.