Tyre part found underground (4)
I believe the answer is:
tube
This clue might be a double definition.
'tyre part' is the first definition.
'tube' can be an answer for 'part' (tube is a kind of part). I'm unsure of the 'tyre' bit.
'underground' is the second definition.
(the London Underground is nicknamed the Tube)
'found' acts as a link.
Can you help me to learn more?
(Other definitions for tube that I've seen before include "train network" , "Pipe - railway" , "Hollow cylindrical object" , "appearing tinny?" , "Long, hollow cylinder" .)