A rotor hub for an aircraft that includes a yoke, a rotor mast; and a hub spring assembly. The hub spring assembly includes an upper outer member; an upper inner member; and an upper spring member having a plurality of elastomeric layers and shim layers sandwiched between the upper outer member and the upper inner member, the shim layers being tapered such that a thickness of each shim layer is smaller at a side portion as compared to the thickness of the shim at a center portion.