By Scott Wilson
Editor's Note: Special thanks to The Bike Lane for lending their expertise to this article!
As I mentioned in the previous article, the key to getting the best possible shifting and smoothest breaking is to have fresh, well-prepared cables and housing. In this article we’ll go over how housing is properly installed, but I’ll also show you some tricks that will lengthen the lifespan of your housing. For this article, Adam, one of the mechanics at The Bike Lane, graciously provided his knowledge and the shop provided the scenery. The goal of this piece is to give you a solid understanding of what the mechanic is doing with your bike and money, but if you want to use this article as a supplement to a how-to, that’ll work.
If you want to do your own cable replacement, normal diagonal sheers like the kind you see near the hinge on a pair of needle nose pliers won’t have the bite to cleanly snip through stainless steel cables and housing. You need hardened, purpose-built cable cutters, and a good pair will set you back about $50. You’ll want a sharpened spoke or similar poking device too. And a bench grinder or file is necessary for preparing brake housing. A tape measurer will come in handy too.
Due to the high cost of quality cable cutters, I like to protect my investment with occult methods:
The basic rule for measuring housing is that you want to use as little as you can without impairing the function of any other component. What this means for every component is different, so here’s a quick rundown:
Cut the housing just short enough so that you can turn the handlebars all the way to the left and right without binding or kinking. If you think you might raise your handlebars, add a little extra length. It’s better to have too much housing than too little.
Here’s Adam measuring before cutting:
The trick with brakes, whether they be front or back, is that the housing should go straight out of the barrel adjuster for about two thumbnail lengths before any kind of bend.
This one’s too short:
This one’s too long:
The front brake housing should go straight down to the brake with a nice parabolic curve to the handlebar, like so:
Avoid having the front and rear housing touch when the handlebars are straight, or else they’ll make creaking noises when they get dirty and rub against each other.
Rear Derailleur Lasso:
In the previous article we learned that tight bends tend to wear housing out quickly, and the rear derailleur housing is usually the tightest bend on the bike. You don’t want the housing to enter the rear derailleur with any angle to it at all or it will put stress on the ferrule –the end cap. If the ferrule is plastic the little shifter wires will bust out the side. If the ferrule is metal the housing will kink just before entering the derailleur. There is a mathematical formula for finding housing length based on where the frame stop is in relation to the derailleur hanger, but it’s really boring and doesn’t account for design differences in derailleur models. Look up “outer housing length chart” if you’re curious. A Shimano tech rep once told me that you want the length of two thumbnails of straight housing right at the barrel adjuster and again at the point where the housing enters the frame. This isn’t possible on certain frames, like the Trek Domane and Cervelo R3, where housing exit hole is so close to the rear derailleur that the best you can do is trace an oblong half-circle. In my experience, bikes fresh out of the box from Taiwan or wherever they were assembled almost always come with too short of rear derailleur housing. If you’re trying to figure out why your new bike is having shifting issues within the first hundred miles that can’t be resolved by fiddling with the barrel adjuster, the rear lasso is a good place to start your investigation.
Here are two good examples:
In the last article I talked about how shift housing wears unevenly when subjected to a sharp bend, so that some of the wires at the ends will start to poke out beyond the plastic. To help mitigate this issue, the mechanic will bend the derailleur housing prior to cutting it.
Before a cable is ever run through a piece of housing, there are special preparations the mechanic does. Both brake and shift housing need to be perfectly flat at the ends. For shift cable that’s easy: just snip the housing perpendicular to the cutters, using a straight edge or the corner of a table as a guide. The inner plastic sometimes gets pinched, so a sharpened spoke or similar pointy thing will open it back up.
And here’s what the end should look like, with an aluminum ferrule:
Brake housing is tricky. Here’s what a freshly cut piece of brake housing looks like:
That metal gnarl there at the end will make the brakes feel terrible when it scratches against the cable. In this case the mechanic will probably cut the end again to make it cleaner, but then he’ll take it to the grinder:
And the finished end will be flat so that it sits evenly against the ferrule:
A Note on Ferrules:
Brake and shift housing have different outer diameters, so they need different ferrules. Brake ferrules are almost always made of metal, usually a steel alloy. Some brakes don’t require a ferrule.
Shift housing gets weird though: there’re plastic, aluminum, and brass ferrules. There’re ferrules with noses. There’re ferrules that are keyed to a specific component. And there’re special rules for when and where you should use each type of ferrule. These rules vary from manufacturer to manufacturer, of course, so it’s best to check the manual or ask a company representative. Generally speaking, you use plastic ferrules whenever the housing ends are pressed against the frame so that if the cable gets a little loose the rattling ferrule won’t scratch or chip any paint. Another time you might use a plastic ferrule is if the component you’re connecting the housing to is plastic –the hard ends of metal ferrules can dig into the soft plastic and create play over many years of use. Again, refer to the owner’s manual. Before putting a ferrule on a cable end I like to add a dollop of brand-specific cable grease to the inside.
Putting the housing onto the bike is easy, just fill the holes in the frame and components with one end of the housing or the other. Finding the right holes on some shifters is tricky, so I like to thread a cable through first. Before you do that, always shift into the smallest cog on the front and rear shifters. It’s easier to get the cable through that way.
Once you get all the housing on and the cable routed and secured with the fixing bolt, but before you tune anything, squeeze the brakes and give the shift cable a tug. This will press the housing into the ferrules and prepare the system for final adjustments.
A note on frames with internal cables or housing and no internal guides:
This stuff is best left to the professionals and their specialized tools. But if you must do it yourself, get a powerful magnet, a spoke bent into a hook, and a small LED light that can fit into tight spaces. Basically, you’re going to thread the cable in first and let it get picked up by the magnet on the outside of the frame, near the exit hole. Then you search for the cable with your LED and grab it with the hook. Use that cable as a guide for the housing. Professional internal routing kits work a little differently and make the job easier, but with practice the method above works fine.
Last step, tuning your bike:
That’s a massive topic we’ll save for another article. Thanks for reading!
Scott Wilson is an MFA writing student at Columbia College as well as a seasoned professional bike mechanic. Scott’s “wrenching” experience includes bike shops, racing teams, and professional triathletes across the US. The aim of Scott’s technical articles is to explain in detail how bicycles and their individual components work...and in doing so, help you keep your own bikes running better and lasting longer.