Re: [CR]DeMultiplicators and DuoPars.

Date: Sat, 30 Jun 2007 22:51:11 -0500
To: Classic Rendezvous <classicrendezvous@bikelist.org>
From: "Mark Stonich" <bikesmith@earthlink.net>
Subject: Re: [CR]DeMultiplicators and DuoPars.
In-Reply-To: <468645DF.4040404@verizon.net>
References: <468645DF.4040404@verizon.net>

At 6/30/2007 08:00 AM -0400, Harvey Sachs wrote:
>Randy Dugan responded to Charles Andrews:
>
>Not to hijack your shout-out to Charles, but I have an Eco-Duopar
>and a 14-34 Ultra 7, running 46/34 up front with a cheap KMS chain
>on a 1980 Schwinn Voyageur 11.8 city bike conversion. Works great
>range-wise, but it can be tough to shift just one cog at a
>time. This might have to do with the Sun tour ratchet stem
>shifters, which have a large drum. Haven't tried with any other shifters.
>+++++++++++++++++++++++++++++++++++++
>
>Simplex "DeMultiplicators" are available from lots of folks, and
>help solve this problem. Basically, it is a lever that installs on
>the down-tube, and roughly doubles the amount of lever travel
>required for a given movement of the rear derailleur. I'm using one
>with a "Crane" RD and Shimano bar-ends, and it does help "unstack"
>the shift positions.

Actually the ratio change is much less, 21mm :16mm or 1.3125 : 1. http://bikesmithdesign.com/fittings/demultiplicator.JPG However that is enough. Increasing the amount of lever travel for these narrow cog shifts is important. But I think they main reason they help is that due to the higher cable tension required by the DuoPar, you had to set the friction too high on your SunTour ratchet shifters. Then they moved in jerks instead of smoothly. Demultiplicators allowed you to reduce the friction setting to about what was needed for SunTour's mechs. and they were smooth as butter.
> You may have a bit of trouble fitting the cable that runs from the
> demultiplicator to the RD, it is a very small barrel head (as I recall it).

Very small indeed. I used to make cables by adding a small globe of silver brazing filler to the end. If you hang a piece of cable with the end down and add silver, capillary action and surface tension will give you a ball that for some reason will not go below the end of the cable. (At least not up to a 1/4" diameter ball.)

In addition to the cable hassle, the demultiplicator pivots were prone to seizing up if used in salty, wet conditions. (ie. winter in Minnesota.)

A couple of ways to achieve the same result, without the funny 2nd cable. 1. A differential pulley, with a bronze bushing, giving the same effect. http://bikesmithdesign.com/fittings/diff-pulley.jpg

2. Changing the leverage ratio at the derailleur itself. This has the advantage of reducing cable tension in the loop behind the derailleur. http://bikesmithdesign.com/fittings/DuoParMods.jpg I sold quite a few of these fittings to local BarCon/DuoPar users. Too bad there wasn't an Internet back then.

Mark Stonich;
     BikeSmith Design & Fabrication
       5349 Elliot Ave S. - Minneapolis. MN 55417
            Ph. (612) 824-2372 http://bikesmithdesign.com
                        http://mnhpva.org