The Formula FX uses SDG’s I-Beam mounting system, with a single rail forming a single moulded piece with the nylon hull. The design was originally devised to get around the problem of conventional saddles popping rails under hard use but has found its way into more cross-country oriented seats too.
You’ll need an SDG post – having to buy into the whole system is a real drawback, though you can get a version of the Formula with normal rails. The proﬁle’s similar to SDG’s Bel Air, but the nose is less droopy. The sides sweep out closer to the nose than most saddles, but they’re also deliberately ﬂexier. Hull ﬂex is limited and there’s no pressure-relieving channel on top – if you like your saddles ﬁrm, give this a go.