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I am an armchair inventor and have been tossing around ideas to improve derailleur gears for many years -as have many others if you do a quick check of google patents. With this idea, I think I have an invention to solve the perennial problem of front derailleur chain rub.
Front derailleurs (from now I’ll call it the FD and RD for rear) suffer from chain rub particularly when you select say small-small gears front and rear or large-large. You can often adjust this out with careful FD setup or for seasoned riders a small movement of the left gear lever is all that is needed.
But if your bike is worn or the rider is not experienced chain rub will often result. As someone who used to rent out bikes, I can attest to the inability of most people to grasp this concept and to just ride anyway with the chain rubbing away – or even not touch the front shifter out of fear of inducing grinding noises or chain derailment. Additionally, manufacturers are forced to make the left shift lever design with complex micro adjustment ability rather than a dumb 1-2 position switch (or 1-2-3 for triples) like the rear shifter.
Of course, electronic shifting solves this as the FD “knows” where the RD is so it can micro adjust on the fly. SRAM’s new yaw movement is also part solution but it is still a dumb solution in that it does not change yaw depending on the RD position. Wouldn’t it be great if even on a cable system the FD would move in response to the rear’s position?
Well, I think it can.
On a bike, move the right shifter through its range and look at the cable as it passes under the bottom bracket (unless you have hidden cables). Notice it moves anywhere between 40-70mm depending on your number or gears and brands. The solution is take a feeder cable off the RD cable to connect a mechanism to move the FD a few mm.
I can see the FD moving in one of 2 ways.
Either move the FD a few extra mm a la electronic shifting or twist it like SRAM’s Yaw.
But with either solution, there are 2 possible methods. The FD cable is under considerable tension (much more than RD) so even pulling the FD cable a small amount using the rear shifter would result in noticeably harder rear shifting.
So to not move the FD while under spring tension, have the FD 4-bar linkage mechanism remain the same and to remain under high spring tension. The FD cage would then be a separate structure to move independently of the 4-bar linkage mechanism. It could then either move an additional few mm or twist a few degrees around a pivot point similar to SRAM’s yaw movement.
Of the 2, I favor a twisting yaw design as designing the FD cage to pivot a few degrees is not difficult and could probably be done using a single stamping on the existing multi-slide press (upon which existing FD cages are made). In fact, the FD cage needs only to bend rather than use a pivot which would make manufacture very simple.
I envision using a cam mechanism to translate the 40-70mm of RD cable pull into a mechanism that twists the FD a few degrees.
This may be difficult to understand without a picture but I have only a few sketches and cut up FD’s to prove it works and have no prototype. I’m not looking to patent this (and now that it is public domain, nobody can) and building a prototype is beyond my situation as I have no tools or space so I am turning it over to the bike community for comments or if anyone want s to build one, I’d love to see if it works.
So, any comments? Will it work?
 

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Interesting line of thought. Harkens back to the golden age of mechanical control.

I would worry that the tension balance of the RD would be compromised, and so you wouldn't get the timely and accurate shifts you expect back there. Might be a way around it in a dedicated system.

I'd look at getting rid of the FD entirely, via something along the lines of split 'walking' front rings.
 

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I appreciate thinking outside the box and American inginuity but I think electronic shifting will already do this and since mechanical seems to be at the beginning of the end I do not see a strong business proposition.
 

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They have invented this already. It is called 1x10. Made by SRAM. Of course setting your gear up correctly will prevent most of this issue. On my 2x10 campy record bike I can shift all but one gear without chain rub. If I try to run the 39x11 I get a small amount. None on the big ring in any gear.
 

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They have invented this already. It is called 1x10. Made by SRAM. Of course setting your gear up correctly will prevent most of this issue. On my 2x10 campy record bike I can shift all but one gear without chain rub. If I try to run the 39x11 I get a small amount. None on the big ring in any gear.
SRAM also fixed this with Yaw on the new Red.

And of course, common sense to not cross chain is another one...
 

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Interesting idea. It seems to rest on the assumption that riders should not be required to trim the front derailleur no matter what, which (especially from the perspective of marketing to beginners) is a valid assumption.

But I wonder if a much-improved trim function wouldn't be the better way to go. If you remember friction front shifting, you should remember how easy it was to nudge the lever just a bit to get rid of chain rub, and how you had an unlimited number of trim positions. With the front shift lever where it is now, trimming would be even easier than it was then. Campagnolo has (or had) those small micro-trim clicks, which sort of points into the direction of my thinking here.

A more fundamental question for another approach: is there really a need for indexed front shifting at all? :)
 

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"Begin the unnecessarily slow-moving dipping mechanism."

Dr. Evil - 1997

Sorry I'm with Pirx on this one. I don't doubt that it could be done with some sort of eccentric that could deflect the FD cable on the down tube but setting it up would probably be harder than it's worth. No doubt an interesting academic exercise that might be fun to demonstrate a proof of concept. Realistically I'd say little commercial potential given electronic shifting will gain more market (like it or not)

Trimming the FD is pretty subconscious to me. Sort of like driving an MT car. You just do it naturally after a while.
 

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Need to invent an chain rub amplifier so it can be easily heard as an indication of a cross-chained condition.
Yes. It could also amplify the squeaky chains nobody seems to hear either. Always puzzled when I see what appear to be experienced roadies go by with loudly chirping chains.
 

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Agree with those who said it's a non existing problem. You can always run Campagnolo front shifters or even friction. Otherwise, just adjust the front derailleur for a little bit more or less throw to keep it clear.
 

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Shimano solved the problem a few years ago now, it's called Di2 :)
That's nice. What's even better is that this problem doesn't exist on my mechanical 11-speed Campy group: I can fully cross-chain either way without even noticing it, no trim required. Of course, that doesn't mean I should do that, but it has happened to me on some more leisurely group rides while chatting away with friends, that I suddenly "ran out of gears", realizing that I wasn't in the ring I thought I was. My drivetrain gave no indication that would have alerted me to the fact that I was fully cross-chained.
 

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Agree with those who said it's a non existing problem.
Me too. I can get all of my 10 gears without chain rub and without touching the front der trim adjustment in either ring. Of course proper front der adjustment and sensible length chainstays is the solution here.

But I also agree with Wim's first post. Do we really need front indexed shifting? I'd be happy with the way front shifting used to be with downtube shifters - infinitely variable. It was sooo easy to get the cage just where it was needed.
 

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I don't have FD chain rub on my:
Campy 80's NR/SR (friction)
Campy 11sp Record/Chorus (even in the gears that I don't cross)
Non issue to me.
 
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