Letters posted when cycling separately causing complaints (8)
I believe the answer is:
ailments
'complaints' is the definition.
('ailment' can be a synonym of 'complaint')
'letters posted when cycling separately' is the wordplay.
I cannot quite see how this works, but
'letters' could be 'ts' (more than one T) and 'ts' is found within the answer.
This may be the basis of the clue (or it may be nonsense).
'causing' acts as a link.
Can you help me to learn more?
(Other definitions for ailments that I've seen before include "Illnesses, complaints" , "Minor illnesses" , "Nail stem produces illnesses" , "Maladies of manliest sort" , "Diseases or disorders" .)