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Yokomo Aluminium Rear H-Arm (Weight Spec / Short).
These are optional parts for the RD2.0/SD2.0 that allow you to systematically increase rear traction by combining aluminum rear H-arms with brass weights. By using highly rigid aluminum H-arms and mounting these separately sold weights, you can increase the unsprung weight that places a direct load on the rear tires, effectively boosting tire traction.