Change of speed leads to speed which is reckless (9)
I believe the answer is:
desperate
'is reckless' is the definition.
(thesaurus)
'change of speed leads to speed' is the wordplay.
'change of' indicates an anagram.
'leads' is a charade indicator (letters next to each other).
'to speed' becomes 'rate' (rate is a kind of speed**).
'speed' with letters rearranged gives 'despe'.
'despe'+'rate'='DESPERATE'
'which' acts as a link.
(Other definitions for desperate that I've seen before include "Eater sped to beyond hope" , "Hopeless; extremely bad" , "Adept seer (anag)" , "Miserable" , "critical" .)