Argument after a number of cars get bigger again (6)
I believe the answer is:
regrow
'cars get bigger again' is the definition.
I can't judge whether this definition defines the answer.
'argument after a number' is the wordplay.
'argument' becomes 'row' (to row is to argue).
'after' says to put letters next to each other.
'a number' becomes 'reg' (registration number on a vehicle).
'row' put after 'reg' is 'REGROW'.
'of' is the link.
Can you help me to learn more?
(Other definitions for regrow that I've seen before include "In a new way" , "develop afresh" .)