Starling Prototypes a New Kind Of Carbon Frame

Starling Cycles is practically synonymous with steel bikes, so it came as some surprise that they've developed a prototype to demonstrate a new type of carbon manufacturing. It's the fruit of a joint project with the National Composites Centre (NCC), Composite Braiding and Starling, all of whom happen to be based in Bristol, UK. Starling's founder, Joe McEwan, used to be a composites engineer in the aerospace industry, and despite being known for steel bikes, is far from a carbon sceptic. The trio secured £100,000 of funding from Innovate UK to investigate the use of braided carbon fiber using thermoplastic (rather than thermoset epoxy resin) for bike frames.

According to McEwan, the advantage of this approach is a product that's "tougher, repairable, re-useable, lower energy to manufacture, better manufacturing quality [and] much less environmentally damaging" compared to conventional carbon frames. Part of the study involved a life cycle assessment (LCA) comparing the environmental impact of thermoplastic to (regular) epoxy-based carbon frames, which found the CO2 emissions over the life of the thermoplastic frame to be significantly lower than the epoxy frame - though still much higher than a steel frame. It's worth noting this LCA was carried out by the National Composites Centre, not Starling themselves.


Thermoplastic carbon is nothing new. Guerrilla Gravity already use it, as do a couple of wheel manufacturers. What makes this project different is the combination of thermoplastic resin with braided carbon for use in a bicycle frame. Braided carbon is essentially a tri-axial weave of carbon, with full-length fibers running parallel and +/-60 degrees to the axis of the tube.

According to Joe, the braided structure and manufacturing process is a bit like a steel cable or the sheath of a climbing rope. That, he says, means there's less wasted material, fewer voids and other imperfections, less labour required (up to 90% less according to Composite Braiding, plus a lower scrap rate because human error is reduced and because it's possible to inspect the frame in the middle of the manufacturing process.


Joe is quite clear that true large-scale recycling of any carbon fiber is economically unfeasible because the energy required is high and the fibers aren't the same afterwards, but he says that it is easier to downcycle and repurpose this material than epoxy carbon fiber. He also says it's more resistant to impact damage due to the plasticity of the material and easier to repair because the thermoplastic medium can be heated and reformed.


But the idea is not to create a niche, expensive product for the eco-conscious few. The aim is to "develop a new high volume, low cost, high-quality manufacturing process for carbon fiber bike frames." By removing the need for laying up by hand and by eliminating a step involving the resin infusing into the fibrers, it should be possible to make a high volume of frames at a competitive price. That's the idea anyway.


The prototype they developed just happens to be an ebike frame, similar to the steel version we already reported on. It uses a Freeflow Technologies motor with a chainring on the left, which will connect to a drivetrain on the right via a jackshaft that runs through the middle of the high pivot, with a second chain connecting the motor to the LHS of the shaft. The bike has a steel swingarm (Joe says this still offers the best ride quality) with a machined aluminium motor mount to make manufacturing easier for a first attempt. Apparently, the lugs connecting the frame tubes together didn't quite work out as hoped, which means this particular bike probably isn't fit for shredding. Joe is hoping to partner with another manufacturing company to try and get production up and running at some point but not everything is worked out at the moment.

For more information, check out Starling's blog.

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