Prologo Zero-II Saddle with Tiro X Rails: Prologo Zero-II Saddle with Tiro X Rails. A flat saddle for short to medium distance riding where a frequent change in position is necessary. With Tiro X rails & carbon fibre injection base. Tiro X Rail Rail light-alloy steel, this material is highly resistant to traction, & torsion for its light weight its for these reasons it is used in used in the aviation & aerospace industry. Tiro X then turns out to be a rail with a good balance between weight & strength, that doesnt fear the normal stress that addresses a bicycle. Carbon fibre injection base Tiro X rails Light PU padding Road use Flat profile suitable for short rides with frequent changes in position.