Bicycle 30 knife reverse brake and 40 knife reverse brake difference
30 knife down brakes with 40 knife down brake with cutter wheel using reverse brake drum.
Bicycle terminology, "knife" means the knife ring (a type of rim). "Brake" means reverse brake drum.
The difference is 30 knife down brake rim height of 30 mm, and 40 knife down brake rim height of 40 mm. The 30 knife reverse brake is smaller than the 40 knife, and the weight is lighter. It is suitable for climbing. 40 knife reverse brake than 30 knife brake more thick, heavier, inertia better, suitable for breaking the wind.
