Observe what's wrong about maximum speed (5)
I believe the answer is:
watch
'observe' is the definition.
(I've seen this before)
'what's wrong about maximum speed' is the wordplay.
'wrong' indicates an anagram.
'about' indicates putting letters inside.
'maximum speed' becomes 'c' (I've seen this in other clues).
'what' is an anagram of 'wath'.
'wath' going around 'c' is 'WATCH'.
(Other definitions for watch that I've seen before include "See 21" , "Keep an eye on - timepiece" , "Timepiece - look out" , "Look at attentively" , "Observe - timepiece" .)