Put weight behind reflective backing track (11)
I believe the answer is:
silverstone
'reflective backing track' is the definition.
'silverstone' can be an answer for 'track' (I've seen this before). I am unsure of the 'reflective backing' bit.
'put weight behind' is the wordplay.
'put' becomes 'silver' (I can't justify this - if you can you should give a lot more credence to this answer).
'weight' becomes 'stone' (stone is a unit of weight).
'behind' is a charade indicator (letters next to each other).
'silver'+'stone'='SILVERSTONE'
Can you help me to learn more?
(Other definitions for silverstone that I've seen before include "English race track" , "place for motorists - with 24d" , "Northamptonshire motor-racing circuit" , "English motor racing circuit" , "UK motor racing circuit" .)