The most common and most likely answer to this crossword clue is the 8 letter word CHARIOTS
I've seen this crossword clue in The Daily Telegraph
C
H
A
R
I
O
T
S
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The straight part
We know that "Old racing cars" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case old racing cars = chariots.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 CHARIOTS mean?
CHARIOTS noun- A two-wheeled horse-drawn vehicle, used in Bronze Age and Early Iron Age warfare.
- A light four-wheeled carriage used for ceremonial or pleasure purposes.
- (xiangqi) rook