Sponsor to fork out dollars on new tyres (6)
I believe the answer is:
surety
'sponsor' is the definition.
(I know that surety is a type of sponsor)
'dollars on new tyres' is the wordplay.
'dollars' becomes 'u' (I can't justify this - if you can you should believe this answer much more).
'on' is an insertion indicator.
'new' indicates anagramming the letters.
'tyres' anagrammed gives 'srety'.
'u' going inside 'srety' is 'SURETY'.
'to fork out' is the link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for surety that I've seen before include "Guarantor" , "Semitic language" , "Warranty, guarantee" , "Safeguard; certainty" , "One who takes responsibility for another's debts" .)