Saying something seconds before reaching the top (8)
I believe the answer is:
speaking
'saying something' is the definition.
(I've seen this before)
'seconds before reaching the top' is the wordplay.
'seconds' becomes 's' (abbreviation).
'before' is a charade indicator (letters next to each other).
'reaching the top' becomes 'peaking' (reaching the peak).
's'+'peaking'='SPEAKING'
(Other definitions for speaking that I've seen before include "oratory" , "Conversing" , "conveying meaning" , "a way of passing the word" , "Talking" .)