Aluminium rim & carbon structure in either 50mm or 80mm profiles. Aluminium hub body with oversized flange on drive-side. Bearings: A choice of either standard bearings or Fulcrums USB (Universal Serial Bus) bearings using the best ceramic bearings available on the market – Silicon Nitride. USB (Universal Serial Bus) bearings over standard bearings are 30% lighter 40% more resistant & 50% smoother. Fulcrum Dynamic Balance in the rim: thanks to special operation of the production process the carbon fibre layup is positioned in such a way as to obtain perfect rim balance. The 50 mm's have 18 front radial stainless-steel spokes & 21 at the rear; the 80mm version has 16 front & 18 rear both in Fulcrum 2:1 ratio for greater wheel stability & enhanced power transfer to the rear wheel. They feature the anti-rotation system keeping them aero at all times.