Technologies tirox lightweight alloy steel rail this is an aerospace grade metal with a high resistance to traction and torsion well suited to the stresses of a performance saddle it offers a good alternative to carbon nack rails it has 7mm rail clamp diameter esd ergo shape design this is a refined saddle shape developed as a result of biomechanical studies done by prologo over several years esd saddles feature a slender front area and a short rear area that quickly reaches maximum