Check out the Filament FX bike with no down tube or chainstays

The Filament FX is an interesting bike with a story to tell; this carbon-fibre epoxy composite frame is made by hand in the UK, creator Richard Craddock saying that it was inspired by “the maverick frame designs of the 1990s”, but it's designed  for use with modern features, like disc brakes, thru-axles, internal brake lines, and tyres up to 32mm wide.

Wow! There’s a lot to unpack here. This is a very unusual bike; not the sort of thing you’re going to see in the window of your local Halfords. Let’s start at the beginning... Filament says that the FX takes its inspiration from Graeme Obree, Corima Fox, Trimble, Alpinestars, Hotta, Lotus, Metron, and others who explored alternative frame designs.

The vast majority of bikes are built around ‘double-triangle’ designs: a front triangle (which usually isn’t actually a triangle) formed by the top tube, seat tube, down tube and head tube, and a rear triangle (in fact, usually two of them) comprising the seat tube, seatstays, and chainstays.

There have been many exceptions, though, such as Graeme Obree’s Old Faithful, which he rode to massive success in the 1990s, and many carbon-fibre monocoque frames, such as the Lotus and Hotta bikes ridden by the likes of Chris Boardman.

The UCI eventually brought in rules to outlaw non-double-triangle frames for racing, but not before many people had experimented with unorthodox designs. It’s these bikes that Filament is thinking of with the design of the FX.

You’ll notice right away that the FX lacks a down tube and chainstays. Instead, the frame is built around a central strut that is effectively a top tube and head tube combined, and this runs into the seatstays, with a seat tube (of sorts) extending up and down from the middle. It's a long way from conventional.

Essentially, Filament has reduced the number of frame elements. Why? For a clean look and a smooth ride quality, it says.

“It's an exploration of some of the alternative frame designs we saw in the 1990s before they were ruled out of racing by the UCI,” says Richard Craddock. “This particular creation is inspired by Graeme Obree's bikes, including the paint choice.

“The intention is to increase the comfort of the ride, with more vertical compliance to smooth the bumps.”

Richard says that building a frame without these usual elements presents challenges in terms of managing the load paths and maintaining enough vertical stiffness. Gear cabling is also an issue on a bike of this kind, so wireless shifting is ideal.

The Filament FX is made from carbon fibre epoxy composite with a structural internal core. That core is a material called Rohacell, which is a polymethacrylimide-based structural foam. 

“The core makes it much more resistant to crush forces compared to being hollow, so accidental damage is reduced,” says Richard. “It also increases stiffness.”

Each FX is custom-made by hand in the Filament workshop in Bromsgrove, Worcestershire. Richard has been making frames for the past 12 years after working for other companies and manufacturers in the bike industry.

Take a look at Filament’s tube-to-tube construction methods here. 

“The rigid core material is cut and shaped, then the prepreg carbon is wrapped over,” he says. “The core supports the skin and distributes the forces as with the lattice structure used in 3D-printed metal parts.”

A Filament FX frameset (frame, fork, headset and seat collar) is priced at £6,000. Filament also sells full bikes; it offers an individual service.

The Filament range also features more traditional-looking frames for road, gravel, time trial and track, plus tandems. The designs are diverse although they’re all available in custom geometries with custom paint finishes.

Find out more about Filament.

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