The two-piece wheel rim assembly includes first and second hub sections affixed together and rotatably mounted on an axle by a set of bearings which are longitudinally spaced apart on the axle. The hub sections have radially inboard wall segments and radially outboard segments. The inboard segments form a radial cavity about the axle longitudinally bounded by the bearings. An oil bath substantially fills the radial cavity except for a small thermal expansion air pocket. The thermal expansion air pocket is positioned above the axle and the bearings when the hub-tire combination is in use. The thermal expansion air pocket has a nominal size only sufficient to account for thermal expansion and contraction of the wheel.