Road bike Gear Cables - How to know if my shifting will last?

Hey everyone,

I am using a road bike with internal cable routing and I have had over two instances where my gear cable (mostly rear derailleur) would fray or break during a ride, which will get me stuck in one gear. How do I know that I have some life left in my gear cables before it breaks?

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Usually before it breaks completely the shifting will begin to degrade and it might miss more shifts or feel very stiff. Physically checking the cable is hard with full internal routing unless you have an exposed section under the bottom bracket where you can check for wear.
Depending on how close together these incidences happened, I would suggest that maybe there is a fault in the cable run or in the shifter if you are braking cables quite regularly because for me a cable snap happens maybe once very two years.

I had the same problem and I couldn’t feel a degrading in shifting performance before the break.
Since then I change my shifting and breaking cables once every year.

I’ve had a rear cable to break at 1600 miles, and I’ve had one break at 2200 miles. I learned to replace them at 1500 miles. It takes 5 minutes, costs about $2 for zinc coated cables, and eliminates the worry about limping home with 2 gears.

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Odds are it will fail in the same spot every time. Inspect that spot regularly, or replace preventatively. I replace mine about every 3 months (usually at or near failure) and it take 5-10 minutes.

I’m seeing lots of “I replace cables at xyz”. When do you change out your housing? If you’re cable is breaking, no way you ought to be just replacing the cable. On my mtb, new cable & housing in early April & early August.

On a road bike, i change the rear cable every 3000 miles, and the front i just do every few years or so (ive only broke one fromt cable in the last 20 years) i only change housing when shifting just feels bad. Mountain and gravel bikes need the cable replaced sooner, i think ill do the gravel bike rear at 1500 miles. The best way ive found to track mileage is to add the cable im the “gear” section on strava, then you can know the mileage and reset each time you change

I’m a roadie rather than MTBer, but the cable normally breaks in the shifter (where there is no housing), as the cable is repeatedly wound and unwound over the shifter, and strands slowly fatigue and break as they are repeatedly bent and straightened. No need to replace the housing for this reason.

Yes, over time the movement of the cable back and forth in the housing will move grit through housing, and movement will also abrade the housing inner into small pieces, which will add to friction and decrease shifting quality, but this is a slow process and different from the cable breaking. Probably replace the housing once for every 2 cable replacements.

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Oh, I see, thanks for the info! I’ve got old Rival 10 speed stuff on a bike I didn’t & haven’t put much mileage on so I never ran into an issue like this. Good to know.

Yeah the main difference is that a housing swap on a road bike requires new handlebar tape also. So it’s much more straight forward on a MTB. Also, there is just less mud, dust, and grit on the road compared to MTB trails.

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Thanks I will keep this in mind. Not a lot of cable is exposed near the bottom bracket unfortunately.

Shimano tends to fray and break inside of the shifter and as someone said it’s not a terrible idea to change them on a regular basis, maybe every time you swap chains.

Not sure if this would help or not but I store my bikes with the derailleur in the most closed position where there is less tension on the clutch/spring in the derailleur. Not sure if it would also keep some tension off the cable too