Lennard’s deep dive: Rotor Uno hydraulic shifting

Photo: Lennard Zinn |

Has Rotor figured out technology that makes the servo motors and rechargeable batteries on electronic shifting systems obsolete? Rotor settled on hydraulic shifting for its Uno group because patents by the big component makers blocked it at every turn in developing either cable-actuated or electronic shifting. But has its ingenuity in circumventing patents led Rotor to a concept that could end up revolutionizing shifting and eliminating the need for so much battery power and wallet lightening?

The fluid pressure in Rotor’s tiny, 3mm-diameter hydraulic shift hose does not push the derailleur in one direction or another. Rather, the fluid only conducts an on/off signal; the force to do the actual shift comes from a pair of springs on each derailleur. Could the big spring that moves the rear derailleur inward to a larger cog or the front derailleur outward to the big chainring replace an electronic servo motor?

Rotor’s single shift lever works just like a SRAM DoubleTap lever: A long swing of the lever shifts up to a larger chainring or cog; a small click of lever drops down to the inner chainring or to a smaller cog; the brake lever is only a brake lever. However, unlike SRAM’s system, which takes force from the fingers to pull against the derailleur return spring and spool cable inside the lever, the only force required to move Rotor’s lever was apparently built into it to give the user a certain feel. Similar to what the big three component makers have done with electronic shifters, Rotor has moved most of the command system out of the shifters and into the derailleurs.

Rotor claims that all there is between the Uno lever and the derailleur is a signal carried by hydraulic fluid. If that’s so, the force for the shift is provided by the derailleur spring. The signal from the lever tells a pawl to move in or out of a toothed bar that indexes the derailleur’s position and allows the spring to unwind or not. Seems to me, anything could carry this signal. The genius lies in making a derailleur that has all of its shifting power housed inside it without requiring a push or pull from the user or from a servo motor.

Given how quickly and smoothly these derailleurs shift, particularly the front derailleur with Rotor’s oval Q-Rings, Rotor may have come up with something quite ingenious. I gave up on Q-Rings on one of my cyclocross bikes after being unable to get good shifting on them with either Campy EPS or Shimano Di2, and I was impressed at how well the Uno front derailleur shifted on them during a few hilly hours on a test bike.

Photo: Lennard Zinn |
Photo: Lennard Zinn |

Will you have to bleed the shifting?

While bleeding a shifter is probably not something many people are going to sign up for, bleeding may not be necessary over the long haul or even upon initial installation. Rotor makes its Uno components in Spain (in Madrid) and then ships them to Magura, since it is Magura’s MT8 disc brakes or RT8 rim brakes that complete the group. Magura assembles the hoses and bleeds the shift and brake systems. With the internal routing on today’s frames, the rear shift and brake hoses do have to be disconnected, if not also shortened. But anyone familiar with installing Magura brakes knows that if you are careful to not lose fluid when disconnecting, cutting, and reconnecting the hoses, bleeding can be avoided.

The 3mm-thin shift hose can be routed through the tiny frame holes designed for Di2 and EPS wires. Once it is connected and bled, it requires no maintenance, since, unlike a cable, it doesn’t develop more friction over time due to dirt contamination. It consistently delivers repeatable performance that shouldn’t degrade, at least now that Rotor has changed its shifter fluid to automotive anti-freeze.

The column of fluid within those thin hoses is super-thin, like a strand of thread. This makes it susceptible to fluid expansion and contraction with increases and decreases in temperature, and as it is a closed system, there is no reservoir to take up the slack. When riders had problems with Uno derailleurs ceasing to function if the temperature changed dramatically over the course of a ride, Rotor switched from using mineral oil to 30 percent Glycol antifreeze, which has minimal volume change with changes in temperature between 5F and 190F (-15C to +88C).

Photo: Lennard Zinn |
Photo: Lennard Zinn |

Drivetrain details

Indexing steps are pre-set in the Uno rear derailleur (11-speed only); the only adjustment after bolting it on is to set one limit screw. The rear derailleur will upshift only one cog at a time, but it can be set to downshift 1, 2, 3, or 4 cogs at a time. There is a screw with four scribed lines sticking out of the derailleur, and the more you back it out to reveal more lines, the more cogs it will move across in a single downshift sweep.

Rotor’s “return to origin” function is unique to the system and designed to speed wheel changes; you flip a lever on on the rear derailleur to disengage the indexing ratchet bar and drop the chain to the 11T cog. In addition to the large housing at the back holding the big coil spring that powers downshifts, there is a standard return spring between the parallelogram plates. The jockey wheel cage is carbon.

The front derailleur is optimized for oval chainrings, incorporating a tall inner cage plate to push the chain up onto Q-Rings. The flat cage plates look old-school compared to the sculpted cage plates we’re familiar to seeing on modern high-end front derailleurs. Nonetheless, I found it to work quite well on a nice, 70km hilly ride in the gorgeous red rocks country around Sedona, Arizona. I did find that it takes a hard push for front upshifts, so either Rotor set the feel for sending this signal quite hard, or you are indeed helping the front derailleur’s downshift spring with your hand.

It does, however, take two clicks to drop to the inner chainring, so there could be a learning curve. This is due to the trim adjustment that feathers the cage to avoid chain rub in small/small gear combinations. The Uno front derailleur has a trim adjustment over each chainring, for a total of four derailleur positions. To go through all of the gears without noise, you have to use all trim positions on both rings, but they do indeed completely avoid rub in cross gears.

If you are used to SRAM DoubleTap shifting, you will immediately shift Uno levers correctly.

I did not mind how fat the Uno lever body is, but people with small hands mentioned to me their preference for a smaller grip. Rotor plans to come out with a narrower lever body, but keep in mind that it does contain two hydraulic cylinders—one for braking and one for shifting. Furthermore, there is a difference in the lever body depending on if it is for a rim brake or a disc brake, as the rim brake requires a larger master cylinder (explained below).

One thing that we used to live with in decades past was slipping lever hoods. Shimano, Campy, and SRAM all have complicated hoods with myriad internal knobs to snap into holes in the lever body, keeping them in place. Rotor is not there yet, however; the Uno hoods slip around.

Rotor CNC machines its cassettes in three pieces that bolt together; the largest two cogs are a single aluminum piece, the next four smaller cogs are another piece, this time in steel, and the smallest five cogs are also a single steel piece. Only 11-28T is currently available (the whole group is supposed to begin shipping in July, but only for sale in Europe at first), but other sizes are promised. The chain is a KMC X11SL with a master link.

Photo: Lennard Zinn |
Photo: Lennard Zinn |

Oh, and the brakes are hydraulic too

To pull off this group, Rotor needed a strong hydraulic partner independent of brands offering complete groups, so it partnered with Magura to add critical parts to its system. The Uno disc brake is a standard Magura MT8 XC brake with Uno graphics; it is only available with 160mm rotors for now. The rim brake is a Magura RT8, an aero-shaped scissors brake that has been on some aero bikes for years.

Photo: Lennard Zinn |
Photo: Lennard Zinn |

Like any nice hydraulic disc, the MT8 is an open system that adjusts to heat buildup as well as brake-pad wear, moving the pistons further out in their cylinders. It’s a nice, stiff, lightweight brake with good heat-management properties. Rotor claims that Uno is the lightest disc-brake group on market, at 10 grams less than SRAM Red22 HRD and 417 grams less than Dura-Ace Di2 disc. Rotor further claims Uno to be among the lightest groups with rim brakes.

The Uno’s RT8 rim brake is a closed system. To compensate for heat, the lever cylinder diameter is bigger for the rim brake than for the disc brake, this why Rotor has two different lever bodies. A recent addition to the RT8 is a little reservoir in front of the brake to not only act as a quick release and to offer adjustment for brake-pad wear but also to allow the brake to accommodate the wide range of rim widths currently on the market. You turn a knob on top of it to add in or take up more Magura Royal Blood hydraulic oil.

I rode the RT8 brake in Sedona, on Lightweight carbon clinchers. It had SwissStop Black Prince pads on it, and I have to assume that they were a mismatch with the rims, because they had an alarming way of not slowing the wheel down on initial contact with the rim. After this initial feeling of careening along without brakes, they would eventually bite and slow the bike as I wished, but an adjustment to my riding style was required to begin braking sooner than I normally would. I also found the quick-release knob to be hard to get at and turn; it certainly does not have the ease of adjustment and quick release function of the SRAM HRR hydraulic rim brake, which features an elegant quick-release lever and barrel adjuster.

Facing long odds

Rotor is facing long odds for market acceptance for more reasons than just brand recognition. Although bleeding shifter hoses and brake hoses may be straightforward enough, it will scare off many a rider and many a mechanic. Just look at how hard it is for Shimano and SRAM to get Belgian cyclocross teams on hydraulic disc brakes. Even though the brakes are clearly better, albeit with a weight penalty, team mechanics are far more comfortable working on cantilever brakes and are reluctant to change. Also, hydraulic shifting has come and gone at least twice before, and I’ll bet you’ve never seen one out on the road or trail. Back in the early 1990s, I had an aftermarket hydraulic shifting system on my tandem. And five years ago, the Acros A-GE hydraulic shifting system for MTBs with elegant toggling levers made a splash but never gained a foothold. Perhaps it was before its time, as 1X systems could have highlighted its benefits. Since Acros used two hoses to move the derailleur one way or the other, you could have separated them on a one-by system, sending each one to a different shifter for two-hand rear shifting, like SRAM eTap. Furthermore, even though SRAM’s HRR hydraulic rim brakes are stellar (IMHO) and have now been out for three years, I challenge you to find a bike in your community with them. Some of this may have to do with SRAM’s recall, but I’ll bet more of it is due to the fact that it is different and requires hydraulic bleeding instead of cable cutting and tightening.

Rotor felt compelled to develop a group because, though its oval chainrings are popular with individual riders, keeping top pro teams riding on Rotor cranks and Q-Rings runs up against the three big component makers sponsoring those teams. Rotor does not yet have any teams on the Uno group, but it hopes that once it does, consumers will demand Uno just like they demanded Q-Rings after seeing famous riders using them.

Retail price of the entire Uno group, with either brake option, is set at 2,499 Euros, which right now converts to over $2,800. Availability and price for the U.S. market have yet to be announced. An impressive amount of ingenuity has gone into this group, and it offers easy, powerful shifting without cable maintenance or battery charging. For bikes with hydraulic disc brakes, the fact that Uno has hydraulic shifting should add no more assembly time or hassle and may in fact save time.

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