Off road unicycle has two different textures. Clean tire, and dirty tire. The texture is selectable in the Materials panel.
There are two main parenting points. The frame, and the tire. The tire and seat are parented to the frame. All wheel parts, spokes, pedals, crank arms ext, are parented to the tire. Rotate the tire, and all of those parts rotate correctly. Grab the frame and move the model as a whole.