I LOVE the Shimano Nexus 8 Premium (red band) hub on the bike. Unfortunately, Shimano does not offer a shifter for this hub that fits on road bike handlebars. As a result, I am stuck with mountain bike handlebars. (I actually cornered a Shimano engineer at Interbike to talk with him about this. Another guy was doing the same thing as I walked up to him. So this seems to be something people want.) I go back and forth on whether I actually need a road bar, but I feel it is a technical challenge to figure out a way to adapt another shifter to work with the Nexus (and Alfine eventually). The challenges are:
1) The Nexus requires a cable pull between shifts that is different from any other shifter out there except for the Nexus-specific shifter.
2) Internal hubs need to have the cable very precisely controlled or the mechanisms will wear quickly.
So in order to figure out just how much cable the Nexus shifter pulls I used a Sharpie to put a dot on the exposed part of the cable next to the shifter as a reference. I measured the full travel of the dot from 1st to 8th gear. Here is a table with what I measured:
| inches | mm | actual step mm | |
| 0.124 | 3.1496 | | gear change |
| 0.327 | 8.3058 | 5.1562 | 1-2 |
| 0.528 | 13.4112 | 5.1054 | 2-3 |
| 0.732 | 18.5928 | 5.1816 | 3-4 |
| 0.990 | 25.1460 | 6.5532 | 4-5 |
| 1.149 | 29.1846 | 4.0386 | 5-6 |
| 1.350 | 34.2900 | 5.1054 | 6-7 |
| 1.555 | 39.4970 | 5.2070 | 7-8 |
| | | 5.1925 | avg |
I believe that there is supposed to be uniform spacing between gears, which means that my shifter is not the most precise instrument in the world, at least on its location of 5th gear. I imagine that somewhere at a Shimano plant the plastic castings have the detent hole for 5th gear just slightly off. Or I have a piece of sand in mine. This non-uniform gear spacing might explain the little noises I heard that led me a few months ago to tear down the whole hub in a fit of mechanical paranoia. I did not find the metal shavings I had imagined were in there. It looked beautiful. But that is a post for another time. Based on these measurements, I feel pretty comfortable saying that increments between gears is 5.2 mm. Now we have something to work with.
So, what is the cable pull for shifters out there. Taking information found around the web (specifically this very good article on Shimergo (combination of Shimano and Campagnolo components), I found these cable pull figures:
| | Cable Pull |
| Shifter | (mm) |
| Shimano 6 | 3.2 |
| Shimano 7 | 2.9 |
| Shimano 8 | 2.8 |
| Shimano 9 | 2.5 |
| Shimano 10 | 2.3 |
| Campag 8 | 3.5 |
| Campag old 9 | 3.2 |
| Campag new 9 | 3.0 |
| Campag 10 | 2.8 |
| Sram (1.0) 7 | 4.5 |
| Sram (1.0) 8 | 4.3 |
| Sram (1.0) 9 | 4.0 |
| Shimano Revo Nexus 8 (mine) | 5.2 |
So, what to do?
A really cool place called Jtek engineering makes a device called a ShiftMate, which seems to be a pulley that alters the pull ratios by using two different sized diameters on one pulley wheel. Using the information on Jtek's website about where their product fits, along with information about the sprocket pitches of common sprockets, I think I can calculate the ratio changes that the different ShiftMate wheels are capable of. First, sprocket pitches from around the web:
| Cassette or Freewheel | Sprocket Pitch | Code |
| | (mm) | |
| All modern 5 and 6-speed | 5.5 | S5/6 |
| All standard 7-speed | 5 | S7 |
| Campagnolo 8-speed | 5 | C8 |
| Shimano 8-speed | 4.8 | S8 |
| Campagnolo 9-speed | 4.55 | C9 |
| Shimano 9-speed | 4.35 | S9 |
| Campagnolo 10-speed | 4.15 | C10 |
| Shimano 10-speed | 3.95 | S10 |
And now put it together with the Jtek information in a spreadsheet and solve for the ratios that Jtek must be using. I should point out that this Jtek device is very clever. At first I thought I was making a mistake because the ratios I solved for were either 1+ a little bit or 1- a little bit. But it looks as though you can set up the shifter to pull on the small diameter of the wheel or on the large diameter of the wheel (placing the "output" cable to the derailleur on the pulley diameter that the shifter cable is NOT on). So this makes sense. Each wheel is capable of doing one ratio or the inverse of that ratio. (PLEASE NOTE THAT THESE ARE NOT OFFICIAL FIGURES FROM JTEK. I AM CERTAIN THAT I HAVE SOME ERRORS IN MY CALCULATIONS. YOU SHOULD CONTACT THE COMPANY TO GET THE RIGHT FIGURES) Anyway, here they are. Very cool:
| JTEK Product | | | | | | | | | |
| #1 | shifter | pull mm | der | shift ratio | cass | sprock pitch | calc pitch | pitch diff | implied jtek ratio |
| | S8 | 2.8 | S | 1.7 | C8 | 5.00 | 5.00 | 0 | 1.050 |
| | S9 | 2.5 | S | 1.7 | C9 | 4.55 | 4.55 | 0 | 1.071 |
| | S10 | 2.3 | S | 1.7 | C10 | 4.15 | 4.15 | 0 | 1.061 |
| | C8 | 3.5 | C | 1.4 | S8 | 4.80 | 4.80 | 0 | 0.980 |
| | C9 old | 3.2 | C | 1.4 | S9 | 4.35 | 4.35 | 0 | 0.971 |
| | C10 | 2.8 | C | 1.5 | S10 | 3.95 | 3.95 | 0 | 0.940 |
| | C10 | 2.8 | C | 1.5 | S9 | 4.35 | 4.35 | 0 | 1.036 |
| | | | | | | | | | |
| #2 | S9 | 2.5 | S | 1.7 | S8 | 4.80 | 4.80 | 0 | 1.129 |
| | S9 | 2.5 | C | 1.5 | C10 | 4.15 | 4.15 | 0 | 1.107 |
| | S9 | 2.5 | S | 1.7 | S10 | 3.95 | 3.95 | 0 | 0.929 |
| | S10 | 2.3 | S | 1.7 | S9 | 4.35 | 4.35 | 0 | 1.113 |
| | C9 | 3.0 | S | 1.7 | S8 | 4.80 | 4.80 | 0 | 0.941 |
| | C9 | 3.0 | C | 1.5 | C10 | 4.15 | 4.15 | 0 | 0.922 |
| | C9 | 3.0 | S | 1.7 | S9 | 4.35 | 4.35 | 0 | 0.853 |
| | C10 | 2.8 | C | 1.5 | C9 | 4.55 | 4.55 | 0 | 1.083 |
| | | | | | | | | | |
| #3 | S9 | 2.5 | C | 1.5 | C9 | 4.55 | 4.55 | 0 | 1.213 |
| | S10 | 2.3 | C | 1.5 | C10 | 4.15 | 4.15 | 0 | 1.203 |
| | C9 | 3.0 | S | 1.7 | S9 | 4.35 | 4.35 | 0 | 0.853 |
| | C10 | 2.8 | S | 1.7 | S10 | 3.95 | 3.95 | 0 | 0.830 |
| | | | | | | | | | |
| #4 | S8 | 2.8 | C | 1.4 | C8 | 5.00 | 5.00 | 0 | 1.276 |
| | S9 | 2.5 | C | 1.4 | C9 | 4.55 | 4.55 | 0 | 1.300 |
| | C8 | 3.5 | S | 1.7 | S8 | 4.80 | 4.80 | 0 | 0.807 |
| | C9 | 3.2 | S | 1.7 | S9 | 4.35 | 4.35 | 0 | 0.800 |
So, the question now is what to do with this information. I need at least an 8-, 9-, or 10-speed shifter. If I bounce the Jtek products (including their inverse ratios) against all of the shifters in my table, I find a few possible solutions:
| | | jtek (i is inverted) | |||||||
| | Cable Pull | 1 | 2 | 3 | 4 | 1i | 2i | 3i | 4i |
| Shifter | (mm) | 1.05 | 1.10 | 1.20 | 1.30 | 0.95 | 0.91 | 0.83 | 0.77 |
| Shimano 6 | 3.2 | 3.36 | 3.52 | 3.84 | 4.16 | 3.05 | 2.91 | 2.67 | 2.46 |
| Shimano 7 | 2.9 | 3.05 | 3.19 | 3.48 | 3.77 | 2.76 | 2.64 | 2.42 | 2.23 |
| Shimano 8 | 2.8 | 2.94 | 3.08 | 3.36 | 3.64 | 2.67 | 2.55 | 2.33 | 2.15 |
| Shimano 9 | 2.5 | 2.63 | 2.75 | 3.00 | 3.25 | 2.38 | 2.27 | 2.08 | 1.92 |
| Shimano 10 | 2.3 | 2.42 | 2.53 | 2.76 | 2.99 | 2.19 | 2.09 | 1.92 | 1.77 |
| Campag 8 | 3.5 | 3.68 | 3.85 | 4.20 | 4.55 | 3.33 | 3.18 | 2.92 | 2.69 |
| Campag old 9 | 3.2 | 3.36 | 3.52 | 3.84 | 4.16 | 3.05 | 2.91 | 2.67 | 2.46 |
| Campag new 9 | 3.0 | 3.15 | 3.30 | 3.60 | 3.90 | 2.86 | 2.73 | 2.50 | 2.31 |
| Campag 10 | 2.8 | 2.94 | 3.08 | 3.36 | 3.64 | 2.67 | 2.55 | 2.33 | 2.15 |
| Sram (1.0) 7 | 4.5 | 4.73 | 4.95 | 5.40 | 5.85 | 4.29 | 4.09 | 3.75 | 3.46 |
| Sram (1.0) 8 | 4.3 | 4.52 | 4.73 | 5.16 | 5.59 | 4.10 | 3.91 | 3.58 | 3.31 |
| Sram (1.0) 9 | 4.0 | 4.20 | 4.40 | 4.80 | 5.20 | 3.81 | 3.64 | 3.33 | 3.08 |
In particular, it looks like the Jtek 3 and 4 could make SRAM shifters work. More later.
