Drove over the limit (7)
(Another definition for speeded that I've seen is " Went very fast".)
'drove over the limit' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for sped that I've seen before include "Raced, hurried" , "was 8 [FLEET]" , "Dashed" , "Went quickly" , "Went fast" .)