Dump where 4x4's taken, changing directions (7)
I believe the answer is:
Here is my best explanation:
'dump' is the definition.
I can't explain the rest of the clue.
(Other definitions for offload that I've seen before include "Get rid of (unwanted item or burden)", "Jettison", "Dump", "deliver goods" and "9 [JETTISON]".)