A bearing unit for a wheel hub assembly for motor vehicles, the bearing unit having an axis of rotation (X) and having two radially outer raceways, two radially inner raceways, two rows of rolling bodies, the bearing unit having tribological parameters whose values affect the magnitude of the frictional forces between the respective raceways and rolling bodies of the rows of rolling bodies, wherein at least one value of a tribological parameter is minimized or maximized to reduce the magnitude of the frictional forces as a function of the relative position along the axis (X) of a line of action (W) of loads acting on the bearing unit and of the plane of axial symmetry (Z).

In one aspect, a wheel end system is provided that includes a spindle having an interior and a side wall extending about the interior. The wheel end system further includes a wheel hub, inboard and outboard bearings rotatably connecting the wheel hub to the spindle, and a spacer between the inboard and outboard bearings. The spacer extends about the spindle and has a spacing between the spacer and the spindle. The side wall of the spindle has an airflow opening with an inlet portion that is outboard of the inboard bearing. The airflow opening is configured to permit air to travel from the spacing between the spacer and the spindle into the interior of the spindle.