Consent to change gear at the end of the race (5)
I believe the answer is:
agree
'consent to' is the definition.
(agreeing is a kind of consenting to)
'change gear at the end of the race' is the wordplay.
'change' indicates an anagram.
'at' means one lot of letters go next to another.
'the end of the' suggests the final letters.
The last letter of 'race' is 'e'.
'gear' anagrammed gives 'agre'.
'agre'+'e'='AGREE'
(Other definitions for agree that I've seen before include "Accord, match" , "Settle" , "Match; tally" , "Think alike" , "Concur, acquiesce" .)