The most common and most likely answer to this crossword clue is the 9 letter word TAILPIPES
I've seen this crossword clue in The Daily Telegraph
T
A
I
L
P
I
P
E
S
Buddy explains!
The straight part
We know that "which protrude from rear of car" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case which protrude from rear of car = tailpipes.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does TAILPIPES mean?
TAILPIPES noun- An exhaust pipe (on a vehicle) (in any configuration)
- An exhaust pipe exhausting to the aft of the vehicle