Were there ever desmodromic shifting systems? Meaning where one cable pulls the derailleur one way, and another cable pulls it the other way? So no heavy spring in the derailleur itself.

Twist-shifter: www.rohloff.de

(Although this is not a derailleur.)

good question.

and IDK the answer, but one of my motorcycles has something related to things desmodromic on the throttle. at least there are two cables on it that work at counter purpose. but in addition, the common throttle bar on the carburetors is spring loaded. i suspect they, in concert, serve a failsafe function.

Shimano Positron, first version. The Positron II used a solid wire and special housing to give a push-pull action. I think some of the early Cyclo rear derailleurs used an "endless" cable and a spiral drum to move the derailleur cage sideways.

Positron 1 shifters: VeloBase.com - Component: Shimano LB-500, Positron



Positron 1 rear derailleur: VeloBase.com - Component: Shimano DG-100, Positron



And then there was the White Industries LMDS derailleur: White Industries LMDS derailleur (The whole Disraeli Gears site is a gas.)

There's a line in Dean Ing's short story "Big Spring": "Desmodromic valves? Of course! They were designed by Herr Desmond Dromic."

yes, what a delightful write-up on the White Industries LMDS derailleur!

I would suggest that the reference of "no heavy spring in the derailleur itself" is not completely valid when one weighs the second cable, casing and frame clips/guides compared to what a spring weighs.


Not many wrenches or riders have actual experience with the early version of Positron (or Negitron as we called it). I assembled dozens of such equipped bikes when working for JC Penny in the early 1970s and serviced many more over the following 15+ years. The twin cable system was rather bulky, slow to respond and took a concerned hand to properly set up for what ever the best shifting was (with it's design). All the twin cable systems that I saw, IIRC, were using a twist grip control. Much like the common then 3 speed grip control and we did have customers complain of inadvertent shifting. These are but some of the reasons that Shimano moved to a single rod (instead of a cable as a cable doesn't transfer a push well) and lever controls by the mid late 1970s. This second design lasted many years and we still see them come through the shop a couple of times a year. They worked much better what with the indexing aspect in the der. Andy.

Would it be possible to modify a, let's say, Nuovo Record derailleur to be actuated by two cables, while removing its spring? Can you think of how it would be done?

I do have a reason for wondering about this.

Because you're crazy? OK, I'll play along.

The tough part would be adding a second cable stop for the "upshift" cable (the original cable is the "downshift"). There's not a lot of real estate on a NR rear derailleur, but here's how I'd approach it: replace the existing inner plate of the parallelogram with another outer plate so that the cable fixing bolt is on top. Add/weld/glue on an additional cable stop on top of the upper derailleur body. That gives you fittings for two cables, one that shifts inward, the other shifts outward. Run a double-length cable to your shifter and back with a set-screw to hold it in place on the shifter (see the Positron shift lever). It should work. I dunno how well it will work, but it ought to move this way and that.

For bikes, there's almost nothing that hasn't been thought of and tried long ago.

The so called "push pull" throttle cables were required at least for IMPORT on all MC over a certain CC displacement, there often was still a return spring, the 1969 and 1970(called a K0) Honda 750's were prior to the requirement. Some of folks when replacing cables never bothered to replace the return cable....it works fine without it, but there is nothing WRONG with the safety feature.

You Buy Or already Own, a Copy of 'The Data Book' , Jyl? Powell's probably has it on the shelf.

https://www.amazon.com/Years-Bicycle-.../dp/1892495015 Likely shows a Prior set doing just that.

Shimano Positron used a solid wire to push and pull back, But the predominant scheme is Bowden type Cable Pulls , return spring pulls Back .

Wow, never heard of this book. I'm tempted to buy it! The reviews are very mixed, though.

The earliest example I've seen is the 1923 "Cyclo" derailleur:

Is your reason for wanting this so you can show off your vocabulary?

I believe two such beasts still exist. One is the Rohloff Speedhub, though that might not be what you had in mind. The other is found on the custom constructeur bikes of C. S. Hirose of Tokyo. There is an article about him in Bicycle Quarterly, No. 53, describing both front and rear shifters.

BITD cable designs were less well executed then what we have today. It was far more common to have cable friction/binding hinder cable movement. Der return springs tended to be heavier/stronger to over come this. Shift levers were also often more sloppy in their friction pack/lever movements. But since the cogs were farther apart then todays and the chains stiffer side to side all still worked well enough most of the time.

Push/pull cables with no return spring (when properly set up with no slack between the two cables) made for pretty reactive call and response. A nice feature given that the indexing was handled (bad pun) by the shifter end of the system (with the Shimano Positron version 1). (Much like the IHG 3 speeds). Andy.

Sorry, I didn't answer Tom back in April.

I was thinking that if you could modify a Nuovo Record RD and FD to be operated by two cables with no spring in the derailleur, then you could connect those cables to small stepper motors. Concealed under the BB.

Rohloff and the NuVinci Hubs are both Pull-Pull 2 cable shifted ..

There is a Motor to roll the Rohloff shifting cam thru the combination sequence.

Australian company makes them.

May be off target a bit, but what about the concept bike that Colnago did? I haven't found much on it but I do remember seeing something about this being used, about 3/4 down the page:

This is the first product of the Colnago/Ferrari partnership was the Concept bike in 1987. Standout features include the hydraulic brakes and single Ferrari inspired downtube shifter that operated the internal gears located in the chainrings. The trussed chainstay and internal geared “desmodromic” chainrings were pretty advanced at the time. Mr Colnago said that it was Enzo Ferrari who said he should build a carbon tri-spoke wheel.

Road Bike Action | First Look: Colnago Ferrari CF8