Gets too big, perhaps, to go on tours in the west (8)

'tours in the west' is the definition.
Although both the answer and definition are verbs in their -s form, I can't understand how one could define the other.

'gets too big perhaps to go' is the wordplay.
I cannot really see how this works, but
'gets' could be 'grows' ('grow' can be a synonym of 'get') and 'grows' is present in the answer.
The remaining letters 'out' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).

'on' is the link.

Can you help me to learn more?