Tyre so bald, sons twice pulled out foot-lever (7)

I believe the answer is:

treadle

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'foot-lever' is the definition.
(I've seen this before)

I can't explain the rest of the clue.

(Other definitions for treadle that I've seen before include "Foot-pedal" , "driving mechanism" , "machine operator" , "(Machine's) foot-control" , "Machine foot-lever" .)

I've seen this clue in The Independent.

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