How many transformations does Drive Knight have? In the last chapter of the manga, Drive Knight transformed into


   a sort of motorcycle. 


In a past chapter of the manga and episode of the anime IIRC, he transformed into a centaur. Does he have more transformations?  How many transformations does Drive Knight have?
Yes, he has more transformations. From the wiki, Drive Knight has 6 Tactical Transformations. These are:


Knight (桂馬, Keima): Drive Knight shapes his lower body into that of a horse, giving him the appearance of a centaur.
Silver (銀, Gin): Drive Knight forms a long sword.
Chariot (香車, Kyōsha): Drive Knight transforms into a sleek motorbike.
Flying Chariot (飛車, Hisha): Drive Knight transforms into a bulky compact projectile with four wings and forms rocket engines that propel him forward.
Bishop (角, Kaku): Drive Knight transforms into a large humanoid robot with a crested helmet.
Gold (金, Kin): Drive Knight adds a layer of armor to his body. His hair turns white and his armor flares between its plates.


All in all, he has a total of six transformations. The ones you saw were the Knight and Chariot transformations. As @AkiTanaka mentioned, these are named after shogi pieces.