Old 12-12-15, 12:02 AM
  #18  
Andy_K 
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I was poking around Google, and I stumbled across this article from Park Tool:

Travel Agent? Installation and Adjustment - Park Tool

The article points to an obvious simplification of the problem: measure the distance from the pivot point to the cable anchor (more or less) and you can calculate the cable pull from that. The 5700/6700 levers complicated things a bit in the the cable rests on part of the lever behind where it is anchored, so I had to measure to the point where the cable is free to move independent of the lever body.

Anyway, after measuring the radius of the virtual circle about which the fixed cable point pivots, you can calculate the amount of cable pulled in a 20 degree swing of the lever (for instance) by the formula:

C = 2 * ∏ * r * 20 / 360

or, if you're a math geek and see that the cable pulled will actually be a chord and not an arc:

C = 2 * r * sin(20/2)

which works out to be pretty close to the same thing.

From there, the kind of cable pull versus lever travel I was trying to measure before is mostly a function of lever shape and where you squeeze it.

So, grabbing my trusty digital caliper and returning to the garage, I found the following:


(Model
  • Pivot radius
  • 20 degree pull)
Gevenalle CXV0
  • 32.5
  • 11.3
Gevenalle CX2
  • 20
  • 6.9
6700-series Ultegra
  • 23
  • 8.0
5700-series 105
  • 23
  • 8.0
4600-series Tiagra
  • 23
  • 8.0
Non-group R700
  • 22
  • 7.6
Shimano 5600
  • 19
  • 6.6
Shimano 6501
  • 18
  • 6.3
SRAM S500
  • 22
  • 7.6
Avid SpeedDial
  • 27
  • 9.4
Avid SpeedDial
  • 33
  • 11.5
Shimano R550
  • 20.5
  • 7.1
Alivio MC11
  • 22
  • 7.6
I have a lot more confidence in these measurements than I did in my earlier ones. Most of this seems consistent with my table above, with a few notable exceptions.

1. My earlier Speed Dial measurements appear to have been way off (as was suggested previously).

2. The SRAM levers seem to be closer to the "New Super SLR" pull that to the old "Super SLR". My earlier SRAM measurements were probably bad too.

3. Despite my absolute certainty to the contrary, the R700 levers do not have the same cable pull as the 5600. This shocked me because they look identical holding them side by side. I measured both of them half a dozen times trying to find an error, but it seems to be what I've got here. Still not convinced, I dug up an old Shimano specification chart, and sure enough the R700 are listed as not "Super SLR". It's like the Michelson-Morley experiment all over again.

I also added a Shimano R550 lever (short pull, flat bar) and an old (pre-V-brake) Alivio MC11.
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Last edited by Andy_K; 02-06-17 at 07:04 PM. Reason: Converted table data to list format
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