Car dial design is extreme (7)
I believe the answer is:
radical
'extreme' is the definition.
(I've seen this in another clue)
'car dial design' is the wordplay.
'design' indicates anagramming the letters.
'car'+'dial'='cardial'
'cardial' is an anagram of 'RADICAL'.
'is' is the link.
(Other definitions for radical that I've seen before include "Tending towards extreme political views" , "objections to current policy?" , "Fundamental - non-conformist" , "Primitive" , "Politically extreme" .)