Tech Talk
by Jim Langley
If you bought a new road bike in recent years, you may have cables that are partly inside your frame, maybe your components, too. Known as internal cable routing, this feature is helping to create some of the cleanest looking rigs ever, and it also reduces wind drag significantly according to the gurus that run Specialized’s Win Tunnel.
I’m sharing photos that show some of the neat ways today’s bike designers are making cables all but invisible to the eye and mother nature. The photo of the orange bike shows a “trap door,” beneath the down tube. Removable ports like this in different parts of bikes let you get your hands inside for heading cables in the correct direction – rather than completely missing their intended path or exit point.
Cable protection, too
Internal cable routing serves another purpose, which is to protect the cables (or wires in the case of electronic components) from being snagged or severed in a crash, or if the bike falls allowing the cable or wire to strike something.
Because modern components, such as electronic drivetrains and disc brakes have made internal cable routing commonplace, it’s seen as something new. But, it goes way back on road bikes.
Bicycle cable routing made easy
My 1975 René Herse has internal brake and shift cables. What’s impressive about how Herse did it is that there are separate small diameter tubes inside the main frame tubes that the cables run inside.
This means that if you happen to break a rear shift cable on a ride, for example, you simply feed the cable into the hole at the top of the frame. Then as you push the cable at the top it goes through the down tube, around and through the bottom bracket, down the chainstay and exits near the rear drop out ready to attach to the rear derailleur. It only takes seconds.
Tip: I have a lot of photos of the bike showing the details here: https://jimlangley.net/ride/ReneHerseBicycle.html
Routing made difficult
I explained how René Herse did it because to me it’s the gold standard. Unfortunately, with modern internal cable routing, you often find that it’s nearly impossible to get the new cable to travel the right way just by pushing it through the entry hole. Where Herse made sure you could easily fix cables on the road, that may not be possible with many modern rigs.
A simple trick to help feed bicycle cables
To help, there’s a $10 “cheat” you can purchase and carry to save the day. It’s a small diameter hollow nylon housing liner made by Jagwire. It’s just the right size for many cables to fit through it. This is not for electronic wires, but for cables. And because they’re smaller diameter and used more, shift cables are far more likely to fail than brake cables.
If possible, leave the broken shift cable in place to start
To use the Jagwire liner piece to fix a broken shift cable, the first thing to know is that it’s usually easier to put a new cable in if you leave the broken shift cable in the frame to start. So don’t automatically pull it out. Typically, shift cables break at the ends, near the lever or near the derailleur. As long as it didn’t break inside the frame, it’s easier to leave the broken cable in place.
With the broken cable in place, all you have to do is to cut a piece of Jagwire housing liner that’s the right length to reach through the frame and come out on both ends. With the right length piece, you can slide it onto the broken cable from whichever end of the broken cable is easiest to access.
You don’t want to push the old cable out of the frame as you push on the Jagwire liner piece. You may need to hold the other end of the cable to keep it in place. Then carefully push the Jagwire housing piece onto the cable and keep at it until it’s out of the frame on both ends. You may need to wiggle the shift cable and liner a bit but the liner will go through if you keep at it.
With the liner in place, it’s a piece of cake to pull the broken cable out of the liner and slide the new shift cable through the frame since it’ll go straight through the liner.
If the shift cable broke another way, you’ll have to remove it and you won’t be able to slide the Jagwire piece through the frame with the broken cable guiding it. But, with patience and luck, you can usually get the Jagwire piece through – especially if there are ports in the frame to access it inside.
Once the new cable is running through the frame, pull to remove the liner piece and save it for future use. It’s only used for getting the cable in, not with the new cable.
Sometimes disassembly is required
On some bikes, the only way to reach inside and feed the cables is by taking things apart, like removing the fork to get inside the head and top/down tubes. Or removing the crankset and bottom bracket to get inside the bottom of the frame.
If you have a non ferrous frame, Park Tool makes their ingenious and extensive Internal Cable Routing Kit $65.95), a magnetic cable feeder/fisher tool that has saved the day many times in our shop.
Here it is in action.
Please share your great tips and tricks for fixing internal cables in the Comments.
I use the bright colored plastic weed Wacker line. Dirt cheap, I already have a supply and easier to see than the gear cable. I fish it thru first and then tape the cable to it and pull it thru.
Thanks, Mitch… cool tip!
Jim
From years ago: Put a sewing thread in the first opening, then suck it out the second with a vacuum cleaner. Tie it to the cable you wish to route and pull gently. Bike shop guys have been using this technique for as long as I can remember. Good luck. 🙂
Never done this myself but I have seen the same suggestion with dental floss instead of thread.
I use a length of small diameter tubing – a sort of sheath – to help guide the new inner cable (no problems).
For the first time I changed the cable myself yesterday. I found the cable had an internal sheath that had jammed tight onto the cable where it turns under the bottom bracket – presumably from repeated stretching and rubbing. Because of this the sheath was moving backwards and forwards with gear changes, and the top end where it exits the frame before going to the gear levers was jamming up against the end of the normal outer cable. As a result the end was heavily wrinkled and further jammed the inner cable. Gear changes became very hard, probably leading to the inner cable breaking yesterday.
My question is:-
Q 1a. Should the inner sheath remain on the inner cable through the carbon frame? or should it be removed after getting the new inner cable installed? (is this make/frame specific?)
Q 1b. If I leave the inner sheath on the cable inside the frame, does it need to be a particular type of sheath? e.g. teflon perhaps.
As well as the problems I can see advantages of leaving this sheath in position:- reducing the sound of cable slapping the inside of the down-tube, and possibly providing a reduced friction turn at the bottom-bracket.
In the best case (when the old/broken cable is still in the frame), I have had success taping one end of the new cable to the old cable and carefully pushing/pulling it through the frame. If tape does not work, I sometimes use a piece of thin tube/housing liner and heat the tube to seal the two cables together. When needed, I first use a long cable with no cable end piece (sacrifice cable) as the first cable to tape to the old cable and pull/push through…then tape the new cable to the sacrifice cable and push/pull the new cable through.
In the worst case (no old cable to work with), I mark the new cable with a scripto pen at the approx length to reach the outlet opening (measure outside the frame to get the approx length). I then insert the new cable to the appropriate length to reach the outlet opening and then use a flashlight and small hook made from an old spoke to catch/fish out the new cable at the outlet opening. This takes time and patience but will usually work if one does not have the Park Tool kit.
If some of the old cable is accessible,I use heat shrink tubing to bind the old and new cable together, then pull the new cable through the frame.