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Car stick shifts vs. bike front-derailleur operation

We thankfully have a standard for driving automobiles. We can operate a new or a rental car without reading its owner's manual. Reading the manual is useful for many basic details, but the steering wheel, braking, and, especially, shifting are universal.

When bikes do come with an "owner's manual", the manual is written by lawyers ("do not operate without a helmet") and addresses neither basic maintenance nor even operation. It's necessary to search for the actual documents online. The details of operating front derailleurs in conjunction with rear derailleurs have subtleties that make riding a new bike inherently iterative to avoid all chain-cage rubbing.

2x Front derailleurs and the mysterious third middle position

Many 2x (road bike) front-shifter-and-front-derailleur sets have three settings.

The derailleur-cage-at-its-leftmost setting is used for, vaguely, the 50% of larger-cogs rear-derailleur settings. Those are positions I and III in the illustration (although the large-chainring-largest-cog is unlikely to be usable; the chain will most likely rub on the front derailleur cage).

The derailleur-cage-at-its-rightmost setting is likewise used, again roughly, for the 50% of smaller-cogs rear-derailleur settings. Those are illustrated in II and IV in the figure (the smaller-smallest chainring-to-cog is likewise generally unusable).

Illustration

front derailleur shifting

Question

Is there a standard for knowing whether the middle of the front-derailleur shifter is to be used for II only, for III only, or for both II and III?

In other words, when you start riding an unfamiliar bike, do you have to search for its Operator Manual (online, probably) to learn how to shift properly?

Indexed Shifting

Indexed shifting (which is now so widespread it may have completely pushed friction shifting out of the new-bike market for years) greatly helps with the leftmost and rightmost cage positions. The shifting interface consists of a clean click. Each click lands on a precise setting.

If we access the middle position from the large-chainring, we cleanly drop to an indexed position, but I haven't been able to determine whether accessing the middle position from the small-chainring (pulling the cable more taut and lifting the derailleur cage halfway) will always pull the cage also to an indexed position. Does it?

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    Isn't the standard whether or not the front derailleur is rubbing on the chain? You talk about three settings - based on the context of the question you are talking about a friction shifter. It does not have three settings, it is analog.
    – David D
    Jul 15, 2022 at 21:20
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    @DavidD most modern (SRAM and Shimano) derailleurs have a middle "trim" position.
    – Paul H
    Jul 15, 2022 at 21:27
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    @Swifty more than three would be news to me. Do you have an example in mind?
    – Paul H
    Jul 15, 2022 at 21:37
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    I'm still not clear what the question is. Are you asking if the trim position accessed by shifting to the large chainring and then trimming, the same physical position of the derailleur as the trim position accessed by shifting to the small chainring and then trimming?
    – DavidW
    Jul 15, 2022 at 21:38
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    Maybe this is why 1x is so popular. FD's confuse everyone :P
    – Andy P
    Jul 15, 2022 at 22:02

1 Answer 1

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Many left road shifters, including almost all recent higher end ones, have four positions, i.e. there's a trim stop for both the small and large ring.

There is not, nor in practical terms could there be, a standard for what gear combination requires the use of which shifter stop, because the angle of the chain coming off the chainring is meaningfully dependent on chainstay length.

Bikes with long chainstays (say 440mm or more) allow some greater laziness with the trim stops, and bikes with very short chainstays, particularly less than the common 405mm minimum recommended for road groups, can require one to fidget with the trim stops often. (Many TT/tri bikes break the 405mm rule).

Frame alignment is a factor as well. The industry standard (for better or for worse) is that misalignment up to 3mm in either direction is normal, as measured with a tool like the Park Frame Alignment Gauge. That means a possible variance of 3mm (1.5mm possible in each direction), which is a good chunk of the cog pitch of modern cassettes. So even on two of the same model bike, frame alignment could require a different trim stop used on the same gear combination.

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