Once on the outside, we start to work in tandem? (3-6)
I believe the answer is:
two-seater
'tandem?' is the definition.
(a tandem is a two-seater bike)
'once on the outside we start to work' is the wordplay.
'on the outside' says to hollow out the word (remove centre letters).
'to work' is an anagram indicator.
'once' with its centre removed is 'oe'.
'oe'+'we'+'start'='oewestart'
'oewestart' is an anagram of 'TWO-SEATER'.
'in' acts as a link.
(Other definitions for two-seater that I've seen before include "Sports car" , "Small car" .)