Unsightly padding the motorist may fall back on? (5,4)
I believe the answer is:
spare tyre
This clue is a double definition.
'unsightly padding' is the first definition.
(spare tyre can mean belly fat)
'the motorist may fall back on?' is the second definition.
(a motorist might use a spare tyre)
(Other definitions for spare tyre that I've seen before include "could replace flat" , "sign of over-indulgence?" , "Something needed for flat" , "Something kept for the flat" , "Roll of fat around the waist, like car part" .)