Ted:
Very interesting and insightful...I learned a lot from your post! It appears RD
ratio is a critical variable that really deepens the analysis one would have to
do bench top to get a feel for how a certain combo of bits would work in theory
before trying. Personally, I think I'd be more inclined to just install the
bits and see how they work before undergoing that much analysis, but it's
educational to at least better understand how bits function together and the
interplay between different parts of a system.
Thanks for sharing!
Scott in frozen ground Montana
On Tuesday, November 29, 2022 at 07:33:10 AM MST, Ted Durant
<teddur...@gmail.com> wrote:
On Sunday, November 27, 2022 at 8:43:17 PM UTC-6 Scott wrote:
Your research task: find out how much RD moves with each ratchet of your
1975s. Then you'll be able to better assess compatibility with different
cassettes of any maker/speed, as long as you get the respective cog spacing.
I spent an inordinate amount of time on this topic and put together a
spreadsheet (naturally). I found 25 clicks on my SunTour BarCons, and 25mm of
total cable pull, so each click is 1.0mm.
Rear derailer ratio, the amount of horizontal movement per mm of cable
movement, varies pretty widely, from 1.1 (Shimano 11 mtn, SRAM 7-9 Mtn) (I did
this before 12 and 13 speed...) to 1.90 (SunTour).
The SunTour BarCon has a pretty small barrel, and 25mm isn't enough cable pull
for a low-ratio derailer across a large number of cogs. For example, a Shimano
11-speed MTB derailer needs 36mm of cable pull.
If you want to dial it in, a Campy newer 9-speed derailer with a matching
cassette needs 3.03mm of cable pull (3 BarCon clicks) for each cog. Or, combine
a Shimano 10 or 11 speed derailer with a SunTour freewheel and you'll use right
around 2mm (2 clicks) per cog.
There aren't many combo's that line up with even 1 mm clicks.
Ted DurantMilwaukee, WI USA
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