Hello,

this is a quad or quad bike or ATV (All-Terrain Vehicle) but I didn't want to call it all-terrain vehicle because there are many more all-terrain vehicles than just quads. Anyway, if you're asking why it's so big that's because of the wheel size. For a realistic size the wheels would have to be only half or even less than half a block high. This would make it impossible to build a recognizable quad.
The idea for this build came from RevenJoakimMc and Momu.

Enjoy!