Comments on: Accurately Measuring Cable Pull

By: tassos

tassos — Thu, 13 Jun 2013 10:48:22 +0000

Hi if i get it , you convert a bar end shifter to work with a geard hub correct ?
Is possible to make a shimano SIS to work correct with a nexus 7 speed hub , so i can put a downtube shifter ?

By: Alex Wetmore

Alex Wetmore — Sun, 05 Jun 2011 18:23:34 +0000

I don”t have any non-Shimano shifters around. I”ll send you an email offline about this though, I think I can help you out.

By: John Allen

John Allen — Sun, 05 Jun 2011 15:32:30 +0000

Alex — have you measured cable pull for any other compnents? I have read Chris Juden’’s article on the CTC (UK) site about Shimano/Campagnolo rear-derailer compatibility, used his measurements (though I suspect their accuracy — they are rounded to the nearest 0.1 mm per click). I have done some measurements myself, though not with as fine a tool as you have made; I have been in correspondence with JTek and obtained some data there. My goal is to assemble a comprehensive workbook listing the possible compatibilities and put it on sheldonbrown.com. I already have created most of the workbook, but fine-tuning measurements would be helpful. Any measurements you can contribute would be most appreciated and will be credited.

Linear travel agents! I made one some 30 years ago to trim the front derailer when shifting the rear derailer. It was crude but it worked.

I”d be wary of using a pulley as small as 8.9 mm — fatigue failure of cables already is a problem with the typically 16 mm or larger pulleys used for shifters.

By: AlexWetmore

AlexWetmore — Sun, 26 Oct 2008 20:52:09 +0000

Greg — The Travel Agent is designed for housing on both ends. You might be able to mount it in the final loop of housing that goes to the hub. The other option would be making a housing stop that fits under the bottom bracket (this would be a fairly easy part for me to make).

Justin — It’’s hard for me to tell if their shifter is indexed at all, or just a fancy looking friction shifter. It says one shifter is for the 3, 4, 7, or 8sp Nexus hubs. I doubt that the cable pull is identical for all of them (but maybe I”m wrong).

alex

By: Greg

Greg — Sun, 26 Oct 2008 18:03:20 +0000

I can”t tell from looking, but is it necessary to have a full cable housing run going to and exiting the Travel Agent? It would be nice to be able to mount it under the bb shell getting it out of sight and allowing the use of a downtube shifter if you wanted.

By: Justin Miller

Justin Miller — Sun, 26 Oct 2008 09:01:59 +0000

Alex, if it works it will be a big improvement over the various shifter cludges out there (e.g., hubub’’s and drop bars that come apart). I wonder if the folks at Firebikes did similar research to develop their downtube shifters for Nexus hubs. http://www.prestosell.com/cgi-bin/order.pl?ref=firebikes&fm=1
Justin

By: AlexWetmore

AlexWetmore — Sun, 12 Oct 2008 06:56:29 +0000

Rory — I”m up for measuring any shifters that folks in Seattle want to bring over. It doesn”t take much time and the tool isn”t going anywhere (the scale might go back on my mill, but it’’s easy to reconfigure).

Matt — I think the effective radius is the depth of the root of the pulley plus the radius of the cable. I”ve considered a linear travel agent (like the Sidetrak BPB), but modifying them isn”t that much easier. The pulley’’s aren”t too hard to make on the lathe.

By: Matt Newlin

Matt Newlin — Sat, 11 Oct 2008 00:34:09 +0000

Pretty cool. Have you considered a linear travel agent: a lever in the middle of a long span of cable, like on the down tube? That way, it would be easy to make the ratio adjustable. Just make both cable pivots on the same radial line from the lever pivot. Kinda ugly though.

I suppose you could just turn down one pulley or the other to adjust the ratio too. Do you know the effective radius of the cable on the pulley? I”d guess a little larger than the distance to the center of the cable.

By: Rory

Rory — Fri, 10 Oct 2008 17:24:26 +0000

do you want to measure with a campy-brifter? while I”ll say the benefit being using a modern brifter that also has a brake opening thing, but I”m actually more selfish-ly interested for maybe building up another internal geared bike.

By: AlexWetmore

AlexWetmore — Fri, 10 Oct 2008 13:59:44 +0000

I should take a photo of my first attempt. It was an ugly thing with sliding pieces of brass and a dial indicator. Lots more work, less accurate, and much more of a pain to use.