Ever since the fingerboard exploded onto the youth culture scene, big companies like Tech Deck have been releasing pretty realistic looking miniature skateboards. Complete with beautiful graphics and die-cast metal trucks. Mini tires are nearly identical to their full-size cousins with the notable exception of the wheel bearings.
Bearings are the small metal rings inside a skateboard wheel that allow it to roll smoothly. A standard fingerboard is not made with wheel bearings included. Without the bearing, the wheel simply sits directly on the truck, causing friction and slowing the wheel down. Bearings, on the other hand, are made of metal and when placed in the fretboard truck they create a smooth motion.
Another advantage tread wheels have over flat wheels is that on almost any surface, tread wheels roll freely with little resistance. Often, if a surface is smooth, standard wheels will stop rolling altogether. This is not a problem with bearing wheels, as no matter what surface the fretboard is on, the trucks stay in contact with the bearings.
The wheel with the included bearing also creates a more realistic look. For enthusiasts trying to create the most authentic look possible with their finger skateboard bearings these are a must have. The wheel itself can be standard molded plastic or a variety of other materials with various colors.
The only really obvious advantage to standard bearingless wheels is cost. Custom wheels with bearings can be quite expensive and can take months. While normal wheels can be found, get out easily.