How many letters does the top answer for “one who rides a bicycle.” have?

The most common answer is bicycler (8 letters).

Crossword clue: one who rides a bicycle.

1 answer found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).

bicycler 8 letters web-def

a person who rides a bicycle

a person who rides a bicycle 50% similar → bicycler, bicyclist, biker

one who rides on a velocipede. 50% similar → velocipedist