A drivable wheel, like a single huge wheel you can fit someone into. Think of this race from one of Broughy1322's videos (wheel showcase starts at 0:45, wheel race at 10:37).
you wont believe i just found out there is drivable air ingame. thats right no mods. you press shift+c and you can move air with the keys! edit: omg it works with water too!
Drivable small Trailer. Probably move the a axles to rear and add ex. Bluebuck front axle, to the front. --- Post updated --- And Electric powertrain