Sort of car, say, behind back of bike (6)
I believe the answer is:
estate
'sort of car' is the definition.
(I've seen this before)
'say behind back of bike' is the wordplay.
'say' becomes 'state' ('state' can be a synonym of 'say'**).
'behind' is a charade indicator (letters next to each other).
'back of' indicates one should take the final letters.
The final letter of 'bike' is 'e'.
'state' after 'e' is 'ESTATE'.
(Other definitions for estate that I've seen before include "Property, holdings" , "The entire property of a deceased person" , "Demesne" , "Total possessions" , "Land with buildings" .)