A spare tyre? (4)
I believe the answer is:
flab
'a spare tyre?' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for flab that I've seen before include "Excess body fat" , "Informally, unsightly fat" , "Ugly, surplus flesh" , "Excess fat (colloq.)" , "Sign of overeating" .)