Abstract : The rheology of granular flows is the subject of many experimental and theoretical works. Previous studies of granular flows performed in rotating drums have shown that the velocity gradient in the free flowing zone is constant. We have experimentally tested the validity of this expression of the velocity gradient, for wider ranges of operation parameters that the ones that were used by now. For low rotation speed of the drum, we have shown that angles of avalanches and angles of repose could be geometrically similar if the particles used have size distribution or morphology that can be compared. At larger rotation speed, systematic measurements of flowing thickness and inclinations of the free surface showed different regime transitions. When the diameter d of the particles is large compared to the diameter D of the drum (small D/d ratio), the flowing thickness is constant and equals 1/3 of the drum radius. In that case, an increase of the drum rotation speed is accommodated by an increase of the velocity gradient. For high D/d ratio, the maximum velocity of the particles at the free surface first saturates. Consequently, an increase of the rotation speed is accommodated by an increase of the flowing thickness, thus, the velocity gradient decreases. This work has defined the limits of the field where a constant velocity gradient applies : neither the thickness of the flowing zone nor the maximum velocity of the particles flowing at the free surface should saturate. In a last part, segregation experiments were performed in order to make the link between flowing thickness and segregation of large glass beads in a small glass beads media.