Car transmission choice (4)
I believe the answer is:
gear
'car transmission choice' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for gear that I've seen before include "Equipment, clothing, goods" , "Toothed wheel which engages with another one" , "Illicit drugs (slang) - kit" , "Equipment; car mechanism" , "often changed in a saloon" .)