Fizik Kurve Bull Saddle, for Medium Spines - Mobius Rail, Black Bull: Those with less flexibility are not able to easily accomplish the high performance cycling position. To reach this position the pelvis rotates forward dramatically forcing the hips back. Wing Flex: shell flexes downward where the inner thigh contacts the saddle allowing more efficient pedalling and full-range movement Twin Flex: Kevlar/carbon shell is bonded to a stiff outer shell and provides a hammock-like feeling; sweet spot for pressure distribution in the perineal region Mobius Rail: a circular rail construction eliminating pressure points and providing flex Interchangeable tension system allows riders to customize saddle flex by changing the nose piece