Two distinct uses. (1) Short for
三轮车 (sānlúnchē, three-wheeled cycle/cart) — pedicabs, cargo trikes, electric trikes are everywhere in Chinese cities. (2) Counting rounds:
三轮 here is
三 'three' +
轮 'round/turn', e.g.
三轮谈判 (three rounds of negotiations),
三轮融资 (Series C financing — though confusingly Chinese tech press also uses 'C
轮').
