SRAM has filed a patent for a half-link style chain for use in a traditional derailleur-operated drivetrain. First covered by Escape Collective, the patent indicates that the SRAM engineers are tinkering away with a new drivetrain that could shift twice as fast as anything they currently offer.
All multi-speed drivetrains from SRAM, Shimano, Rotor, MicroShift, KMC, Campaganolo, FSA, and Box currently use a chain design that has two distinct plates. A set of outer plates alternates with a set of inner plates to give a chain that has an alternating width tooth space. Without exception, when shifting from a smaller cog to a larger cog, it’s the outer plates that ‘catch’ onto a tooth of the new cog to initiate a shift. The new chain design proposed by SRAM aims to double the speed of shift initiation by making every single plate in the line of links capable of catching the tooth on the new cog to initiate a shift.
The design centers on the use of a single plate type, with a step along its length that allows it to simultaneously function as both an outer and an inner plate.
The concept of a half-link chain has been around for decades, in use on single-speed drivetrains like those seen on a BMX. The half-link design has shorter links, allowing for finer tuning of actual chain length, something that is more critical on a single-speed setup where there is no derailleur there to maintain correct chain tension. What’s most interesting with this patent from SRAM is the use of the half-link design on a traditional multi-speed derailleur-operated drivetrain.
The patent largely focuses on the chain design, but the design of the chainrings and cassette it could be paired with are also mentioned, along with terms like “deflector teeth,” “deflector recesses,” and “non-zero Cartesian vector components.” An explanation of the latter you will not find herein, but I mention these things here because again, it suggests that SRAM may be developing an entirely new drivetrain with new shifting architecture.
It could be that they are turning their attention back to the 2x drivetrain, having neglected it relative to the 1x drivetrain which has seen huge developments over the last decade. Many reviews have mentioned how Shimano front shifting is a little faster than SRAM’s front shifting; it is possible that this design represents one of SRAM’s more creative ways of tackling that particular problem, while bringing other benefits to the table at the same time. I imagine that manufacturing a half-link chain is more economical than the manufacture of a regular chain, owing to there being just one plate type.
While the proposed design may have implications for future 2x drivetrains for road, it’s entirely possible this design could offer benefits off-road, too. It can’t be ignored that the patent actually depicts a full suspension mountain bike, not a road bike.
There are now seven mountain bike variations of Transmission – SRAM’s full-mount derailleur, flat-top drivetrain design. All are 12-speed affairs; five are wireless electronic, and the two latest ones are mechanical.
What’s missing from the SRAM Transmission lineup is a DH-specific version. Their 7-speed XO1 DH drivetrain that was released over 10 years ago still relies upon a derailleur hanger. With the vastly-improved impact resistance of the full-mount derailleurs over hanger-hung ones, I fully expect SRAM to eventually deliver a DH-specific Transmission.
Will it utilize this half-link chain design? It’s impossible to say of course, but faster shifting should be beneficial across disciplines. Another thing to note: unfortunately, chain breakages are still not uncommon at a UCI Downhill World Cup. Several runs per year will see a chain break, usually as a rider hams on the pedals down the start ramp. If the half-link design can handle more torque before popping a roller, then perhaps it is worth pursuing.