Which part is most commonly classified as unsprung weight on a live axle suspension?

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Unsprung weight is the portion of the vehicle’s mass that the suspension does not actively support, so it moves with the wheel over bumps. In a live axle suspension, the body and the main suspension springs carry the load, but the mass inside the axle assembly itself—the differential—sits between the wheels on the axle housing and moves with the axle. That central mass isn’t supported by a separate spring or the chassis in the same way the sprung mass is, so it contributes most to the inertia the wheel must overcome when the road surface changes. The differential is the heaviest single component in that area, making it the typical example of unsprung weight on a live axle. The brake components and wheel are also unsprung, but the differential’s central location and size make it the dominant unsprung mass. The leaf springs and sway bar are part of the sprung-side suspension, so they’re not classified as unsprung weight.