Small vehicles strikingly unpopular! (5)
I believe the answer is:
scabs
'strikingly unpopular' is the definition.
I can't judge whether this definition defines the answer.
'small vehicles' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'vehicles' becomes 'cabs' (cab is a kind of vehicle).
's'+'cabs'='SCABS'
Can you help me to learn more?
(Other definitions for scabs that I've seen before include "Wound crusts" , "They continue to work" , "Blacklegs, strikebreakers" .)