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Is SRAM Developing a Wireless AXS Front Derailleur Built Inside Your Chainrings?

sram chainring coupled front derailleur shift
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On June 15th 2023, a patent filed by SRAM was published to the USPTO database detailing a wireless chainring-integrated front shift mechanism for a 2x drivetrain. Therein, the traditional front derailleur is replaced by a shift apparatus that is fixed to the chainring itself, moving as the chainring is rotated through each pedal stroke. That’s in great contrast to commonly available front derailleurs which, with the notable exception of the Classified Powershift Hub, are almost exclusively fixed to the front triangle.

Let’s dig into the proposed workings of this front derailleur that is housed entirely on the crankset.

sram chainring coupled front derailleur shift apparatus

SRAM Chainring-Coupled Front Derailleur

Before detailing how the chainring-coupled derailleur (for want of a better name) works, the SRAM patent in question (US 20200140035 A1) discusses a number of drawbacks associated with the current crop of front derailleurs. First up, as they are almost exclusively mounted to the seat tube, their mere presence forces constraints on frame designers, preventing them from getting too creative with frame shape for bikes that are destined for a 2x drivetrain.

sram force axs wide review

Then, there’s the shifting performance to consider. A traditional front derailleur is composed of two metal plates that push the chain inboard or outboard, guiding it to a larger or smaller chainring of the crankset, respectively. The SRAM patent says that this mechanism can cause rough transitions, which can become problematic under very high loads.

Also, tying the shifting mechanism to the seat tube effectively makes the front triangle a key component of the shift apparatus. If it flexes under high torque, or when the bike hits a bump in the road (think Paris-Roubaix), the position of the front derailleur will move away from its perfect position relative to the chainrings, putting the system at risk of misalignment with imprecise shifting as a result. I don’t really know how often that scenario actually causes issue, but the authors of the SRAM patent saw reason to point this out.

SRAM propose overcoming the aforementioned drawbacks with a new derailleur mechanism that couples the shifting device to the crankset itself. It reads, “The disclosed front shifting systems shift smoothly and consistently, even while under heavy chain loads… [they are] easier to install and set up than a traditional front gear changer or derailleur and do not require specific skills or training”.

sram chainring integrated front derailleur upshift downshift

How does it work?

SRAM’s Chainring-Coupled Front Derailleur concept packs all of the apparatus necessary to guide the chain from the big chainring onto the small chainring, and vice-versa, into the the big chainring itself.

In a number of the drawings, the internal workings of the distinct up-shift and down-shift components are out of sight. They are tucked underneath what the patent describes as an aerodynamic cover that may also serve as a structural component that brings additional stiffness to the system.

sram chainring coupled front derailleur shift

Of course, this is no mechanically-actuated shift mechanism. This is a wireless system, wherein up-shift and down-shift commands are sent from a bar-mounted remote – via Bluetooth or the like – to a receiver unit housed beneath that aero cover. Accompanying the receiver is a removable and rechargeable battery (purple) – that is similar in appearance to standard AXS batteries – a control unit, and a PCB. Visible externally, there is a button for pairing the derailleur with the shifter (blue), and an LED that could be used to indicate battery life (yellow).

Also underneath that aero cover is a motor and a series of drivers, links, shafts and pivots that are rotatably connected to one another in such a way as to force clockwise or counter-clockwise rotation of the up-shift and down-shift apparatus (Fig. 11). We won’t concern ourselves with the intricacies of that, only with the intricacies of how the chain is transferred from one chainring to the other.

Before we get started, pay attention to the architecture of the chainrings shown in Fig. 37 (above). Here, the chainrings are shown without the chain or any of the shifting apparatus attached. The structures labelled 264a-d are actually holes that allow for protrusion and retraction of the up-shift apparatus (seen in green in later images). And, very importantly, both the big chainring and small chainring appear to be missing one tooth, another characteristic that is essential to the workings of the up-shift mechanism, as will become clear.

Onward, and upward…

The Upshift Mechanism

Here, we will delve into the up-shift mechanism; how the chain is transferred from the small chainring to the big chainring. To kick off this explanation of the up-shift mechanism, we’re going to counter-intuitively start by looking at the elements of the downshift apparatus – 212a and 212b, shown in red.

sram chainring integrated front derailleur upshift downshift

When the chain is running on the small chainring, these two hooked arms are positioned over the top of the big chainring, taking up the space that the chain will accomodate once the up-shift is complete. So, it makes sense that the up-shift begins with the outboard rotation of these downshift elements away from the teeth of the big chainring.

sram chainring coupled front derailleur 2x drivetrain down-shift arms in upshift mode

The up-shift driver (yellow), and its connecting links (blue), are shown clearly in Fig.13. As the up-shift driver rotates counter-clockwise, the links of the mechanism pull the arms of the down-shift elements through a clockwise arc, re-positioning them clear of the teeth of the big chainring. That’s the first step, which is subsequently followed by the inboard rotation of the up-shift apparatus (green)… but only when the timing is right.

sram chainring derailleur front shift mechanism up-shift apparatus green

The up-shift apparatus (green) is only allowed to fall inwards, slotting the guide pegs (green) through the complementary holes of the big chainring, when the chain is clear of those holes, i.e. when the chainring has been pedaled into a position wherein the up-shift apparatus is in a rearward position, as shown in Fig. 41.

From here, the sequence of events is quite intuitive (below, Figs. 47-51). In all of the drawings, the small chainring appears to be missing a tooth. That space is filled by the first guide peg of the up-shift apparatus (green) when it rotates inboard. From here, it is able to catch hold of the chain, via the inner surface of an outer plate, as it is pulled through the pedal stroke.

sram chainring coupled front derailleur upshift mechansim guide pins transfer chain to big ring
Per revolution of the cranks, only one opportunity is provided for an up-shift
sram chainring derailleur concept frontshift integrated into crankset guide pins transfer chain from small to big chainring

Fig. 70 shows how each guide peg is strategically positioned such that each subsequent one sits slightly further outboard (radially) than its neighbor. The anatomy of those guide pegs is critical to the up-shift mechanism. Figs. 53 & 54 show how each peg (green) has a tip with a chamfered top surface (290) that allows the chain to slide down the peg, pulling it further outboard as it slides.

sram chainring coupled front derailleur up-shift guide peg anatomy contacts chain outer plate

During the sequence seen below in Figs. 47-51, the outer plate of the chain link (orange) that initially contacts the first guide peg is gradually moved away from the plane of the small chainring, and into the plane of the big chainring, with a final, larger up-shifting peg completing the transition. That up-shifting peg (320) then remains in position, thereafter functioning as a regular tooth of the chainring. The large plate (206, burgundy in some drawings) that sits outboard of the big chainring teeth acts as a guide to prevent the chain falling off the big ring in the outboard direction during an up-shift.

The Downshift Mechanism

Now, we take a closer look at the down-shift mechanism of SRAM’s chainring-coupled front derailleur, wherein the chain is transferred from the big chainring to the small chainring. This mechanism is not so different to how traditional seat-tube mounted front derailleurs guide the chain off the big chainring toward to plane of the smaller chainring.

sram chainring coupled front derailleur down-shift initiation

To mediate a down-shift, the linkage controlling the positioning of the down-shift elements (212a and 212b in Red) articulates about its various pivots in order to rotate the down-shift elements through a counter-clockwise arc. It moves from the position shown in Fig. 13, to the position shown in Fig. 46, re-positioning the protruding arms of the down-shift elements inboard, to the point where the top surface (338) overlaps the plane of the big chainring.

In conjunction with this rotation, the guide pegs of the up-shift apparatus are simultaneously retracted away from the small chainring and back into a dedicated recess within the body of the large chainring.

sram chainring coupled front derailleur down-shift elements positioned to initiate derailing of chain from big ring

Again, the timing is crucial. A down-shift element will only be able to rotate into the position shown in Fig. 46 when it is positioned rearward of the chainring. i.e. at a position where the chain is not engaged with the teeth of the big chainring – see Fig. 52. That’s because the presence of the chain on the teeth will physically prevent movement of the down-shift arm into its down-shift position.

sram chainring coupled front derailleur shift apparatus
Per revolution of the crankset, two opportunities are provided to execute a down-shift

When the downshift arm is free to rotate inward to a position where it overlaps the plane of the big chainring, it is then ready to de-rail the chain off the big chainring. As the rider continues through the pedal stroke, the chamfered surface (338) of the “leading” down-shift arm (212a) contacts the chain, deflecting it out of alignment with the big chainring, and into alignment with the small chainring.

After no more than half a pedal stroke, the chain is picked up by the small chainring. After a full revolution, all links of the chain will be engaged with the teeth of the small chainring, and the down-shift is completed.

Is the SRAM Chainring-Coupled Derailleur an Industry First?

SRAM is by no means the first brand to investigate alternatives to the traditional, seat tube-mounted front derailleur. Classified Cycling offer the most robust, proven solution with their Powershift Hub. By virtue of internal gearing packed away inside the hub of the rear wheel, the Powershift Hub is able to offer two distinct gear ratios for every single sprocket of the cassette. So, if you’re running a 12-speed cassette, you actually have 24 discrete gears at your disposal.

Classified Powershift Boost MTB 2x internal gear mountain bike hub for Shimano or SRAM 12-speed, Bike Connection Agency photo by Mirror Media, exploded view

Actually, this isn’t even the first time we’ve seen a company attempt to integrate the front shift mechanism into the chainring-crankset assembly. Vyro, a company that is seemingly no longer in existence, attempted to bring something similar to market in 2015.

vyro amen1 2x drivetrain crankset shift mechanism

The Vyro Am En1 cranks, aimed at All-Mountain and Enduro applications, featured a big chainring that was effectively segmented into four quarters, each able to move radially outboard independently of one another in order to allow the chain to fall from the big ring to the small ring as the rider pedaled the cranks through a full rotation. It was a neat solution that allowed the rider to shift under load, but in practice there were some real issues with its durability, and our EU Tech Editor, Cory Benson, had the misfortune of some key component failures while testing the system.

2023 specialized sirrus carbon x compliant frame strut
The 2023 Specialized Sirrus lacks the traditional seat tube necessary for the mounting of a front derailleur

Potential Implications for a Front Derailleur That Lives on the Chainrings

The solution proposed by SRAM is quite different to the abovementioned designs, yet still claims to offer better shifting under load than a traditional seat tube-mounted front derailleur. And, it should allow frame designers the freedom to re-shape the front triangle in the knowledge they no longer need to provide a structural member for the mounting of it.

For some unusual frame designs, like the Rondo Ruut 2.0 and the 2023 Specialized Sirrus, the implications are clear. While their lack of a suitably-positioned seat tube currently prevents them benefiting from a two-chainring crankset, SRAM’s chainring-coupled derailleur seems to be a reasonable solution.

2024 Rondo Ruut v2 all-new unique carbon gravel bike, interrupted seattube frame detail
Credit: Cory Benson – Bikerumor

There is also scope here for a big improvement in the aerodynamic properties of the drivetrain as a whole. Dependent on how well-executed that aerodynamic cover for big chainring is, this could result in markedly reduced drag as compared a front derailleur clamped onto the seat tube where it is very exposed, with the wind hitting it from all angles.

sram force axs wide review
SRAM’s current offering of a wireless electronic front derailleur – of the Force AXS Wide variety – isn’t exactly aerodynamic, or without its vulnerabilities; it also strikes us that removal of such a front derailleur could allow clearance for wider tires.

Certainly, there seems to be some good arguments for this new front shifting mechanism. On top of those already mentioned, this system would surely be much easier to set up than a traditional drivetrain, wouldn’t it? That said, we also foresee a number of downsides.

First up, shifting in either direction is likely to be slower than the shifting enabled by current front derailleur designs. Per revolution of the crankset, only one opportunity is provided for an up-shift, with two opportunities provided for a down-shift.

So, dependent on cadence, the rider could experience a noticeable lag in shift initiation as they wait for the shift apparatus to hit the right point in the pedal stroke. That compares to regular front derailleurs that can initiate a shift on demand, where the lag is effectively dependent on the ramps and pins of your chainrings, often providing 3-5 shift points per rotation on premium drivetrains.

Also, it appears as though it would be very difficult to execute a modular version of this system wherein chainring sizes can be switched up to the rider’s preference, and the gradients and elevation profiles in different parts of the world. We reckon the up-shift mechanism at least will be unique to a specific pairing of chainring sizes. That’s in contrast to the current crop of front derailleurs which offer some degree of adjustability to suit different chainring sizes and combinations.

Then, there’s the question of durability. As shown, large portions of the up-shift and down-shift mechanism will be exposed to moisture, as well as dirt and grime from the road surface. That’s the case with any derailleur of course, but this mechanism does feature a large number of pivots that are all at risk of premature wear if the system isn’t sufficiently sealed.

Also, those down-shift components are going to see a considerable amount of grime kicked up from the front tire through every single rotation of the crank, and I don’t imagine any of it will be a walk in the park to clean.

Finally, I do wonder how Q-Factor would be impacted by the housing of all that infrastructure on the big chainring. It seems possible the design could require a slightly wider Q-Factor, which may be an undesirable feature for some riders.

Similarly, for those prone to heel rub issues, the additional real estate packed underneath an outboard cover on the chainring could pose further issue with clearance throughout the pedal stroke. Certainly, the clocking of the components and their packaging would need to consider this very carefully.

Hypotheses aside, we’ll not be in a position to fully understand any of the above unless SRAM can, or even want to, execute on this design.

We have reached out to learn of their plans for this new shifting technology, but it’s a “no comment” for now. Of course, a patent serves only to protect the inventors’ ideas from implementation by competitors; it does not mean SRAM actually plan to bring this chainring-coupled front derailleur to market, nor does it necessarily mean they even have a working prototype.

I’m willing to bet they do, though. We think this is a cool idea from SRAM, and wouldn’t be surprised if they eventually brought this, or something very similar, to market over the next few years. Even if it never sees the light of day, it’s always super interesting to see what the brains behind the big brands are working on behind the scenes.

sram.com

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33 Comments
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joby
joby
10 months ago

Suntour and Browning tried this out in 1990 for any of you (we) grey hairs that remember….:

https://velobase.com/ViewComponent.aspx?ID=e86793a6-e84a-4bdb-8faf-fa02da8ec0ff&Enum=115

Joe
Joe
10 months ago
Reply to  joby

No, no, that’s completely different. It had THREE chainrings.

Ves
Ves
10 months ago
Reply to  Joe

hahahahahahahahahahahah

WhateverBikes
10 months ago
Reply to  joby

Came here to say the same thing. Even though that system had triple chainrings, it was much more elegant and simple than this overcomplicated contraption.

FrictionDi2
FrictionDi2
10 months ago

1x systems make sense. But I don’t think the front derailleur is such a problem that the industry is going to wild extremes to avoid it. I still think a wide low double 42/26 with a wide range cassette (11-40 or even just 11-36) is plenty of range. The industry is “innovating” with make things more complicated while selling it as being less complicated.

Kyle
Kyle
10 months ago

That patent was filed and reported on more than 3 years ago. Why write this article now?

Zach Overholt
Admin
10 months ago
Reply to  Kyle

This particular version was filed late 2022, and just published mid June. According to the application, it’s a continuation of the application from 2019.

Greg
Greg
10 months ago

Lots going on here. It would be nice if someone could animate it based on what is presented. The possibilities are real.
This system, like a traditional front derailleur, has inherent benefits over the Classified hub in efficiency due to chainline and from the lack of planetary gear systems. The main benefit of the Classified system is that it can be piggybacked on a dedicated 1x external drivetrain, giving you a wider range than you could typically get with a standard 2x system. Classified has other benefits over a the standard 2x, but this new system potentially overcomes those.

Tzvetan (Stan) Tzvetkov
Tzvetan (Stan) Tzvetkov
10 months ago
Reply to  Greg

It will work similarly to something I invented some years ago. You can see it here: https://youtu.be/uPrsBJQHEvM

WhateverBikes
10 months ago

Damn, that’s super nice! Did you ever develop it any further?

Tzvetan (Stan) Tzvetkov
Tzvetan (Stan) Tzvetkov
10 months ago
Reply to  WhateverBikes

Thanks for appreciating it! As I wrote, I thought the front derailleur is dead, so I did not develop it. I got a US Patent, though, and I filed it myself with no objections from the examiner whatsoever. I had another reason to abandon it: I came up with a new idea – a very unique and unusual gearbox with up to 72 different gears (ok, it’s an overkill, but you can limit it to 16). Working on it right now. Definitely trumps deraillers.

Andrei Kasaev
Andrei Kasaev
10 months ago

1x is great, the tech has grown up nicely.

That said, for road/touring it can be really nice to have closer spaced gear ratios.

That being said: FOR PETE’S SAKE… SRAM… just design a front derailleur that works well and live with it. Shimano and Campy did so. I feel like I need to bop them on the nose and say “LEAVE IT!”

Grooveninja
Grooveninja
10 months ago

SRAM had a 2-speed MTB crankset previously. Did anyone else have a Truvativ Hammerschmidt?

ranggapanji
ranggapanji
10 months ago

guys. guys. remember Hammerschmidt?

Frank
Frank
10 months ago

“in great contrast to commonly available front derailleurs which, with the notable exception of the Classified Powershift Hub”

There is nothing notably exceptional about the Classified Powershift. Rear hubs combining an external cassette (and derailleur) with internal gears have been done before. The external derailleur and cassette are like any other derailleur system; the internal gears are like any other planetary hubs made by Shimano, Sturmey-Archer, SRAM, Rohloff etc. Even the swappable core/body is not a new idea. Finally, Classified Powershift is not a front derailleur, so how can it be exceptional within a class in which it does not belong in the first place?

Last edited 10 months ago by Frank
WhateverBikes
10 months ago
Reply to  Frank

I agree that the concept is not new at all. What is exceptional about it however is that you can shift under full power and instantly. It’s also wireless (for better or for worse) and lighter than previous similar systems.

nooner
nooner
10 months ago

1x for life Bros!

Jack77
Jack77
10 months ago

Looks like trying to find an alternative for patented solutions like Shimano E-type and the Classified hub. In case there is a need for it (due to frame shape changes) and Classified cannot be bought by SRAM.

Strange that the article makes no mention of (rotating) weight. Nor the fact that it will probably be a case of “if it wears out, buy a new complete new chainset/derailleur combo”.

Stinky
Stinky
10 months ago

I’m not an engineer, therefore perhaps a stupid question – but why can’t the chainring be made to expand / contract instead? The chain can only be on one chainring at a time, so why can’t the chainring be designed in such way that it can expand from say 32 teeth to an equivalent of 44? Is the force on the chain and the chainring in such way and extent that it would inhibit such a mechanical expansion / contraction? Thanks in advance to anyone taking the time to answer my question.

Dann
Dann
10 months ago
Reply to  Stinky

Like the Husted transmission used on the Yankee bicycle?

https://bikenewengland.com/2018/06/10/radial-gear-transmission/

Ullulu
Ullulu
10 months ago

I’d love to see a 1x crankset with a mechanism to move the chainring sidewards in order to maintain a straight chainline.

Frites and mayo forever
Frites and mayo forever
10 months ago

“it should allow frame designers the freedom to re-shape the front triangle in the knowledge they no longer need to provide a structural member for the mounting of it.”

XTR BB mount FDs were good and a heck of a lot cheaper and simpler than all this.

Tim
Tim
10 months ago

Maybe so, but there is another limiting factor: rear wheels have grown 40mm or so in radius and also tires are wider than before.

Dann
Dann
10 months ago
Reply to  Tim

Also press-fit limits E-type compatibility

Tim
Tim
10 months ago

Surely I’m not the only person who has noticed that we are talking about a 2x front system?
I always thought front derailleurs were easy to install and adjust, that they shifted well, and that they allowed you to change your gearing ratio by a hefty percentage in a single shift. Those convictions have only grown over the decades as front derailleurs have gotten even better than they were back in the day, even if virtually no one rides them. I’m all for additional stripes on the tiger, but I don’t see how the system in this article is beneficial. Which doesn’t mean it’s without benefits- I could well have missed something.
Anyways, the big problem with front derailleurs is not that they work badly, but that they aren’t necessary or even useful for most people. Same goes for alternative 2x systems, except that people are not anxious to buy them.

Chad
Chad
10 months ago

Interesting – but thoughts:
– I need new chainrings = $$? for a set?
New chain (cheap) every 200 miles to avoid wear.
– 1x is “cool”, but no serious pro road team uses this alone – long live 2 chain rings.
– Wear – look at any road bike w/ 1x and you can tell where the rider likes to “hang out” on the cassette – 2 rings once again FTW.
– Sram – develop a chain ring that gets around Shimano held patents to reach Shimano A level bench testing standards (the gold standard). If TH Industries/FSA can do that surely you can crack that code (all about the patents).

Jason DW
Jason DW
10 months ago

The return of the Hammerschmitt!

Andrew
Andrew
10 months ago

Ok let’s see how they’ll mess up for this one too…..

JDR
JDR
10 months ago

typical SRAM, this is nothing more than another attempt to limit customers’ choices. If this thing makes it into production and OE , we are screwed. No alternatives, no other chains no other cranksets…you are forever stuck with SRAM. They have been doing this for a while.

jonathan
jonathan
10 months ago

SRAM will literally invent the most complicated mechanism ever introduced on a bicycle instead of just making a good front derailleur

Tim
Tim
10 months ago
Reply to  jonathan

Forsooth!

Dinger
Dinger
10 months ago
Reply to  jonathan

Devil we know. If everything were internally geared as we know it today and someone introduced derailleurs actuated by tensioned cables as an alternative, we’d all call them crazy. Same if disc brakes had come before rim brakes.

Doc Sarvis
Doc Sarvis
10 months ago

Amazing work in detailing this out. I sure do like my single mountain bike chainring though.

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