There have been rumblings of Shimano adapting clutches from mountain bike derailleurs over to their road groupsets, and now with the cobbled Classics underway that cat is out of the bag. Dubbed Ultegra RX, the new road derailleur combines Shadow+ chain tensioning tech and a long cage design to satisfy a wide range of riders from adventure road and gravel to cyclocross, all looking for a bit more chain security over rough terrain.

all photos courtesy Shimano

But it was actually the cobbled Spring Classics that brought the new derailleur into the light. As the derailleur was spotted this weekend in Flanders on the spare bike of Trek-Segafredo rider John Degenkolb, expected to race the new derailleur over the brutal cobblestones of Paris-Roubaix next weekend.

Ultegra RX Shadow RD+ clutched road bike derailleur

The latest generations of Shimano’s R9100 Dura-Ace and R8000 Ultegra groupsets had already started to adapt tech from the mountain bike. They already took both the lower profile Shadow shape that tucks the derailleur closer under the cassette (and more out of the way in a crash), and added the removable B2 upper link that brought with it Direct Mount hanger compatibility (and improved stiffness/shift precision.) So it wasn’t a huge leap to expect the clutch to make it to the road as well.

Cyclocrossers, both pro & amateur, had been the first calling for a clutched road mech. And some had even resorted to using a XTR or XT Shadow RD+ derailleur with road Di2 shifters, which would work for single ring setups. But with the growth of gravel, adventure road, and other drop bar off-road riding, it was time for Shimano to bring the latest mountain & road derailleur tech together.

Ultegra RX mechanical rear derailleur

Called an offshoot of the regular Ultegra road groupset, the Ultegra RX naming is for now just a chain stabilizing road rear derailleur for riding on rougher terrain. Designed to control derailleur movement over rough terrain, the Ultegra RX derailleurs get an On/Off switch for the tensioner located above the upper pulley. The RD+ stabilizer system looks like it is most likely a modified version of the lower profile clutch found on the XTR derailleur rotated 90° with its own unique housing, vs. the more modular clutch that shows up on the lesser mountain bike derailleurs.

The mechanical variant of the clutched road derailleur is probably the biggest deal for drop bar adventure riders, as it will offer reasonable pricing and compatibility with all of Shimano’s latest series of 11-speed road dual control levers (Dura-Ace R9100 or 9000, Ultegra R8000 or 6800, plus the new 105 R7000 or previous 5800 groups.)

There are already a lot of those groupsets out there, so simply swapping in this new clutched rear derailleur will be an easy upgrade to give your bike better chain retention over bumpy terrain. Weight claimed for the new clutched mechanical road derailleur is 248g, just 38g more than the standard Ultegra derailleur.

Ultegra RX Di2 electronic rear derailleur

Of course if you already have a Di2 groupset, the new Ultegra RX Di2 derailleur will now give you the improved Shadow+ chain retention, while allowing you to still use a road Ultegra or Dura-Ace front derailleur. Weight for the new Di2 version should be 287g.

Both new Ultegra RX derailleurs share a GS medium cage meant for cassettes topping out between 28 & 34 teeth. That means you can stick with the newest R8000 11-28, 11-30, or 11-32 options or the prior series HG800 in 11-34. Specs on the derailleurs say they can handle a total range of 39 teeth difference, with up to 16 teeth difference at the front derailleur, making them suitable for pretty much any road, road compact, or cyclocross double chainring combination that Shimano offers. You can maybe even stretch that out to an 11-42 with Wolf Tooth’s RoadLink DM replacing Shimano’s B2 link.

Pricing & Availability

Both of Shimano’s chain stabilized Ultegra RX rear derailleurs (RD-RX800 mechanical & RD-RX805 Di2 electronic) should be available through regular Shimano retail channels from the middle of June 2018. Retail pricing is set at $110/120€ for the mechanical derailleur, and $285/290€ for the Di2 version.


    • Innovative?! Where?! Shadow MTB derailleurs and 1X systems from Sram use this cage clutch concept for years!! I’m not even sure if this brings a real world benefit for “normal” road riding.

  1. A collective cheer just went up from the Triathlon crowd, many of whom have been wanting a Di2 compatible clutched road derailleur for 1×11 setups.

        • Yeah, there will be. Just as there is with every clutch RD MTB drivetrain. Take a friend’s MTB, put it in a stand, turn off the clutch and pedal. Do the same with the clutch on. There is a difference. I’ve even had customers comment on it. However, not really an issue unless you’re a pro racer at the top of their game. Or any triathelete.

          • No! There is no drag on transmission running. The drag is on the cage spindle to virtually inhibit the cabe from whip on rough terrain. Can’t really understand why we would need it on a 2X road transmission.

    • you don’t need a clutched RD for road at all, especially tri, just use regular RD and narrow/wide rings – been on eTap 1×11 for over a year zero issues with chain retention 6000+ miles

      • Did everyone else see Wout Van Aert lose his chance to contest for the podium at Paris Roubaix today because his chain derailed in one of the late cobble road sections. Irony: he uses SRAM components…

      • Chainslap. If you put a big cassette on like a 40 tooth or so when you’re in the higher gears and you stop pedaling the chain will slap because of the rotational weight of the large cassette.

      • Ran on Shimano mtb shifters for more than 2 decades and never had problems with chainslao making it came off. We have to understand that this is a very aggressive market and makers need to be constantly giving us “new” features. They constantly give us things we don’t need. The biggest of them all are 29rs. What can we do rather tal following what market has to offer?!

  2. I’d love to say I’ll sell a thousand of these.
    But really I’ll just install a thousand of these purchased off Merlin cycles…..

    • Well, in Shimano’s defense SRAM doesn’t actually have a clutched 2x rear derailleur for road. It’s true that you can run the GX 11-speed 2x derailleur with a SRAM 11-speed road shifter, but it’s not technically designed as such.

      • True, but the throw is the same on road/mtb derailleurs, at least for SRAM. For years I’ve use the SRAM XO short cage (which works up to 36t cassette) w/ a clutch on cross/gravel bikes with Red22 hydro with no issues. For gravel, I use 52/36 w/ 11-34 cassette.

        Anyone want to wager on the SRAM 1×12 hydro road group being out before July?

      • You can’t run a gx 11sp rear mech with an 11sp road shifter, they both have 1:1 actuation but cable pull is not the same for road and mtb. I tried and ended up ordering a shiftmate adaptater pulley to make it work

      • Sram have clutch rear derailleurs for the road that with work 2x. Just because it is called apex 1 doesn’t mean you can’t still run a front derailleur.

        • You can’t run a SRAM x1 RD (the “X-Horizon type”) with 2x. The offset of the upper pulley is what sets the pulley’s distance to the cassette cogs. There is no sweep angle built into the parallelogram links. When you shift from the small to large ring on the front, the swing of the derailleur cage throws the pulley to cassette clearance right out the window.

  3. OTOH, unlike SRAM, you’ll be able to run a double crank and an 11-34 cassette without resorting to mutant MTB/road drivetrains.

  4. Not surprised to see this; rumors I’ve been hearing for the past few months indicated a clutch derailleur at the 105 or Ultegra level… but the rumors also indicated a subcompact crank. I wonder when that’s going to be released?

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