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Cable-travel adapters use a double, side-by-side 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. Links to manufacturers' lists of applications are at the end of this article.
The table below gives cable travel ratios for Shiftmate adapters from JTek Engineering and for the Problem Solvers Travel Agent. These adapters may be used in either direction, to increase or decrease cable travel. Note that the numbering of the JTek Shiftmate adapters does not increase in the same order as the ratios. Also, I have some question as to whether all of these ratios are correct. There may be an inconsistency on the JTek site regarding the Shiftmate #4. I have an inquiry out. Stay tuned.
|Shiftmate #1, 1S||1.051||100°, straight|
|Shiftmate #2, 2S||1.108||100°, straight|
|Shiftmate #3, 3S||1.199||100°, straight|
|Shiftmate #4, 4S||1.246||100°, straight|
|Shiftmate #5, 5S||1.320||100°, straight|
The article on adjusting direct-pull cantilever brakes on this site describes the use of the Travel Agent adapter so these brakes can be used with brake levers intended for other brakes.
A small-diameter pulley causes metal fatigue of the cable, and sooner or later, cable failure. The larger-diameter pulley of the Travel Agent is marginal in size to avoid this problem. The Travel Agent's smaller pulley and all of those on JTek adapters will fatigue cables. Shifter cable failure generally doesn't lead to a crash, and most shifters include a small-diameter pulley anyway. Brake cable failure easily can result in a crash.
The article on cables on this site gives more details about cable fatigue.
A pulley can reduce cable friction compared with cable in a housing, when taking the cable around a corner. The JTek angled pulleys do this at the rear derailer. The Travel Agent pulley is useful on bicycles with cables that have more bends than usual, for example on Bike Friday travel bikes, and often without using the ratio-changing feature.
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