CABLE STRETCH-MYTH VS. REALITY

Ever had your bike worked on, had new derailleur cables installed, and had the mechanic tell you to come back in a week or two so he can adjust for "cable stretch"? It's a myth. Most good bicycle cables today are "Die-Extruded, Pre-Stretched" stainless steel cables. That means they are unlikely to stretch if installed properly.

Assuming the cables have been properly set-up to start, what does happen is that the outer sleeve of the housing tends to pull back from the ends. If you pull the ferrules off the housing ends, you'll see the wires starting to protrude. If you are still useing brass ferrules instead of the plastic supplied on most modern 4mm shift housing, the protruding wires will make a grinding, scratchy noise on the inside of the ferrules. When this happens, it has the same effect as if the cables had actually stretched. You'll need to adjust your derrailleurs to make them shift right again. Or better yet, pull the ferrules off and trim the exposed wires off the end of the housing. Or even better than that, replace the ferrules and housing, it's pretty cheap.

Cable housing doesn't stretch that quickly though. It should be a few thousand miles before it becomes a problem. If the derrailleurs were working well but started to shift poorly after only a few hundred or less miles, the culprit is usually the skill of the mechanic.

When the bike is set up, all cables and housing needs to be given a few good tugs before final adjustment. This is just to make sure that the ferrules are properly seated on the cable housing and in the frame stops, and that all the fixing bolts are tight. Go ahead and give it a good yank, you wont break anything that wasn't already broken. Then readjust the brakes and derrailleurs.

Now everything should run a long time without needing any particular adjustment so long as it's kept reasonably clean. Just don't forget that like most metals, cables will fatigue and should probably be replaced anually.

Any mechanic who tries to fall back on "cable stretch" is really covering for his lack of ability. Dont believe him. It's just an ugly rumor.