Index mechanism in derailleur vs. shifter

Discussion in 'Cycling Equipment' started by David Mackintos, Apr 22, 2003.

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  1. I've been having a bit of trouble with my first-gen (~1992) Shimano 600 STI rear shifter
    lately (probably either gummed up, or just worn out), which got me thinking about indexed
    shifting in general.

    It seems intuitive that more precise, or less finicky, indexing could be achieved if the ratcheting
    mechanism was built into the rear derailleur rather than the shifters. I haven't thought much about
    how this would be implemented, but was wondering if it had been tried (on a mechanical system). The
    main disadvantages of the current system seem to be the reliance on constant cable tension to
    maintain rear derailleur position, and the effects of cable stretch. I would think both of these
    problems could be avoided if the cable was only required to tell the rear derailleur to drop down a
    cog, or provide the power to rise up a cog.

    -David
     
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  2. Ted Bennett

    Ted Bennett Guest

    This idea certainly has merit, as it would mean that almost any shifter could be used, as long as
    you didn't care if there were gear indicator numbers on the shifter.

    Shimano actually did this with an early attempt at indexing known as Positron. It didn't succeed
    because it was a rather low end product and the required precision wasn't there. Later on, indexing
    was introduced with DuraAce first, so that higher prices could support better tolerances. Later on
    the technology trickled down to the cheaper stuff. It was so successful that Campagnolo, who at
    first poo-pooed it as a silly gimmick, was forced to introduce indexing. I still wish that the
    indexing was at the shifter.

    Rohloff uses hub-based indexing with their Speedhub 14-speeder, which works very well, albeit at a
    steep price.

    The next bit of fragile, expensive and finicky silliness will be systems that are electronically
    controlled. Nothing wrong with easy to use and accurate controls, but some of these will use servo
    motors to accomplish the movement, which is foolishness considering that power is easily available
    by mechanical means, via the chain or shift cable.

    > I've been having a bit of trouble with my first-gen (~1992) Shimano 600 STI rear shifter lately
    > (probably either gummed up, or just worn out), which got me thinking about indexed shifting in
    > general.
    >
    > It seems intuitive that more precise, or less finicky, indexing could be achieved if the
    > ratcheting mechanism was built into the rear derailleur rather than the shifters. I haven't
    > thought much about how this would be implemented, but was wondering if it had been tried (on a
    > mechanical system). The main disadvantages of the current system seem to be the reliance on
    > constant cable tension to maintain rear derailleur position, and the effects of cable stretch. I
    > would think both of these problems could be avoided if the cable was only required to tell the
    > rear derailleur to drop down a cog, or provide the power to rise up a cog.
    >
    > -David

    --
    Ted Bennett Portland OR
     
  3. A Muzi

    A Muzi Guest

    "David Mackintosh" <[email protected]> wrote in message
    news:[email protected]...
    > I've been having a bit of trouble with my first-gen (~1992) Shimano 600
    STI
    > rear shifter lately (probably either gummed up, or just worn out), which
    got
    > me thinking about indexed shifting in general.
    >
    > It seems intuitive that more precise, or less finicky, indexing could be achieved if the
    > ratcheting mechanism was built into the rear derailleur rather than the shifters. I haven't
    > thought much about how this would be implemented, but was wondering if it had been tried (on a
    > mechanical system). The main disadvantages of the current system seem to be the reliance on
    > constant cable tension to maintain rear derailleur position,
    and
    > the effects of cable stretch. I would think both of these problems could
    be
    > avoided if the cable was only required to tell the rear derailleur to drop down a cog, or provide
    > the power to rise up a cog.

    An early index system, Shimano's Positron (1973? 74?), incorporated just that idea. A detent
    (spring-loaded ball bearing) engages holes in a plate on the changer. There was no body return
    spring and so the system used an automotive-style push-pull wire running in regular spiral-wound
    casing. Several cost-cutting features made this particular system unreliable but it has been done
    and the concept does work, just as you suggest.

    --
    Andrew Muzi http://www.yellowjersey.org Open every day since 1 April 1971
     
  4. In article <[email protected]>, Ted Bennett
    <[email protected]> wrote:

    > This idea certainly has merit, as it would mean that almost any shifter could be used, as long as
    > you didn't care if there were gear indicator numbers on the shifter.
    >
    > Shimano actually did this with an early attempt at indexing known as Positron. It didn't succeed
    > because it was a rather low end product and the required precision wasn't there. Later on,
    > indexing was introduced with DuraAce first, so that higher prices could support better tolerances.
    > Later on the technology trickled down to the cheaper stuff. It was so successful that Campagnolo,
    > who at first poo-pooed it as a silly gimmick, was forced to introduce indexing. I still wish that
    > the indexing was at the shifter.
    >
    > Rohloff uses hub-based indexing with their Speedhub 14-speeder, which works very well, albeit at a
    > steep price.
    >
    > The next bit of fragile, expensive and finicky silliness will be systems that are electronically
    > controlled. Nothing wrong with easy to use and accurate controls, but some of these will use servo
    > motors to accomplish the movement, which is foolishness considering that power is easily available
    > by mechanical means, via the chain or shift cable.

    Mektronic used the latter style of power take-off, and it was one of the weaknesses of the system.
    However, the coming systems probably will all use similar power take-off techniques, because the
    UCI seems willing to accept "passive" electronic systems but not ones where the servo directly
    pushes the gear changer. They feel the latter may not meet the letter of the "human-powered" part
    of the bicycle.

    Somehow it all reminds me of an old Tank McNamara cartoon where a cyclist has an enormous
    air-conditioner sitting on their handlebars, and the mad sports scientist is saying "as long as it
    doesn't provide propulsion...".

    --
    Ryan Cousineau, [email protected] http://www.sfu.ca/~rcousine President, Fabrizio Mazzoleni Fan Club
     
  5. Bruce

    Bruce Guest

    Precision isn't all you need. You need to be able to overshift to complete the shift. The chain has
    to move past the resting point before the shift can be completed, and that's hard to achieve with a
    design that has indents at the rear der. Using a cable that easily overshifts and then returns to
    the resting spot in the lever works.

    Shimano had a good design with indents in the rear der, but that was before SunTour's patent on
    slant parralellegram design expired. Shimano quickly brought out index shifting at the lever when
    they could use that geometry.

    -Bruce
     
  6. Matt O'Toole

    Matt O'Toole Guest

    "Ted Bennett" <[email protected]> wrote in message
    news:[email protected]...

    > This idea certainly has merit, as it would mean that
    almost any shifter
    > could be used, as long as you didn't care if there were
    gear indicator
    > numbers on the shifter.

    I don't see how this is such a huge advantage. You'd still need compatibility between derailer and
    cassette/freewheel, so it's not like you'd eliminate compatibility issues. There are plenty of
    shifter options for all systems already.

    > Shimano actually did this with an early attempt at
    indexing known as
    > Positron. It didn't succeed because it was a rather low
    end product and
    > the required precision wasn't there. Later on, indexing
    was introduced
    > with DuraAce first, so that higher prices could support
    better
    > tolerances. Later on the technology trickled down to the
    cheaper stuff.
    > It was so successful that Campagnolo, who at first
    poo-pooed it as a
    > silly gimmick, was forced to introduce indexing. I still
    wish that the
    > indexing was at the shifter.

    Indexing at the derailer is problematic because of the slop in the cable system between your hand
    and the index mechanism. You can try to tighten up tolerances all you want, but it's still not going
    to work well. Add to that the dirty and damage prone position of the derailer, and you have a recipe
    for disaster.

    The way around the cable-slop issue is to increase cable pull like Sram has done with their ESP
    system, but that would wipe out compatibility with legacy shifters, which is what you were trying
    to preserve.

    As stupid as they appear to be sometimes, I'm sure the designers at Shimano and Campy thought a lot
    about this stuff, and there are good reasons why things are they way they are.

    > Rohloff uses hub-based indexing with their Speedhub
    14-speeder, which
    > works very well, albeit at a steep price.
    >
    > The next bit of fragile, expensive and finicky silliness
    will be systems
    > that are electronically controlled. Nothing wrong with
    easy to use and
    > accurate controls, but some of these will use servo motors
    to accomplish
    > the movement,

    Servo motors and electric power are generally very reliable, moreso than purely mechanical systems.
    Electric systems have fewer moving parts, can be self-adjusting for wear, etc. They're also cheaper
    to produce than assemblies of precisely machined mechanical parts. This is why they're increasingly
    common in cars, airplanes, etc.

    An electric system could be programmed with a switch to shift any available freewheel or cassette,
    but people buying electric shift systems would not be cobbling bikes together from garage sale
    parts anyway.

    > which is foolishness considering that power is easily available by mechanical means, via the chain
    > or shift
    cable.

    This is the heart of the issue. Anyone who thinks current (and past) drivetrains don't work well
    enough is on crack. I certainly don't want to have to check my batteries before a ride. Even keeping
    lights charged can be a PITA. Electric shifting would push bikes further into the realm of
    silliness. I hope it never catches on.

    Matt O.
     
  7. Ted Bennett

    Ted Bennett Guest

    TB:
    > > This idea certainly has merit, as it would mean that almost any shifter could be used, as long
    > > as you didn't care if there were gear indicator numbers on the shifter.

    Matt:
    > Indexing at the derailer is problematic because of the slop in the cable system between your hand
    > and the index mechanism. You can try to tighten up tolerances all you want, but it's still not
    > going to work well. Add to that the dirty and damage prone position of the derailer, and you have
    > a recipe for disaster.

    The point I was trying to make is that slop between the hand and the index mechanism doesn't matter.
    And I would counter that no matter where the indexing occurs, derailers are still in a dirty and
    damage prone location. That has not been a problem in my experience, but I don't ride off road much.

    TB:
    > > which is foolishness considering that power is easily available by mechanical means, via the
    > > chain or shift cable.

    Matt:
    > This is the heart of the issue. Anyone who thinks current (and past) drivetrains don't work well
    > enough is on crack. I certainly don't want to have to check my batteries before a ride. Even
    > keeping lights charged can be a PITA. Electric shifting would push bikes further into the realm of
    > silliness. I hope it never catches on.

    Agreed.

    The real advantage to electonic controls would be the possible advent of true sequential shifting,
    mediated by one(or more, in various locations) button for UP and one (or more) for DOWN. That would
    eliminate some of the perceived complexity which is intimidating to neophytes.

    --
    Ted Bennett Portland OR
     
  8. Gary Young

    Gary Young Guest

    "David Mackintosh" <[email protected]> wrote:

    > It seems intuitive that more precise, or less finicky, indexing could be achieved if the
    > ratcheting mechanism was built into the rear derailleur rather than the shifters.

    Take a look at Frank Berto's book The Dancing Chain. I don't have a copy in front of my, but I seem
    to recall he had a picture of a SunTour derailleur that mounted to the chainstay instead of the
    derailleur hanger. The detents were built into a disk inside the derailleur. I think Berto said it
    shifted well, but that no manufacturer would spec it because SunTour (which was in its dying days)
    had failed so often in playing catch-up with Shimano.
     
  9. Matt O'Toole

    Matt O'Toole Guest

    "Gary Young" <[email protected]> wrote in message
    news:[email protected]...

    > Take a look at Frank Berto's book The Dancing Chain. I
    don't have a
    > copy in front of my, but I seem to recall he had a picture
    of a
    > SunTour derailleur that mounted to the chainstay instead
    of the
    > derailleur hanger. The detents were built into a disk
    inside the
    > derailleur. I think Berto said it shifted well, but that
    no
    > manufacturer would spec it because SunTour (which was in
    its dying
    > days) had failed so often in playing catch-up with
    Shimano.

    I think they were called X-1, and they came with some cheap mountain bikes for a year or so. I was
    intrigued by the design, not because of the derailer-based indexing, but because of the
    front-entry cable routing. This eliminated the rear loop of cable, which is the source of 90% of
    shifting problems.

    Matt O.
     
  10. In article <[email protected]>, Ted Bennett
    <[email protected]> wrote:

    > The real advantage to electonic controls would be the possible advent of true sequential shifting,
    > mediated by one(or more, in various locations) button for UP and one (or more) for DOWN. That
    > would eliminate some of the perceived complexity which is intimidating to neophytes.

    Those neophytes are probably best-served by a Nexus 7-speed hub rather than an electronic group.

    I brought up your exact point the last time the question of electronic shifters came up. The one
    snag is that the double-shifts have to be very carefully managed, since the rider might not have any
    notice one is coming up.

    --
    Ryan Cousineau, [email protected] http://www.sfu.ca/~rcousine President, Fabrizio Mazzoleni Fan Club
     
  11. Ryan Cousineau <[email protected]> wrote:
    > Ted Bennett <[email protected]> wrote:
    >>The real advantage to electonic controls would be the possible advent of true sequential shifting,
    >>mediated by one(or more, in various locations) button for UP and one (or more) for DOWN. That
    >>would eliminate some of the perceived complexity which is intimidating to neophytes.
    >Those neophytes are probably best-served by a Nexus 7-speed hub rather than an electronic group.

    Or a Rohloff, if they're feeling flush. :)

    [My mother is very pleased with the SRAM 7-speed I built a wheel around for her, but her previous
    gears were a 5-speed rear derailleur, so that already had the up-down thing.

    As a result of that it strikes me that an 11-34 with a moderately sized single front chainring also
    satisfies this "single changer" requirement.]
    --
    David Damerell <[email protected]> Distortion Field!
     
  12. On Tue, 22 Apr 2003 23:53:35 -0400, David Mackintosh wrote:

    > I've been having a bit of trouble with my first-gen (~1992) Shimano 600 STI rear shifter lately
    > (probably either gummed up, or just worn out), which got me thinking about indexed shifting in
    > general.
    >
    > It seems intuitive that more precise, or less finicky, indexing could be achieved if the
    > ratcheting mechanism was built into the rear derailleur rather than the shifters. I haven't
    > thought much about how this would be implemented, but was wondering if it had been tried (on a
    > mechanical system). The main disadvantages of the current system seem to be the reliance on
    > constant cable tension to maintain rear derailleur position, and the effects of cable stretch. I
    > would think both of these problems could be avoided if the cable was only required to tell the
    > rear derailleur to drop down a cog, or provide the power to rise up a cog.

    If your entire experience is with a 1992 STI setup, you haven't experienced "the current system". My
    initial reaction to your 2nd paragraph was to ask what lack of precision, what finickiness, were you
    talking about. Current indexing systems are in fact robust and precise, and require very little, if
    any attention, to stay that way. Also - modern shift cables really do not stretch to any appreciable
    degree, not anything even remotely like they did back in the 60s.
     
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