Repaired tyres became serrated (8)
I believe the answer is:
retreads
'repaired tyres' is the definition.
'retreads' can be an answer for 'tyres' (retread is a kind of tyre). I'm not sure about the 'repaired' bit.
'became serrated' is the wordplay.
'became' is an anagram indicator (I've seen 'become' mean this).
'serrated' is an anagram of 'RETREADS'.
Can you help me to learn more?
(Other definitions for retreads that I've seen before include "Arrested over resurfaced tyres" , "Serrated like tyres restored for use" , "Serrated like remoulded tyres" , "recovered tyres" , "They gain fresh employment" .)