Carriage's following river in Russia (8)
I believe the answer is:
postural
'carriage's' is the definition.
(I know this)
'following river in russia' is the wordplay.
'following' becomes 'post' (eg post-war, post-industrial etc).
'river in russia' becomes 'ural' (the Ural is a Russian river).
'post'+'ural'='POSTURAL'
(Other definitions for postural that I've seen before include "Relating to carriage" , "Description of carriage" , "Relating to pose" , "Relating to bearing or attitude" .)