вот http://www.skimag.com/skimag/gear/article/0,12795,1091807,00.html
где в частности сказано:
The Pivot turntable heel was prized because its axis of release was directly beneath the leg's tibula/fibula shaft, where it was said to put less stress on the leg before release occurred. The knock against Pivot was that annoying lack of positive engagement: Step in, and its mushy, unemphatic snap left you wondering if you were secure. Not so with the new PX heel. The new heel snaps to attention with a crisp, eager "clack," and more important, its greater forward pressure yields noticeably better energy transmission.
То есть, новые пятки лучше "кликают" при защёлкивании и сильнее давят на носок