Medium SkyLite Wheels with Aluminum Hubs. The secret behind the SkyLite’s unbeatable toughness and lightweight is a foam core surrounded by a durable rubber skin. Unlike hollow tires, our unique foam moulding process provides each wheel with strength and bounce absorption for smoother landings. The outer rubber skin also gives SkyLites excellent wear and durability. In addition to eliminating dead weight, SkyLites have better balance and cannot lose pressure or go flat. These wheels also have heavy duty self centering aluminum hubs with Delrin center bearings. The aluminum hubs can be disassembled if desired. The S850 is the hub only, which can replace the plastic hub in the S879 to S883 series.