The invention concerns a timepiece balance (1), with inertia adjustment including a hub (2) pivoting about a balance staff (3) and a felloe (5), connected to said hub (2) by a joining surface (6).It is wherein said felloe (5) is made in a single piece with said joining surface (6) and said hub (2) in a micro-machinable material, or silicon, or quartz, or a compound thereof, or an alloy derived from MEMS technology, or an alloy obtained by the “LIGA” method, and in that it includes at least a first resilient arm (40) including coupling means (41) arranged for cooperating, in various coupling positions, with complementary coupling means (42) comprised in said felloe (5) to form, in the coupling position, a closed loop, the inertia of which relative to said balance staff (3) is variable according to said coupling positions.The invention also concerns a sprung balance or a timepiece incorporating a balance of this type.