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.