Combine drum kits with roller frame to create unique professional level trainer. Challenger: spun alloy drums with polycarbonate end caps. Alloy: spun alloy drums with alloy end caps . Includes 3 rollers, roller belt, and mounting hardware. Rolling resistance increases as the roller diameters decrease. Features: Smaller diameter drums provide more resistance Alloy drums and Challenger 4.5" drums are recommended for use with the Killer Headwind Fan Alloy drums are longer lasting and provide a smoother, more road-like ride Alloy drums use CNC machined alloy end caps Kreitler rollers utilize modular technology and have a lifetime warranty Purchase each component individually to make a set of rollers Alloy end caps are the longest lasting, compatible with all accessories and give the truest feel of being on the road Smaller drums = more resistance All drum kits include roller belt Killer Headwind compatible