Parashift: cable travel adapter for mixed shifting

Ratio-changing pulleys are a wonderful hack for bikes. For non-electronic drivetrains, they allow bending the rules normally requiring a stringent pairing of shifter, derailleur and cassette families. Also called travel agents or cable-travel adapters, they are already sold in sturdy CNC versions for specific many use cases: Problem Solvers Travel Agent for helping a regular brake lever to operate a V-brake, or Jtek Shiftmates and WolfTooth Tanpan for shifting mixes. The latter once proposed custom pulley ratios for specific cases, but has since stopped custom orders. This project aims at documenting and allowing custom pulleys, as well as testing waters before ordering a CNC one (though they are plenty sturdy in plastic!).

Compatibility

The original model doesn’t provide guidance regarding which pulley sizes to parameter the model with, and is incompatible with some of them. We made investigation and calculations to provide the ready-made adapters below.

ParaShift groups situations by pulley ratio (between the small and large pulley) in this table. Shiftmate correspondence is only infered and should be crossed-checked with the RD Ratios sheet.

You can find which ratio your shifter/derailleur/cassette mix needs by using the table summarized below:

How it works

Cable-travel adapters use a double, side-by-side (duplex) pulley with grooves at two different diameters, to increase or decrease cable travel. The cable enters on a pulley at one diameter, and exits in a pulley at another. An adapter can be installed either to increase or to decrease cable travel, or it can be used without changing the ratio to take a cable around a corner. The main uses of cable-travel adapters are to make direct-pull cantilever brakes compatible with brake levers for other types of brakes, and to achieve compatibility with mismatched shifter-derailer-cassette combinations.

Focusing on duplex pulleys for shifting, the device sits on the back of the rear mech and also turns the cable through 60°. Several different pulleys are available to compensate for the differences between all the most common combinations of shifter, mech and cassette.