Hubs provide the connection between the wheels and the bike's frame. They ensure a smooth, fast ride with as little play as possible. When purchasing a racing bike hub, compatibility with the other components on the bike is crucial. The axle system should be taken into account (quick release or thru-axle), as well as the freewheel body on the rear wheel (Shimano/SRAM or Campagnolo), the type of brakes (disc or rim) and of course the dimensions. The fewer holes or spokes the hub has, the more aerodynamic the wheel becomes, which can save you valuable seconds in competition.