Race on motorway for a group of mates (5)
I believe the answer is:
harem
'a group of mates' is the definition.
(harem can mean a group of animals for breeding)
'race on motorway' is the wordplay.
'race' becomes 'hare' (hare can mean to run fast).
'on' says to put letters next to each other.
'motorway' becomes 'M' (as in motorway names - M1, M4 etc).
'hare'+'m'='HAREM'
'for' acts as a link.
(Other definitions for harem that I've seen before include "Concubines living together" , "Place for women" , "Quarters for women in Muslim household, a seraglio" , "Living quarters of wives in a Muslim household" , "A lot of females" .)