When cycling, trust old instrument (4)

I believe the answer is:

lyre

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'old instrument' is the definition.
(I've seen this before)

I can't explain the remainder of the clue.

(Other definitions for lyre that I've seen before include "Ancient musical instrument - sounds mendacious" , "Early harp" , "Type of harp" , "Ancient Greek stringed instrument" , "Old musical instrument with strings in U-shaped frame" .)

I've seen this clue in The Telegraph.

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