Daytrip

I was just starting out on my epic Saturday ride when my rear derailer cable broke. It just busted off right at the shifter. I aborted my ride, returned home and replaced the cable, but I'm curious how common that is. That particular cable has about 3,500 miles on it.

Does anyone carry spare cables in their seatbag? I'm sure I could change it on the road if I had to--at least enough to get home, so I'm thinking maybe not a bad idea.

Anyway, I was surprised. I would have expected more life out of it.

bdcheung

I replace my cables at the beginning of each racing season.

Primarily to avoid incidents like this.

10 Wheels

27,000 miles no broken cables.
2 spokes, one frame broke

Daytrip

But you put more than 3,500 miles on per season, don't you, BD?

Fred: I guess I'd rather break a $3 cable than a $$$ frame.

joejack951

I've heard of people having issues with certain shifters and cable breakage. I swapped cables on my old bike after ~10,000 miles and the right shifter cable had started to fray inside of the shifter. Your options are either carry a spare and be prepared to change it out or consider it a maintenace item and replace every 3000 miles (given your failure at 3500).

bdcheung

Don't really keep track of miles, so I can't answer that question accurately. But, 3500mi/52wks = 67mi/wk, and I'm pretty sure I do more than 67mi/wk, so I can say that I'm fairly confident I do more than 3,500 miles per year.

So my previous post is moot.

Are your derailer limit screws set such that there is high tension on them when they are in the largest cog/chainring?

Daytrip

^^^Don't really know. They stop the der where they should is about all I know for sure.

I guess from now on I'll just keep an eye on the cable to see how it's wearing (or not). Could be just one of those things.

I imagined myself as a fixie freak as I rode home in the highest gear. Of course, there's a big hill leading up to my house, so I got a reasonably good workout despite the brevity of the ride. But tomorow--look out world!

kayakdiver

It happens. I replace mine every year but a few months ago I broke the same one at the shifter. Bad luck is all I figure. And no.... I don't bring a spare.

Mr. Beanz

LIMIT SCREWS?

bdcheung

YES

Mr. Beanz

Limit screws have to do with tension on the cables?

bdcheung

Yeah. Think about it for a bit and if you still can't figure out how the two are related, I'll come back and explain.

AEO

The cables fray because of metal fatigue. that constant winding and unwinding in a tight bend causes them to fatigue.
if your high limit stop is set so tight that you are breaking cables, it's very unlikely you have the full range of your cassette.

I honestly think your shifter mechanism would break before the cable.

Flatballer

No need to take a cable with you. Just adjust the limit screws so that you've got a central cog, and then just ride home in that gear. Shift the front derailleur and you've got two gears to use.

Mr. Beanz

OK, 'splain! Liit screw to tight, no full range of gears. Too loose, allows the chain to move past outer or inner gear. Limit screw dictates the range of motion and movement allowed by the derailleur. If you've ogt the limit screw to tight, you'd never reach the end of the gearset, how is that putting enough tension to break a cable?

Barrel adjusters yes, limit screws?

ericm979

Shimano 10sp shifters go through cables quicker than 9sp did. They break where they bend around a drum in the shifter. I think the 10sp drum is smaller diameter than the 9sp one was.

But the hole in the lever cap that you use to insert the cable also works well as an inspection hole. Shift to the large cog (it's always the rear shifter cable that breaks for me), pull the brake so you can see the top of the lever, and shine a light in the hole. You can see the cable in the hole. If there are any broken strands its time to replace the cable. Mine seem to last about 3500 miles or so, but I shift a lot.

Usually I can tell the cable is starting to break because the shifting will get unreliable for some cogs in the middle of the cassette. I keep a couple spare cables at home in my parts stash.

simplify

I think I see what he means, so I'll take a stab. If you have your low limit screw (for example) set such that it wants to stop the derailleur just a little bit before it clicks into that biggest rear cog, you might put a bit of extra force on the shifter cable to pull the derailleur into that last click. Ideally, the derailleur should be able to move easily into the biggest cog, but not at all past it.

simplify

This is very good to know.

Mr. Beanz

The cable tension dictates how is shifts up and down, not range of motion.

Cable tension controls the movement of the derailleur, fast or slow and sluggish depending on tension. Shifters dictate amount of clicks/movements, eg. 7,8,9 10 etc.

If the limit screw is to tight at the low end, it just go into the big cog. Just as it won't go into the spokes when set properly or into the small cog if too tight or past teh small cog when the outter is set properly.

Daytrip

Yes, thank you for that explanation. That's exactly what happened. I thought maybe I had it installed incorrectly.

Thanks for that info, FB.

simplify

You're missing the point. It's nothing to do with cable tension. The cable tension is the same throughout the range of motion. The limit screw tells the derailleur when to stop, but there is always a little bit of wiggle room at the big cog. If it tells the derailleur to stop just a tiny bit before the final click onto the big cog, you'll push harder on the shifter to get the chain to hop up on that final cog. You can try this yourself if you don't believe me. The low limit screw is not absolutely precise, there is a little bit of "give".

This isn't about indexing, so it's not about cable tension. The indexing can be absolutely perfect, but if that low limit screw is trying to prevent the last click from happening, you'll push harder to make it happen.

BD, you wanna help out here?

Mr. Beanz

Oh, I know what you are talking about. That's the "ride a wheel with a broken spoke then wonder why the others broke later on" sydrome!

simplify

I guess you could say that.

I think AEO is right though, in saying that it would probably damage the shifter before it would break the cable. It does increase fatigue on both.

AEO

if you've ever tried the new campagnolo shifters, the front shifter will automatically shift down when the cable tension is too tight.
FD requires way more cable tension than RD, but that side rarely breaks its cables because you don't use it as often.

since it's snowing, next time you ride the rollers or trainer, try plucking the FD cable when you shift it, you'll see what I mean.

nitropowered

change at least the rear cable when you change your chain. Its usually the rear cable that breaks on 10s shimano shifters. I don't think i've seen a front cable break but its good to change those too, probably every two chain changes.