Shimano Ultegra RX Di2 rear derailleur review

Clutch mechanism reduces unwanted chain movement and quiets drivetrain

Parts
Shimano Ultegra RX Di2 Rear Derailleur Review

Outside of a small weight penalty, there really is no downside to the Shimano Ultegra RX rear derailleur. Photo courtesy Shimano/Eric Wynn

What is it

Taking a page from the mountain bike arena, but with a few drop bar tweaks, Shimano’s Ultegra RX rear derailleur utilizes the company’s Shadow Plus clutch mechanism to reduce unwanted chain movement — and quiet down the drivetrain on rough terrain. It’s available in mechanical and Di2 versions, and adds about 70 grams over the equivalent standard Ultegra version.

Shimano Ultegra RX Di2 Rear Derailleur Review

To test Ultegra RX, we rode this Di2-equipped Allied Alfa All-Road adventure bike at the Almanzo 100 in southern Minnesota.

Like Shimano’s mountain bike derailleurs, Ultegra RX has an on/off switch located next to the upper pulley, meaning you can turn off the clutch when riding on smooth pavement. (SRAM has a similar system for dropbar bikes, but it’s only available for 1x systems and does not have on/off functionality.)

Ultegra RX is compatible with all Shimano 11-speed road groups, works with cassettes ranging from 11-28t to 11-34t, and has a max chainring capacity of 16t, meaning it plays nice with all the standard offerings, including 48/32, 50/34, 52/36, and 53/39. Press play to learn more.

Pros
  • Eliminates unwanted chain movement
  • Reduces drivetrain noise on rough terrain
  • Easy to turn clutch on or off
  • No more chipped chainstays
  • Available in mechanical and Di2 versions
  • Flawless shifting performance
  • Compatible with 1x and 2x drivetrains
  • Compatible with all dual-control Shimano shift levers
Cons
  • Minimal loss of drivetrain efficiency
  • Slightly more wrist energy required to shift mechanical system
  • Small price increase versus standard Ultegra rear derailleur
  • Small weight penalty
Shimano Ultegra RX Di2 Rear Derailleur Review

RBR features editor Jason Sumner emerges from a cloud of dust while testing the Ultegra RX rear derailleur at the Almanzo 100. Photo courtesy Shimano/Eric Wynn

RoadBikeReview’s Take

Racing often comes down to the mental game. Whichever riders can keep their mind in a positive space will often have the most success. That’s especially true with long distance events such as the ever-growing number of gravel road racers that are popping up all over the U.S.

This growth in road-less-traveled racing and riding was among the primary drivers behind Shimano’s Ultegra RX clutch equipped rear derailleur, whose main function is to control (and quiet) your drivetrain. Because even if everything is otherwise working perfectly, just the sound of your chain slapping around can mess with your mind.

Shimano Ultegra RX Di2 Rear Derailleur Review

The calm before the storm at the Almanzo 100, which starts in tiny Spring Valley, MN. Photo courtesy Shimano/Eric Wynn

“During the research phase of the [Ultegra RX] project we went to some of these gravel races and talked to the people riding in them,” explained Dave Lawrence, road product manager for Shimano North America. “What we often heard is that in these extreme endurance events, mental attitude is huge and if you can reduce stress it makes it easier to finish the ride.”

Flash forward to mid-May of this year, and I got the chance to ramble around the quiet countryside in southern Minnesota, home to the annual Almanzo 100 gravel road race that starts and finishes in tiny Spring Valley. The objective, besides having a little fun and hopefully getting to that finish line, was to get some firsthand experience on the Shimano Ultegra RX rear derailleur.

Shimano Ultegra RX Di2 Rear Derailleur Review

Registration for the Almanzo 100 is as simple as sending a postcard outlining your intent to show up. There is no registration fee.

Prior to race day, myself and a handful of other bike journalists did a pair of shakedown rides on our loaner Di2-equipped Allied Alfa All-Road adventure bikes. All told, we got about 140 miles of test time. By the end of the three days, consensus was clear: Ultegra RX does exactly what it is supposed to and does it very well. Shifting is fast, precise, and utterly flawless. Drivetrain noise is utterly undetectable.

Check out the RoadBikeReview review of the Allied Alfa All-Road bike.

My only nagging question at the end of the exercise is why would you ever turn the clutch off? Shimano’s Lawrence offers that there may be a small hint of lost efficiency and a tad more required wrist energy for shifting mechanical set-ups (which we didn’t test). But mostly he just shrugged his shoulders, offering that is also makes removing the rear wheel a little easier.

Shimano Ultegra RX Di2 Rear Derailleur Review

When the switch is on, chain retention is improved and noise is all but eliminated.

Shimano Ultegra RX Di2 Rear Derailleur Review

Flip the switch to off for easier rear wheel removal or when riding only on paved roads.

Indeed, while all that might be true, having the clutch engaged (which tightens a friction band around the derailleur’s main pivot) undoubtedly improves shifting because your chain and derailleur cage aren’t jumping around when you’re trying to shift gears. And that increase in efficiency likely offsets any minimal power loss. Combine that with the added peace of mind and Shimano has a clear winner on its hands.

Shimano Ultegra RX Di2 Rear Derailleur Review

Chain retention and the peace of mind that comes with it were the primary drivers in bringing Ultegra RX to market. Photo courtesy Shimano/Eric Wynn

Rating: 5 out of 5 5 stars
Price: $110 RX mechanical, $285 RX Di2 (tested)
More Info: bike.shimano.com

About the author: Jason Sumner

An avid cyclist, Jason Sumner has been writing about two-wheeled pursuits of all kinds since 1999. He’s covered the Tour de France, the Olympic Games, and dozens of other international cycling events. He also likes to throw himself into the fray, penning first-person accounts of cycling adventures all over the globe. Sumner, who joined the RoadBikeReview.com / Mtbr.com staff in 2013, has also done extensive gear testing and is the author of the cycling guide book "75 Classic Rides: Colorado." When not writing or riding, the native Coloradoan can be found enjoying time with his wife Lisa and daughter Cora.


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