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, one of the most prolific derailers of the bike-boom era, and remarkably light at only 152g.
[pictures coming soon, I need to find a Simplex Prestige]
Five years later, Shimano introduced the Sky Lark, their first dual-sprung derailer, what Shimano would dub their “servo-pantograph” technology, but in fact a copy of the Simplex design. Unlike the Simplex Prestige however, the Shimano Sky Lark was a chromed steel affair that weighed more than twice as much. A close relative of this design is actually still in production and is the design the SunRace M2T is based on.
Fast forward half a century, and we have the Shimano R7000 group replacing Shimano 5800 with a radically different design dubbed “Shadow” and an all new lighter weight. Shimano had shed the “servo-pantograph” design taken from Simplex in favor of the single-sprung “Shadow” design. It used to be that Ultegra had an alloy rear linkage. Prior to R7000, every 105 rear derailer had a stamped steel rear linkage, linking 105 to Shimano’s earliest derailers. But both the dual-sprung-pivots and that last piece of stamped steel which hark back to the Sky Lark are now gone. In its place is a newer, lighter and radically redesigned cast linkage.
But where Shimano once copied their design from the Simplex design of old, but deviated in material from the Simplex derailers of old, we now see the opposite trend. Shimano now copies the materials of the Simplex derailers of old, even though it deviates from the Simplex dual-sprung design of old. In other words, 105 is now being made from plastic.
Many attribute the poor reputation, poor durability, poor performance or worn specimens, and the tendency to break and get tangled in the spokes of the Simplex Prestige to the fact that it was made of plastic. That’s the direction 105 is heading with R7000. 105 has long held a reputation of being the durable no-nonsense Shimano groupset, considered by some to be the minimum acceptable groupset where Shimano wouldn’t cut corners or use inferior materials. Plastic in the rear derailers was relegated to low end garbage like Sora and Toruney, or found in off-brands like SRAM or Microshift.
At first glance, it looks like the lower A-knuckle is made from aluminum since R7000 has a bright aluminum finish. On closer inspection, the unpainted black version resembles the plastic knuckles of a tourney derailer with clear and distinct mold seams and flash and has a slightly different sheen from the front linkage. 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. It wouldn’t be the first time Shimano painted a plastic A-knucle silver. I have in my parts bin a Sora RD-3400 for which Shimano has done exactly that.
At first the new rear linkage might be assumed to be a cast aluminum piece to replace the heavy and pedestrian stamped steel linkage in prior 105 derailers. However, it is telling that it is black on both the black and silver versions. It’s also very different from the stamped steel rear linkage on a SLX (105 MTB equivalent) “Shadow” derailer I also have. But what truly betrays the usage of plastic here, where even my Tiagra, Sora and Toruney derailers have steel, is the pivot pins. On their high end models, Shimano press-fits the pivot pins into aluminum, often with a tell-tale 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, they get the rivet-style pin. This makes is obvious that the cast rear link of R7000 isn’t aluminum, it’s plastic. The rear link has the outer lugs where it mates to the A-knuckle. It also uses the flared rivet used for plastic.
This isn’t something likely to be reported by cycling journalists paid to republish press releases. I haven’t touched R7000 or even seen it in person, but from what I’ve seen so far, I’m not impressed. 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. This design has seen many failures at the Ultegra and Dura-Ace level. The only thing remotely good about R7000 is the new hydraulic STIs which replace the monstrous non-series ones. I’m sad I sold my 5800 equipped bike in anticipation of the new 105. Two thumbs down, one for the derailer and one for the crank.
On the off chance I’m totally wrong and there’s some other explanation for the rivet and why everything else seems to fit a plastic rear linkage and A-knuckle, great, I’ll be thrilled that Shimano isn’t trying to cheapen the quality of 105.