New SRAM chains hint at new drivetrains , according to recent US patent applications. The publications shows some radically different chain design – though admittedly, it doesn’t take much for a bicycle chain to be considered “radically different”.
What sets one chain apart from another can be almost imperceptible. There’s width of course. Finish/color, along with cut-outs to shave a little weight. There are also subtle curves and dimensions that most of us are never aware of, but important enough to be patented. Still, swap a Shimano chain for Wipperman or KMC, and all still shifts fine. SRAM’s 12 speed flattop chain ranks as about the only stand-out, with its proprietary shape and roller diameter. We’ll leave DuraAce 10, and ancient oddball chains for another time.
It now looks like SRAM may be making even more new departures in chain design. Several recent patent applications show chains that eschew the conventional design that use pairs of parallel (inner and outer) plates. The patent drawings explain it best.
Some SRAM designs use “stepped” outer plates, as opposed to flat plates. That is, instead of alternating pairs of outer plates and inner plates that meet at a roller, the new design has only one type of plate, which has a “step” in it, so that at one end /roller it’s an outer plate, and at the other end/next roller it’s an inner plate.
As with many so many inventions, SRAM is not first with the general idea of a stepped sideplate chain. In fact, KMC was issued a patent on a similar stepped chain design in 2018. There’s also a patent application filed in 2004 showing the same. These are in some ways similar to BMX chains that use a half link. And I bet poking through the patent databases will show earlier examples.
More radical are the asymmetric chain links SRAM shows. To keep us guessing, they show several different type of asymmetric chain links, and show orientations in both inner and outer facing directions. These are unlike any prior art I’m aware of, so new SRAM chains hint at new drivetrains .
Years ago, SRAM’s Kevin Wesling (responsible for blue-sky product development possibilities) told me that chains are the centerpiece of drivetrain design. That is, the chain is the driver (no pun intended) of chainrings and ramps and pins and how many cogs will fit and how well a bike will actually shift. Start with the chain, then build parts that go with it. That’s surely because a chain is so constrained – there’s very little room to make dimensional changes, and minimum strength has some absolute requirements. I bet when chains went from eight to nine speed, engineers of the time said: “That’s it, that’s as narrow as we ever can go.” And yet we are now with 13 cogs out back. It’s the chain that allows that to happen.
So what’s different about this design from SRAM? The main thing is that SRAM builds entire drivetrains – they’re not just a chainmaker, or a hopeful garage inventor. SRAM’s new chain is designed to work with a pair of special chainrings that includes “deflector teeth” and “deflector recesses” for smoother front shifting.
The patent documents says the new chainlinks sing with the chainring in perfect harmony, every shift as crisp as dew-covered lettuce fresh from the garden. In fact the patent filings says nothing like that. Rather In the convention of such documents – and the intellectual property claimed – the description of the chain and chainrings is in thick language, a combination of legal and technical. It can be nearly impenetrable. For example:
The surface 94d-1 of the sliding bevel 94d is inclined in such a way that its normal vector NV has three non-zero Cartesian vector components, of which the axial vector component NVa is directed away from the starting chain pinion R11, the radial vector component NVr is directed away from the common assembly axis AO of the bicycle pinion assembly 86, and the vector component NVu extending in the circumferential direction is directed away from the trailing load-bearing flank 94f.
In practice, there may be several key advantages to the new chain designs. For the stepped links that the chain may be less susceptible to links popping apart and snapping under hard loading shifts. That’s because one end of each plate is an inner plate, and the other end is an outer plate, perhaps reducing the chances of an outer plate getting pried off and the chain snapping. Related, the improved inside/outside configuration can allow chains that are easier to open up and re-fasten. In fact, tool-less, snap–together links – and not shifting improvements – were the main goal stated in the similar KMC patent.
A second – and potentially game-changing — result of the steppe and asymmetric side plate design could be markedly improved shifting when going from a smaller cog/chainring to a larger one. When such a shift happens, it’s the outer plates of a conventional chain that get picked up by ramps/pins, and then teeth, to complete a shift. With conventional chains, half the links are outer plates, so only half the links are shaped to engage a shift. But with SRAM’s inside/outside design, every link can be shaped to engage pins/ramps/teeth – that’s twice as many points of engagement. In principle, that should result in faster shifts.
What’s the downside? Very likely, this chain and the drivetrain that goes with it won’t be compatible with existing chainrings and cogs. TBD of course, but it’s a safe bet.
In the claims of the patent – what define the intellectual property – SRAM is pursuing both a chain, and a bicycle drive assembly. Without diving into the excruciating technical nuances of SRAM’s design versus, say, KMC’s chain, the takeaway may be that SRAM doesn’t just make chains, they make bikes shift. And these new chains very well may show what we’ll be seeing on faster-shifting drivetrains in the coming years, as the new SRAM chains hint at new drivetrains. Indeed, contrary to perceptions, SRAM may not be all-in on 1x drivetrains for the future.
