Scaled down car's a true representation (9)
I believe the answer is:
miniature
'scaled down' is the definition.
'car's a true representation' is the wordplay.
'car' becomes 'mini' (Mini Cooper**).
'representation' indicates an anagram.
'a'+'true'='atrue'
'atrue' with letters rearranged gives 'ature'.
'mini'+'ature'='MINIATURE'
(Other definitions for miniature that I've seen before include "Diminutive" , "Tiny copy or very small version" , "Little" , "Smaller than normal" , "I ruminate (anag)" .)