Pet, what are you in after nine gear changes? (6)
I believe the answer is:
kitten
'pet' is the definition.
(cats are often kept as pets)
'are you in after nine gear changes?' is the wordplay.
I cannot quite understand how this works, but
'gear' could be 'kit' (kit is a kind of gear) and 'kit' is present in the answer.
The remaining letters 'ten' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
'what' is the link.
(Other definitions for kitten that I've seen before include "Beatrix Potter's Tom, say" , "Baby cat" , "Little Tom, perhaps" , "Immature cat" , "Fluffy little animal" .)