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
http://bikesmithdesign.com