B'Zerk Lunatic Roller Derby Wheels! Bzerks are for those who love the feel of a wide profile wheel with the benefits of a fully hollow core and cap. This makes Bzerk Wheels super lightweight, fast and with just the right amount of flex. The Bzerk Hollow Cap gradually extends to the edge (lip) of the wheel. This allows for a solid feel similiar to that of aluminum but without the weight, wheel separation or chunking.