Gemini calls their new Rigel carbon ring the “most technologically advanced chainring” to ever be made. And says it is “truly the lightest chainring in the world.” Crafted from continuous fiber ‘forged’ carbon over an aluminum skeleton, the narrow-wide 1x Gemini Rigel carbon chainrings are stiff, long-wearing, even aero, plus of course incredibly lightweight.
Gemini Rigel carbon 1x MTB chainrings
We’ve seen a number of carbon and composite chainrings over the years. I even made a full carbon chainring for my singlespeed mountain bike more than 2 decades ago that seriously outlasted alloy rings. Carbon lightness and stiffness have been promising in the chainring department. But none have really solved the issues of creating sharp & complex teeth from carbon that can handle varying chain angles, aid chain retention, and survive regular wear and tear. The most successful until now have resorted to making the outer ring of teeth out of various metals. And limiting the carbon to structural reinforcement or a lighter spider design.
Gemini crafts the Rigel direct mount chainrings mostly from carbon, but with alloy at the chain’s contact surface with the chainring’s teeth.
Who is Gemini again?
We mostly know Gemini Composites for their premium carbon mountain bike bars and 1-piece cockpits. Started in 2015 to develop advanced carbon MTB components by Roland Baides, a bike design engineer out of the Cero design studio. Baides became the chief design engineer for Unno for the first 2 years of the new mountain bike brand, before returning full-time to Gemini.
Now, situated in a small industrial zone a 1/2 hour up the coast from Barcelona – on top of auto repair & paint shops – Gemini combines their design and carbon production in a single combined studio and workshop. Everything from idea to components, made in-house.
How is Forged Carbon made?
Gemini’s secret sauce is multi-part construction, dubbed ‘Forged Carbon’, aka compression molding. First, a continuous aluminum ring of hollowed-out 7075-T6 alloy is cut. Then, they sandwich the toothed ring between precision-cut prepreg carbon discs, pressed inside a mold, and heated, under more than 100 tons of force to arrive at the final shaping.
The real secret is not entirely revealed – but is patented. The detail of how Gemini orients the fibers in the teeth. Based on our understanding of the patent, the pressure of molding squeezes the unaligned fibers (Discontinuous Fiber Composites similar to what we know as UD) in the precut carbon discs. This aligns the fibers concentrically (3 in Fig. 8-B), as they squeeze into the narrow channels of the teeth in the mold.
Gemini says the result is “an organization of continuous fiber structure in the tooth that is unattainable with traditional carbon fiber manufacturing processes“.
Out of the compression mold, there’s still plenty of hand finishing to clean up excess resin flash squeezed out. And to polish the finished Rigel ring.
According to Gemini, the resulting Rigel is the lightest Direct Mount chainring available. They claim a weight of just 39g for a 30T SRAM 3-bolt ring. “This is primarily thanks to the use of carbon fiber for both the structure and the teeth, despite having an internal metal core dedicated solely to extending its lifespan.”
The Rigel rings ultimately expose the edges of the inner alloy ring. That provides direct chain roller to aluminum contact, to transfer pedaling loads through the carbon body.
This means long-term durability against wear. At the same time, the carbon sandwich reduces friction, quiets the chain, and improves the overall aerodynamics of the system.
Gemini doesn’t explicitly state how many miles or kilometers you can expect to get out of their new carbon Rigel chainrings. But does advise cleaning & maintaining it like a regular ring – preferably using a dry chain lube. They also claim that real conditions durability is effectively similar to conventional aluminum chainrings.
All are manufactured in Barcelona, Spain right where they were designed and engineered.
Gemini Rigel carbon chainrings – Pricing, Options & Compatibility
The new carbon Gemini Rigel chainrings seem surprisingly affordable actually. OK, at 125€ a piece, they aren’t cheap.
But plenty of machined alloy direct mount chainrings already sell for 70-90€. This is officially cheaper than a stock SRAM XX SL replacement chainring. Even a heavier, non-DM Carbon-Ti 1x chainring made from a similar material mix will set you back 181€.
Gemini limits options to just three tooth sizes for the time being, each with Boost standard 3mm offset: 32, 34, or 36T. If you think you are faster than that, you’ll have to wait until Gemini develops bigger rings…
Gemini has been coy with the details, but suggested gravel-ready 38, 40, 42 & 44T rings will come “Soon“, as will a 52/36T pair. And they are also thinking of oval rings, and a version for SRAM’s latest thread-on ring-around-a-powermeter.
Compatibility is wide, though. Gemini makes the carbon Rigel chainrings in 5 direct mount interface standards – SRAM 3-bolt, SRAM 8-bolt, Shimano, RaceFace/Easton & Cannondale Hollowgram. That covers the vast majority of direct-mount MTB crank arms out there today. They are said to work with 11 & 12-speed drivetrains from Shimano & SRAM, including T-Type Flattop chains.
Get them now, direct from Gemini.