Travel free, heading east (4)
I believe the answer is:
Here is my best explanation:
'travel' is the definition.
(ride is a kind of travel)
'free heading east' is the subsidiary indication.
'free' becomes 'rid' ('rid' can be a synonym of 'free'**).
'heading east' becomes 'e' (abbreviation).
(Other definitions for ride that I've seen before include "Take journey", "Travel (on a bike, perhaps)", "Travel, by horse say", "Fairground attraction; go on horseback", "Travel on (a bicycle)", "Go on horseback", "Go by horse", "Travel in or be carried on", "Travel on the back of animal" and "Journey as passenger".)