Actuation Ratio
When a mechanical gear shifter is moved by the rider's hand, it will pull a fixed amountpredetermined length of inner gear wideBowden cable through the outer housing. The shifterThe derailleur at the other end will move (actuate) a certain amountdifferent distance, which will be differentis determined by the actuation ratio.
Naturally there are many standards, along with exceptions to standards. InIn brief:
Shimano 6/7/8/9 - Rear shift ratio is 1.7, so for 1 mm of cable, the Rear DeraileurDerailleur (RD) moves left/right by 1.7 mm
Shimano calls this 2:1 ratio for marketing reasons.
All these RDs are compatible, and any 6 to 9 speed RD will work perfectly with eithera 6, 7, 8 or 9 speed shifter assuming it(assuming the RD can physically span the width of the cassette). RegardlessThis is true regardless of whether it’s athe shifter and RD are intended for MTB, or road shifter, or RD. They6 to 9 speed RDs are also compatible with Shimano 10 speed road shifters (except the Tiagra 4700 series, which borrows the 11 speed actuation ratio.)
| Name | Ratio |
|---|---|
| Shimano standard 6/7/8/9 speed and 10 speed Road excluding Tiagra | 1.7x |
| Shimano Dura Ace 6 to 8 speeds (vintage stuff) | 1.9x |
| SRAM 2:1 | 1.7x |
| Campagnolo old | 1.4x |
| Shimano 10 MTB | 1.2x |
| SRAM 1:1 | 1.1x |
| Campagnolo new | 1.5x |
| Shimano 11 road and Tiagra 10 speed 4700 | 1.4x |
| SRAM Exact Actuation | 1.3x |
| Shimano 11 MTB | 1.1x |
| SRAM X-Actuation 11-speeds | 1.12x |
| SRAM X-Actuation 12-speeds | 1.01x |
Note that Shimano Internally Geared Hubs (Nexus and Alfine) do not have equal pull distances, so adjacent clicks are NOT the same length. These shifters are incompatible with derailleur gears, and the IGHs do NOT work with normal shifters.
Further info:
