Re: [CR]Quadruple Chainrings

(Example: Production Builders:Peugeot:PY-10)

Date: Sat, 12 Feb 2005 09:10:29 -0600
To: Jan Heine <heine93@earthlink.net>
From: "Mark Stonich" <mark@bikesmithdesign.com>
Subject: Re: [CR]Quadruple Chainrings
In-Reply-To: <a052106debe33b5525fd0@[68.167.254.37]>
References: <000c01c510c9$294fe560$6601a8c0@Balboa>
cc: classicrendezvous@bikelist.org

At 2/12/2005 05:37 AM -0800, Jan Heine wrote:
>The drawings show cross-over gearing. From memory, it may have been
>50-44-36-26 or something like that.

I remember from a photo in the early '70s that spacing was even, suggesting 26-34-42-50 or 26-36-46-56, probably the former. FD looked like a one-off. Don't know what they did for a BB spindle.
>Also, there was some event where more gears got you extra points. But that
>was in the 1940s, and people stretched the imagination by using triples
>and 6-speed (gasp!) freewheels. These were made by brazing extra cogs onto
>5-speed freewheels.

I made a few early 7 speeds that way.
>Finally, I have heard rumors that some people used 4 chainrings on
>tandems. However, I never have seen a machine with that setup.

I initially set up our tandem with 20-32-44-56. Now that we're old and feeble its 20-28-36-44 (and shifts sooo much better) .

OT, but I sell short cranksets to recumbent owners. I set one guy up with 16-26-36-46. And another, who had a 20" drive wheel, with 24-34-44-54.

If you get the BB length just right (maybe with the help of a freewheel spacer under the fixed cup) most modern front derailleurs will handle 4 rings. It's no big trick to extend the cage for big differences. I set up a Franklin triplet with 20-44-60 for 3 local riders to use in P-B-P. Back in the timeline, a friend had longer parallelogram arms made for a Record FD. To handle chain wrap on these setups I'd add a 2nd idler wheel to titanium Huret DuoPars
>If VBQ had an April 1 issue, I might include a techical article on "double
>half-step" - half-step is nice, but with a granny, you get very large
>steps in the smallest gear. By using four rings, you could use a
>50-47-28-25 or so, and get half-step the second time around!

Have you actually done this? Based on my experience, I don't think you would be able to shift from the 25 to the 28 without first going to the 47 and dropping back down. Not a big deal with even chainring steps and a close ratio FW. But I think it would make 1/2 step impractical. I'm not even sure you would be able to make the 28-25 shift.

If freewheel spacing is such that 50-47 gives you even 1/2 steps, 28-25 would give you a bunch of near duplicates. 28-26 would be closer but still a bit wide.

Mark Stonich;
    Minneapolis "It's going to be almost 50 today!" Minnesota
     http://mnhpva.org
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