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.
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.
