Treacherous types: racers, perhaps (6)
I believe the answer is:
snakes
I believe this is a double definition.
'treacherous types' is the first definition.
(snake can mean a treacherous person)
'racers perhaps' is the second definition.
(racer is a type of snake)
(Other definitions for snakes that I've seen before include "Adders, cobras, rattlers etc" , "Winds; adders" , "[CREES]" , "Go down them on board" , "Eg, cottonmouths, boas" .)