In order to create maximum speed of a distal segment or implement, the principle of the kinematic sequence (a.k.a kinetic link) shows that each body part, should accelerate then decelerate in a sequential manner. For the golf swing, to achieve maximum club speed, the sequence is pelvis, thorax (ribcage), lead arm, club shaft. This means that during the downswing the pelvis accelerates first and reaches peak first and then decelerates first, meanwhile the thorax is accelerating and reaches its peak then decelerates, but slightly later than and at a higher value than the pelvis; the same occurs with the lead arm, and finally the club, with the club reaching maximum speed at impact.
So this states that the pelvis slows down before impact in order for efficient transfer of energy to be achieved. But where or at what point in the downswing does that occur. It actually surprised me how early in the downswing this peak speed occurs. I reviewed many of the 3D swings in the TPI database and here are the results.