Some share a ride back (4)
I believe the answer is:
rear
'back' is the definition.
(something's rear is its back)
'some share a ride' is the wordplay.
'some' indicates the answer is hidden within the clue (some of the parts of the word are used).
'REAR' is hidden in the letters of 'share a ride'.
(Other definitions for rear that I've seen before include "Raise; behind" , "Bottom" , "Rare at the back" , "Hind part" , "early, long before now" .)