Short race on your bike (4)
I believe the answer is:
shoo
'on your bike' is the definition.
(both can be used to tell someone to go away)
'short race' is the wordplay.
'short' means to remove the last letter.
'race' becomes 'shoot' (shoot can mean to run or race off).
'shoot' with its final letter taken off is 'SHOO'.
(Other definitions for shoo that I've seen before include "Dismiss" , "Word used to frighten away animals" , "Shove off!" , "told to go away!" , "word of dismissal" .)