Brake drums ; cast iron vs ductil cast iron .

[Duffy1]

Just received Bratton`s 2013 catalogue . In the brake section they offer U.S. made ductile cast iron brake drums which they say are 2 times as strong (?) as cast iron brake drums . Just my luck . I just completed a brake job on my 31 s/w installing U.S. made cast iron brake drums from Snyders . So the question is . How much ( 2x ?) better does ductile cast iron drums stop than cast iron drums. All feed back appreciated .