tl;dr it’s plastic

In 1962 Simplex introduced the Simplex Prestige, state-of-the-art and one of the most technologically advanced derailers of the time with dual sprung pivots (the pivot at the hanger is sprung in addition to the cage being sprung), one of the most prolific derailers of the bike-boom era. Using brand new state-of-the-art synthetic materials, it was significantly lighter than its steel predecessor, the Juy 61. That state-of-the-art material was Delrin, a plastic.

Five years later, Shimano introduced the Sky Lark, their first dual-sprung derailer, with what Shimano would dub their ‘servo-pantograph’ technology, but in fact a copy of the Simplex design. Unlike the Simplex Prestige however, the Shimano opted for heavier chromed steel of the discontinued Juy 61. This would become the quintessential Shimano derailer, with many variants, and manufactured continuously in one form or another to the present day. The modern derivative is still in production under the Shimano Tourney label and it is the design the SunRace M2T and many others are based on.

Skip forward about a quarter century to 1984, and SunTour’s patent on the slant parallelogram expired. While both ‘servo-pantograph’ dual sprung pivots and slant parallelograms attempt to follow the cassette, the slant parallelogram does a better job most of the time. SunTour had tried to create an indexed system with their Mighty Click, but it did not catch on, being poorly marketed and rather niche since it was neither especially affordable nor top of the line.

After a few abortive attempts at indexing (such as Positron), Shimano, ever the innovators, introduced Shimano Indexing System (SIS) combining SunTour’s slant parallelogram with Simplex’s dual-sprung pivots (and hanger compatibility from Campagnolo). It was a success in no small part due to marketing, and being paired with Uniglide shifting aids. A couple years later, SIS was introduced for 600 (the predecessor to Ultegra) and 105.

From here on, 105 gained its reputation as an affordable and up-to-date group set that was the ideal compromise between price and performance, function, reliability and durability. New releases of 105 were technologically similar to contemporary Dura-Ace, just a bit heavier and less polished. Dura-Ace would be a test bed for new standards and technology which didn’t always pan out. Ultegra was less experimental and exotic but still commanded a premium. 105’s affordability without loss of functionality meant that 105 would go on to be Shimano’s best selling group set.

Unlike Dura-Ace and 600 which used aluminum construction for the most part, 105 retained not just the dual-sprung pivots from its Skylark heritage, but also some of the steel construction. 105’s name and lineage come from the pre-SIS non-slant Golden Arrow series which used 105 in the part numbers and shared similar construction using a mix of aluminum and steel. The aluminum parts were on the outside to give a premium appearance, the cost saving steel parts were hidden away out of sight. Shimano officially considers Golden Arrow a 105 series group set, however Golden Arrow is really only 105 in the sense 600 Arabesque is Ultegra.

The first generation SIS 105 rear derailer, RD-1050 (6-speed), had aluminum knuckles and outer link, but the inner link and pulley cage were chromed steel, linking the material construction to the Skylark unlike the higher-end all aluminum designs. This design would see slight modifications up through 105SC’s RD-1056 (8-speed) which, thanks to Shimano’s new Hyperglide shifting aids which are still used today, featured Shimano Total Integration (STI) alongside downtube shifters.

The Shimano 9-speed era saw the banishment of downtube shifters from group sets in favor of the total integration of Shimano’s STIs and also a new parts number designation, for 105, 5X00 starting with 5500. RD-5500 used a new return spring configuration, a helical extension spring spanning two of the parallelogram pivots much like on a balanced-arm lamp. Compared to a torsional spring acting at just one pivot, this had the effect of making the return force more constant across the entire cassette. By this point it had lost the steel pulley cage in favor of an upgraded lighter aluminum one, but retained the steel inner link and dual sprung-pivots of its predecessors which would continue for almost two decades.

Shimano 5600 10-speed modifies the front A-knuckle pivot (the one with the pulley cage) so that the outer pivot lugs are on the outer link instead of the knuckle, which marginally stiffens the derailer, but was largely a styling exercise in modernizing the appearance. RD-5700 shared the same architecture, but restyled with bolder, sharper lines. Both retained the steel rear plate and dual sprung-pivots of their predecessors as well.

With 11-speed 5800, the construction remains mostly the same, but the anchor bolt is repositioned to change the actuation ratio, making it less sensitive to cable friction. This change was necessitated by the closely spaced 11 speed cassette and the relatively poor shifting reliability of 5700 which introduced higher friction under-the-tape shift cable routing to 105. The spring is slightly modified, attaching to pins in the plates instead of using the pivots and the inner link is painted black instead of chromed. It also retained the steel inner link and dual sprung-pivots of its predecessors.

Now, half a century after Shimano’s Skylark, all traces of it are gone from 105. Shimano R7000 comes with a radically different design dubbed ‘Shadow’ borrowed from their MTB designs. Shimano has shed the ‘servo-pantograph’ design taken from Simplex in favor of the single-sprung ‘Shadow’ design in some ways reminiscent of the single-sprung slant-parallelogram Sun Tour designs. While the new for road ‘shadow’ design received much fanfare in various press releases, the changes in materials went without mention.

Not to be confused with Shadow+, Shimano’s current CX and MTB clutched derailers, Shadow was a radical redesign of Shimano’s MTB derailers that was introduced a decade ago. It represents a major purge of Shimano’s herritage of Shimano’s derailer design.

Gone are the dual sprung pivots copied from Simplex. After squeezing Suntour out of the market about a decade earlier, Shimano copied the single-sprung slant-parallelogram designs of SunTour and the concentric jockey of their GT derailers (something SRAM has also done).

If SunTour was bold enough, they likely would have done what Shimano did and introduced their own ‘direct-mount’ hanger standard optimized for a slant parallelogram instead of using Campagnolo’s hanger standard that dates back to its single-sprung and non-slant designs. Usurping Campagnolo was something Shimano yearned to do back in the days of downtube shifters when Shimano created their own downtube shifter boss which never caught on. Although a ‘direct-mount’ to Campagnolo adapter comes standard with every shadow derailer, even Campagnolo has acknowledge Shimano’s standard and uses it for their new 12-speed group.

Shimano did not stop there and innovated a new cable geometry to shorten the rear housing and reduce the profile of the derailer, shielding it from damage.

It’s not just the design that is different. While the SLX is similar in construction to its predecessors, the materials for 105 R7000 are different. Ultegra had an alloy inner link for generations, but in recent years, carbon fiber has been finding its way into Dura-Ace and Ultegra. Prior to R7000, every 105 rear derailer had a steel rear inner link, linking 105 to Shimano’s early Skylark derailers. However, in its place is a newer, lighter and radically redesigned cast linkage. Where Shimano once copied Simplex design, but deviated in materials, Shimano now does the opposite. Shimano now copies the materials of Simplex, even though it abandoned the Simplex dual-sprung design. In other words, 105 is now being made from plastic.

Many attribute the poor reputation, poor durability, poor performance of the Simplex Prestige due to the fact it was made out of plastic, as well as the tendency to break and get tangled in the spokes. That’s the direction 105 is heading with R7000. It’s not all plastic, but neither were later models of Simplex. 105 has long held a reputation of being the durable no-nonsense Shimano groupset, considered by some to be the minimum serious groupset. The one where Shimano wouldn’t cut corners or use inferior materials at the expense of functionality. Plastic in the rear derailers was relegated to low end ‘garbage’ like Sora and Tourney, or found in off-brands like SRAM, Microshift, the infamous Campagnolo Xenon, or the even more infamous Simplex Prestige.

Of course there is some plastic in virtually all derailers. Jockey wheels, barrel adjuster indexers, locking inserts for adjustment screws are usually made from plastic, but those are not primary structural components. Other components like pedals and shift levers make copious use of structural plastic, although it is not unknown for the plastic to crack or wear excessively. Shimano cassettes with reinforced plastic spiders are notorious for breaking under load.

What truly betrays the usage of plastic here, where even Tiagra, Sora and Tourney derailers use steel and aluminum, is the pivot pins. Interestingly the RD-R7000 introduces a new kind of pivot in the outer A pivot which consists of a steel pin that rotates with the inner lug of the A knuckle, but examination also shows a riveted pin. On their high end models, Shimano press-fits the pivot pins into aluminum, often with a telltale cross mark at the holes. When it comes to plastic or steel knuckles, they use a different kind of pivot, one with a head that flares like a rivet.

The Sora RD-3400 is an excellent example of this. So is the Tourney RD-TX75 which has an alloy front linkage. It becomes immediately obvious about the design philosophy of where the two different kinds of pivots are used. For any given pivot, if the outer lugs are alloy, it gets the press-fit pin. If the outer lugs are plastic or steel, they get the rivet-style pin with a flared head and dimpled end. This makes is obvious that the cast inner link of R7000 isn’t aluminum, it’s plastic. The inner link has the outer lugs where it mates to the A-knuckle. It also uses the flared rivet used for plastic.

At first glance, it seems like the lower A-knuckle is made from aluminum since stock photos of the silver R7000 show a bright aluminum finish. However, it wouldn’t be the first time plastic has been used for an A-knucle. SRAM does it, so does Microshift. Shimano does it on Sora and lower too and all but one of the derailers pictured above. It wouldn’t be the first time Shimano painted a plastic A-knucle silver either. Sora RD-3400 is an example for which Shimano has done exactly that.

Initially the new inner link might be assumed to be a cast aluminum upgrade to replace the heavy and pedestrian stamped steel plate in prior 105 derailers. However, it is telling that it is black on both the black and silver versions and the pivot pins reveal its true nature. Its also very different from the stamped steel inner link on a SLX (105 MTB equivalent) ‘Shadow’ derailer. Clearly the switch from steel to plastic for the inner link is not because it is needed due to the complexity of the new design. If there is any consolation, it is that plastic doesn’t rust.

R7000 wouldn’t be the first Shimano derailer to use a plastic link either. Alivio RD-M4000 is described as having a “resin plate body and carbon fiber reinforced plastic outer link for reduced weight,” the plate body meaning the knuckle. However, oddly enough, Alivio uses a steel inner link.

Previously there had been a logic to the Shimano hierarchy, where as you went up, bits of plastic and steel would be replaced by aluminum, and in recent years, aluminum replaced by the occasional carbon fiber. All that has gone out the window. The old SLX RD-662 had an aluminum A-knuckle, so clearly it isn’t that Shimano couldn’t have made it out of aluminum. Even if the inner link being made from plastic instead of steel is a sidegrade, the A-knuckle being made from plastic instead of aluminum is a clear downgrade by Shimano’s old standards. The direct-mount pivot bolt is also noticeably sloppier on 105 RD-R7000 than SLX RD-662, making the new 105 R7000 feel noticeably cheaper than the decade old SLX RD-662.

Previously I had speculated based on stock photos, but $40 later and I had a 105 RD-R7000 to confirm my suspicions. Limited destructive testing was performed by taking a soldering iron and seeing if the parts would melt, since a soldering iron can’t melt steel links or aluminum knuckles.

Doing some additional digging after wasting money on this, buried away on the Shimano website is a tech doc with technical specifications. It turns out this cost-cutting isn’t unique to 105. Previous generation Ultegra RD-6800 used CFRP A-knuckles. Current generation Ultegra RD-R8000 uses GFRP (p. 156).

It’s a subtle change. Both the letters C and G derive from the same letter and are related to K, in Japanese the ‘G’ characters are modified ‘K’ characters. Unless you pay attention, you might not notice the serif on the ‘G’. CFRP stands for ‘Carbon Fiber Reinforced Polymer’ commonly known as carbon fiber. While I suppose technically CFRP could stand for injection molded plastics with short strand carbon fiber filler, it doesn’t seem to be used for that often. GFRP on the other hand stands for ‘Glass Fiber Reinforced Plastic’ which includes fiberglass, but is also commonly used to describe injection molded plastics mixed with short strands of glass fibers a fraction of a millimeter long, which is certainly what this seems to be.

Ultegra RD-R8000 also uses GFRP for the inner link like 105. Like previous generation Ultegra and Dura-Ace, Dura-Ace RD-R9100 still uses aluminum, so using plastic here is clearly a cost cutting measure. For Ultegra’s and Dura-Ace’s entire history, the inner link has been aluminum (count yourself lucky that I don’t keep a collection of Dura-Ace and Ultegra on hand). While that continues for Dura-Ace R9100, it ends with Ultegra R8000.

On 105 RD-R7000, the A-knucle (plate body) did not seem to be made of the same kind of plastic as the inner link, but according to Shimano, GFRP is used in the inner link and A-knuckle for both Ultegra R8000 and 105 R7000.

Is it to save weight? The sales blurb for Alivio seems to imply so, and R7000 is certainly lighter than the previous iteration of 105 or the SLX. However compared to RD-5800, it only saves about 10 grams or so. The savings is greater compared to the SLX, but part of that is the longer cage and the MTB derailer being overbuilt for ruggedness. Lighter weight in cycling always makes for better press, although any mention of the usage of plastic to reduce weight is notably absent from all R7000 press releases. R8000 too for that matter.

Is it to cut costs? The sloppy direct-mount pivot bolt and the plastic A-knuckle on the 105 RD-R7000 compared to the aluminum one on the SLX RD-M662 seem to imply so. The single sprung design is also likely easier to manufacture. Quality chrome seems to get more expensive by the year as we now understand the true costs of toxic chemicals used in their manufacture and no longer just dump them in the nearest river. Previous generation 105 RD-5800 got rid of the chroming process in favor of paint, and R7000 gets rid of the steel inner link entirely. RD-R8000 was downgraded to plastic from aluminum, even when RD-R9100 uses aluminum. My guess is yes.

Does it matter? Newer clutch designs also seem to use plastic for the A-knuckle as well, but that it likely due to the complexity of the casting. Traditionally, Shimano used more plastic and steel on lower end models, and aluminum on higher end models. While Sora is very usable, if you were the type snub Sora for cheapness, or Tourney for use of plastic, I see little reason why 105 should be different. These and other derailers work fine for the most part, but it does make it feel cheaper, and it’s hard to say making things from plastic exudes a sense of quality or durability. People have been using R7000 and R8000 ignorant of the fact but haven’t seemed to notice yet.

This isn’t something reported by cycling journalists paid to republish official press releases. I certainly haven’t found anyone else mention this before. Plastic in a 105 rear derailer? Combine that with the new R7000 bonded cranksets that glue a sheet-metal stamping to a non-hollow forging, a manufacturing method which has seen many failures at the premium Ultegra and Dura-Ace level. The new cranks don’t even use the same chainrings as the old ones, meaning chainrings are only compatible for one generation. Neither the derailer nor the crank inspires confidence in the new and hyped 105 R7000. The one thing good about R7000 is the new hydraulic STIs which replace the monstrous non-series ones. R7000 gets two thumbs down, one for the derailer and one for the crank.

If you found this post interesting or helpful, please consider buying this piece of fantastic plastic I do not particularly want or need from me for $40. Alternatively consider using my eBates referral link to save yourself $10 and help me pay it off then buy replacements for the 5800 I sold in anticipation of R7000.

The old version of the post can be found here.