Because the process of forging the wheel is the use of high pressure (most of the pressure of several thousand tons) will have a heated alloy pressed into the hub of the rough embryo (prototype), and then fine CNC engraving secondary processing, due to withstand high pressure.

  So that the molecules between the alloy will be smaller, the gap will be more fine, the density will be higher, the interaction between the material molecules will be stronger, so the wheels only need less raw materials will be able to achieve sufficient rigidity, so that the whole Lighter weight.