Are good racing drivers, though making a bloomer (9)
I believe the answer is:
speedwell
'bloomer' is the definition.
(I know that speedwell is a type of bloomer)
'are good' is the wordplay.
'are' becomes 'speed' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'good' becomes 'well' (similar in meaning).
'speed'+'well'='SPEEDWELL'
'racing drivers though making a' is the link.
This may not be right. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for speedwell that I've seen before include "Flowering plant" , "Small creeping herbaceous plant with blue or pink flowers" , "Small blue flower of the genus veronica" , "Small plant, veronica" , "bloomer?" .)