The most common and most likely answer to this crossword clue is the 14 letter word PENNY-FARTHING
I've seen this crossword clue in Financial Times
P
E
N
N
Y
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F
A
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H
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More clues leading to the result PENNY-FARTHING
Buddy explains!
The straight part
We know that "Old coppers/bike" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case old coppers/bike = penny-farthing.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 PENNY-FARTHING mean?
PENNY-FARTHING noun- A type of bicycle popular in the 19th century, with the front wheel far larger than the rear one.