Let's go travelling, tour's beginning on your bike (3,4)
I believe the answer is:
get lost
'on your bike' is the definition.
(both are rude ways of telling someone to go away)
'let's go travelling tour's beginning' is the wordplay.
'travelling' indicates an anagram.
'beginning' says to take the initial letters.
The first letter of 'tours' is 't'.
'lets'+'go'='letsgo'
'letsgo' is an anagram of 'getlos'.
'getlos'+'t'='GET LOST!'
(Other definitions for get lost that I've seen before include "without the map?" , "Stray" , "beat it" , "Stop pestering me!" , "Might bad map readers" .)