SRAM electronic drivetrain patent application drawings for road and mountain bike groups with wireless options

First spotted in the wintry cold of midwestern cyclocross races, SRAM’s electronic drivetrain has resurfaced on the road race scene. And we uncovered this patent application that provides a solid idea of what they’re working on. As with any patent, the scope is likely intentionally broad to cover all options, so not everything you see here will necessarily make it into production. But, it’s pretty interesting, and shows what could be the first modern wireless production drivetrain.

Actually, there are two patents at play. The first was filed in 2011 and published in March 2013 with mention only of an electronic system where “each hand is only required to operate one switch to shift the bicycle”. The second throws wireless into the air – here’s the abstract:

The invention provides a wireless control system for a bicycle, including at least one shift actuator generating an input signal when actuated and a master control unit transmitting a shift signal responsive to the input signal. At least one electromechanical gear changer is provided and includes a gear changer control unit. The gear changer control unit receives the shift signal from the master control unit and controls the at least one electromechanical gear changer corresponding to the received shift signal. The gear changer control unit listens for the shift signal during a part of an awake mode cycle time, the master control unit transmitting the shift signal for a message duration time which is greater than the awake mode cycle time.

Now, let’s look at the details…


SRAM electronic drivetrain patent application drawings for road and mountain bike groups

The big question is, how is SRAM going to do something different than Campagnolo and Shimano. Well, it all starts with the shifters…and, literally, the first couple paragraphs of their patent application which describe the “deficiencies” of having four buttons to use, one each for up- and down shifts for both front and rear mechs. It says the abundance of buttons leads to unintended shifting and requires too much thought to use properly. How we’ve managed so far is beyond us.

Thus, their invention allows both front and rear derailleurs to be shifted using only two switches (aka: buttons, shifters, levers, etc.), and those are situated so only one hand is required per switch. In other words, the right lever shifts one way, the left lever shifts in the other direction. And that seems to be the case for shifting the rear derailleur. One goes up, the other goes down. And if you hold one button down, a shift “will be executed after an elapsed time, without the need to release the switch.” So, yes, multi shift outta the box.

SRAM electronic drivetrain patent application drawings for road and mountain bike groups

To make such a system work with a front derailleur also, you’d need a way for those switches to send different signals than the up-or-down movement, and here’s where it’s brilliant in its simplicity. Just push both buttons at the same time.

SRAM electronic drivetrain patent application drawings for road and mountain bike groups

Since the front derailleur usually only needs to go between two positions, and since Position Sensors and control units appear to be in each derailleur, it knows that a signal simply means to switch positions. The patent paper clearly states that accidental front shifting is greatly reduced because two switches need to be activated concurrently, which all but confirms this is how it works.

All of the thinking is done by a separate control unit, which interprets the signals sent from the levers and sends the appropriate command to the appropriate derailleur. The control unit would also know if there were no front or rear derailleur and adjust accordingly (i.e. 1×11 cyclocross bike, etc.). What’s particularly interesting is the specific mention that it’s possible the Control Unit (28) could located off the bike, such as a “wrist or in a jersey pocket” and that the communication link “could include wires or be wireless or be a combination thereof.”

How and where the actual gear control electronics are placed remains to be seen, but options (shown above) include putting most of it in the Control Unit or dividing it up with bits in both derailleurs. Theoretically, the more you put into the derailleurs, the less you’d need a separate box, but costs of those units would likely go up too much. And most of the spy shots show a separate box under the stem.

There are paragraphs of technically complicated lawyer speak about circuit timing and checking, all of which can be summed up to say this: It’ll check itself against trying to shift the rear derailleur while also wanting to shift the front and make the best of your mangled instructions to shift both at about the same time if that’s what you really want to do. How that works on the pavement will be very interesting to see, but sounds like you can tap the opposite button to shift the front while multi-shifting the rear.

And that bit about multi-shifting? It’ll most likely be programmable to your liking (on/off at the least), and it also hints at the availability to make the system work with a triple front chainring. Shifting from the smallest or biggest chainring is easy, there’s only one way for it to go. But, in the middle chainring, the Control Unit would pull current gear information and combine that with speed, acceleration, torque from a power meter and/or other information to figure out which way you probably want to shift. Or, it could be programmed to shift in the direction of the button you pressed first – as in, hit the right button a fraction of a second before you hit the left and it’ll shift to the specified chainring. Reverse the action to shift the other way.

SRAM electronic drivetrain patent application drawings for road and mountain bike groups

Heh, heh. Mountain bike.

The position of the shift units can vary, and the paper mentions bar end (TT) shifters, top mounted flat handlebar buttons and the drop bar buttons shown in detail. It also mentions multiple positions, putting pairs both on the brake lever housing and bar ends. The button placement isn’t even limited to a lever behind the brake lever. The detail photo of the drop bar shows an alternate placement (52) on the hood structure. They even mention it could be actuated by moving the brake lever itself inward. Basically, nothing’s off the table if it makes ergonomic sense. And the actual signal type is left open, too, suggesting “optical” (likely meaning fiber optics) or other methods are possible. Yep. Wiiiiiiide open.

SRAM electronic drivetrain patent application drawings for road and mountain bike groups

For the rear derailleur, the motor and gearing is at the rear (144, 106). These original drawings show the front derailleur’s motor (104) underneath the parallelograms, but we’re guessing clearance on too many modern frames with oversized, irregularly shaped seat tubes forced it’s placement on the top.


The complete bicycle diagram at the top of the post comes from SRAM’s wireless patent application, which was filed in 2012 and published on April 17, 2014. As with the wired version, SRAM’s paper outlines the need for a “highly reliable and more secure wireless control system” for bicycles, citing other applications that use an “always on” (kills battery life) or “low power transceiver” (poor signal strength) or “periodic beacon signal” (also kills battery).

Their application intends to solve these issues with a high power transceiver (good signal strength) that cycles on and off (saves battery), apparently using a very, very quick “wake up” signal at the sign of any button push that immediately gets things listening and moving. Actually, the receivers are in a very low power “sleep” mode, letting them still catch incoming signals, but the transmitters are off to save power. When a signal is received, shifts happen, then things go back into the low power state. A “wake” signal could also come from third party devices or other equipment (vibration or motion sensors, speed/cadence magnet, etc.).

The other concern is cross talk in a peloton. You wouldn’t want your buddy’s shifter moving your derailleur. For starters, each part of the system is paired to the other. Then, each derailleur (or a Master Control Unit – MCU) listens for “noise” and compares that to the signal it’s paired with and effectively ignores anything else. The shifter’s transmitter sends multiple signals for each shift command, essentially confirming and reconfirming that you actually want to shift. The derailleurs/MCU listens for this repetition before shifting. All of this is likely happening in millisecond time periods, so lag should (hopefully) be imperceptible.

A final precaution against interference is that the receivers can listen for other transmitters that aren’t paired to your system, then wait (again, milliseconds. As in, like 3ms to 9ms.) to transmit its own signal until the air is clear. It can also randomly change it’s transmissions’ frequency of repetition (+/-1ms) or the lag between each burst to further differentiate itself from nearby systems.

SRAM electronic drivetrain patent application drawings for road and mountain bike groups with wireless options

The lever diagram above shows two additional parts compared to the wired version – Trim adjustment (56) and a battery (46). The patent shows two iterations for a complete system. One is with batteries in each shifter and each derailleur, with each individual component housing all of its own electronics, memory, transmitters, receivers, controllers and power source.

The second shows two MCUs, one connecting the shifters and holding the battery/transmitter/receiver for both of them, and the other MCU housing the equivalent parts for both derailleurs. The latter would certainly make charging a bit easier!

SRAM electronic drivetrain patent application drawings for road and mountain bike groups with wireless options

Other changes from the wired system are largely programming related, like sending a “button released” signal to the derailleurs/MCU so it knows a shift is finished. This one’s another safeguard against misshifts caused by adjacent bikes – if the derailleur/MCU never received the “button pushed” signal, then it knows to ignore the “button released” command.

SRAM electronic drivetrain patent application drawings for road and mountain bike groups with wireless options

It can also build in an automatic trim position for the front derailleur (theoretically, so could the wired version, but it’s mentioned here specifically), letting it fine tune it’s placement in relation to the chain’s position on the cassette.

The shifting method and process for changing the gears in the wireless patent is quite brief and largely mirrors the process in the original patent for the wired version.

SRAM electronic drivetrain patent application drawings for road and mountain bike groups with wireless options

Shown here as a self contained unit, the battery sits at the back of the derailleur (62) and is perhaps what all that extra space is at the back of the spy shots we’ve been seeing.

In all iterations, the derailleurs/shifters or MCUs have LED lights to indicate status and, likely, assist with pairing. The patent mentions both ANT+ and Bluetooth Low Energy (BT 4.0). It also mentions that data on speed, gear ratio, gear selection and more can be received by devices like computers, smartphones, etc. And it definitely doesn’t rule out having things controlled by a separate device, either.



These photos are screen grabs from Global Cycling Networks’ video from the Amgen Tour of California. Check out the video and their YouTube channel here. Hat tip to for the vid link.







  1. Ck on

    Colin: It’s being reported that the left paddle shifts to a bigger cog, the right paddle shifts to a smaller cog, and pressing both at the same time changes chainrings.

    And just to put a positive comment in before the tidal wave of hate and criticism, i’m excited for electronic SRAM, wireless or not.

  2. Mike on

    I have no hate for SRAM, but plenty for the US Patent Office. I really hope this patent is not awarded but I’m sure it will be. The lightbulb was an invention, so was the telephone. A slightly different layout of buttons is NOT an invention.

  3. Gunnstein on

    I was initially sceptical since wireless means 3 or 4 batteries to charge rather than 1, but if well implemented I guess the hassle is minimal. I assume the trigger batteries at least will last quasi-forever and may not even be rechargeable, perhaps a CR2032 is all it takes.

    Glad to see that triple cranks are considered from the start. Even Shimano isn’t there yet. MTBers, tourers and even some commuters will want in on this eventually, so better get it ready.

    Hope that autotrimming of the front derailer can be disabled, for nonconventional frames where it isn’t needed.

  4. Gunnstein on

    Sometimes simplicity harms usability. Not sure I like the two-button setup. With this you cannot for example do rear shifts with a bottle, or camera, or whatever in one hand. Well you can, but in one direction only. Perhaps not an issue when one gets used to it, but usability seems better with a conventional two buttons per hand. Also no fallible heuristics needed for triple cranks.

  5. Bas on

    Ok, SRAM definitely wants us to hop on the 1x bus… With such front shifting logic, I’d rather ditch the FD. Like the idea of seq shifting, though. My Di2 is sometimes too sensitive for my bulky fingers. Wireless would be cool, a WiFiWiFli something

  6. Wendell C on

    Well that is certainly different. A system like this seems super ready for user error however. What kind of “buffer” does the double-press motion have? Said buffer would likely make any rear shifting pause a second before the actual up/down motion. That would be very frustrating.

  7. PotbellyJoe on

    If it’s going wireless, why even put it in the brifters?

    Put it in the gloves on the side of fingers. then you can shift no matter where you are seated, or how you’re positioned.

    Now that would be an invention.

  8. Hotep on

    More innovation….Need to mechanism that captures the output energy (hubs, BB, pedals) generated by a cyclist and feeds it back into the battery system (obviously with negligible resistance) so you’ll never need an outlet. Similar to a bike light dynamo system. Oh, and in Hotep’s fantastic dream world and it’s feather light too.

  9. Sizzler on

    Clearly this should be some sort of Nintendo Power Glove type devise where the controls are located on the right wrist to allow for one-handed shifting.

  10. aaron on

    still do not want my bikes to NEED a battery. (yes have ridden Di2, but still not sold on requiring a battery to change a gear.)

  11. Frank on

    Which is easier…charging a battery periodically (or batteries in this case) or having to replace shifting cables every season? Electric shifting isn’t affected by cable contamination, cable friction (tight bends on small frames and TT bikes), and shouldn’t need adjustment once set. The new shifting method also appears simpler which is always a good thing. If they can eliminate cross-talk and other electrical interference, then I think they have a winner here. I would also expect it to be significantly lighter than Di2 or Campy EPS.

  12. dukeynz on

    A minor (and picky) point, lawyers dont normally write patent specifications, patent attorneys do (and it they are dual qualified they are normally wearing their patent attorney hat). The distinction is small but important, kind of like the difference between a mechanic and soigneur on a team – to the outsider they just look like members of the team support, but in practice they are quite different.

  13. dukeynz on

    Also, it wouldnt be too hard to make this autoshift the front and rear for you based on you simply pushing one leaver for harder gear, other for easier gear, knowing the front ring sizes and the cluster range it could do it quite easily. What becomes a little more difficult is when you want to shift a large range quickly, eg dumping front and climbing rear fast…

  14. Pete on

    I’m pumped for this to shift to the MTB market where shifting under load is far more common. To me the ultimate benefit of Di2 systems is the lack of issue when shifting in this manner. How many times have you been caught out by a short steep climb and not been in the right gear? With mechanical shifting, you either tough it out in the gear you are in, try to pull off a tricky unloaded shift, or crunch through loaded gears and knock a couple hundred miles off your chain.

  15. Tom on

    Wait so four buttons is far too complicated, but having to synchronise button pressing is not? I am very keen to get some hands on time with this.

  16. bazookasean on

    I would think that SRAM could still have double tap. Push the paddle once for upshift, push it through that shift to a slightly harder click to downshift. Both sides could do this. Then push each paddle once to shift the front mech. you could shift the rear with either hand. you would need both hands to shift the front, though. That sounds like 4 buttons to me.

  17. muf on

    Meh electronic is cool and all but mechanical shifting is plenty fine, i dont like to bother with charging the bike all the time.
    You di2 users, why do you use that? Cause cool and new or howd u really like it.

  18. Steve J. on

    You should charge wireless, (as some already, with some smart phone is feasible), intigrieren for the batteries, so you would have no cable or charger use. The defend a very large Inovation for electronic circuits.

  19. Beancouter on

    I like the way the first graphic has a traditional frame (e.g. quill stem) and an exogram chainset!

    Always like a bit of new technology, although would prefer they focused their efforts at getting me my replacement hydraulics….

  20. CXisfun on

    @muf: “i dont like to bother with charging the bike all the time.”

    Have you owned a Di2 bike? I do. Three actually. Wanna know how often they need to be charged? I get about 2000-2500 miles on a charge, since I have three bikes and rotate pretty regularly, I charge them all at the same time about twice per year.

    How often do you charge your cell phone? Or your laptop? Do you really think twice per year is “all the time?” Because if you do, batteries in any capacity probably aren’t for you.

  21. K11 on

    @CXisfun. obviously you’re are a Di2 fan. I am very much “neutral” on these systems. I had a chance to demo a Di2 shop bike for a while, honestly it does work really well. I guess moving forward with my frame i am having built, decided to go shimano’s mechanical/hydraulic disc system. Just don’t want my bicycles to have a battery shift system, at this point. I think there will be dramatic refinements over the next couple years that will make me join in on my next frame.

  22. WannaBeSTi on

    Burnt, thank you for taking your comment in a different direction. I thought you were going to say something about using your gentleman sausage to shift. Which makes me think “what would the women’s trouser shifter be?”

  23. k on

    not a fan of electronics but anyone who thinks mechanical holds a candle to DI2 is in a dreamland. and i am a huge sram guy.

    looking forward to doubleclick!!

  24. Psi Squared on

    @k: do you have any objective evidence to support your idea that Di2 is objectively better than mechanical gruppos?

  25. John on

    On a compact double, because the ratios between 50t and 34t are so wide, an upshift to the big chainring is matched with a downshift to a larger cog, or a downshift to the small chainring with an upshift to a smaller cog.

    How the hell will you do that simultaneously with this new SRAM doubletouch system?

  26. Flip on

    @Psi – As always, you are being needlessly literal and pedantic. The user k simply expressed an opinion, which does not require objective evidence. Asking him for such is boring and arrogant, and typical of your posts.

  27. Kirkcapo on

    I am a bike shop owner and head mechanic. I do road, CX, MTB, and Tri race builds. I do dream bike builds too. When a racer wants the fastest shifting this season, it’s electronic hands down. Di-2 is more mechanically robust than EPS, but like mech ergonomics, most agree that EPS is more refined (lever shape, braking force relative to effort at lever, improved thumb lever position, etc). Dream builds involve a slightly more complicated criteria. Is it this years dream or a lifetime build. I continue to replace index springs and carriers in Campy shifters as old as 8 speed and they feel fresh as new after $25 worth of parts. I replace 7700 and lately 7800 shifters more and more frequently because they are “used up” and not rebuildable. SRAM is tough stuff and my personal choice for CX, but refined is not a word I would use to describe SRAM groups. Snappy is a better description. Race build – Di-2. Dream build, EPS if you don’t mind seeing obsolescence coming, mech if you want your group to last forever.

    SRAM if you want the lightest but don’t mind being a product tester as an early adopter.

  28. gabbia on

    Let’s hope their engineer for this is at least a little better than their hydraulic brake engineer!
    SRAM’s been scary lately with their recent stull.


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