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Cable Travel Adapter Cribsheet

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by John "Ratios" Allen
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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 lists of applications are below.

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Adapter ratios

An adapter may be used in either direction, to increase or decrease cable travel. The table below gives specifications for the Problem Solvers Travel Agent. Thorn bicycles, new owner of JTek, has published a table listing tested combinations and asks that people interested in unconventional ones .

Adapter Ratio Angle
Travel Agent 1.911 90°

For some reason, manufacturers of internal-gear hubs do not make drop-bar shifters for them -- but there are solutions:

Pulley adapters are not intended for use with internal-gear hubs. The steps in cable pull of most such hubs are uneven, and so only dedicated shifters will work. (See our internal-gear hub cable travel cribsheet for the messy details).

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Applications

See the article on mixing and matching shifters, derailers and sprocket spacings on this site.

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 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.

A small-diameter pulley causes metal fatigue of the cable, and sooner or later, cable failure. The larger pulley of the Travel Agent is large enough mostly to avoid this problem. The Travel Agent's smaller pulley and all of those of JTek adapters will eventually fatigue cables. Shifter cable failure generally doesn't lead to a crash, and most shifters already include a small-diameter pulley. Brake cable failure easily can result in a crash. Every bicycle should have two braking systems!

The article on cables on this site gives more details about cable fatigue.

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Links

Jtek Engineering home page

Jtek Engineering Shiftmate compatibility

Problem Solvers Travel Agent page

Dr. David Gordon Wilson on cable fatigue

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Articles by Sheldon Brown and Others


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Last Updated: by John Allen