around 16-18 % chromium , 8 % nickel ( for stability and to make the disc non-magnetic and less brittle at low temperatures ), and a little carbon ( no more than 2 %), for hardness and strength . Ductile Iron : Ductile iron is an iron-carbonsilicon alloy , and these discs are more commonly used for racing bikes . More flexible than other cast iron varieties , ductile iron provides better braking performance than stainless steel as it conducts heat better ( stainless steel doesn ’ t dissipate heat as well as ductile iron , as its chromium outer layer stores heat up instead of getting rid of it ). Since brakes basically convert movement into heat [ via the friction of pads against discs ], effective heat dissipation is paramount , especially in racing applications . Ductile iron also produces a much higher coefficient of friction ( braking power ).

What are some of the issues ? In some stainless steel discs , small cracks can occur near the drill / vent holes on the disc , normally caused by thermal cyclic strain ( the heating / cooling cycles occurring during braking ), and mechanical input through braking torque , so it ’ s crucial a high enough quality stainless steel is used in initial manufacture .

KIWI RIDER 69