Painful rides might result in subconscious mistake (8,4)
I believe the answer is:
freudian slip
'subconscious mistake' is the definition.
'painful rides might result in' is the wordplay.
'might result in' indicates an anagram.
'painful'+'rides'='painfulrides'
'painfulrides' anagrammed gives 'FREUDIAN SLIP'.
(Other definitions for freudian slip that I've seen before include "Spoken error revealing unconscious thought" , "Words revealing unconscious thoughts" , "Unintentional error" , "It betrays unconscious desires" , "Error betraying inner thoughts" .)