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Someone shows you a bike with internal routing, and you marvel at all the advantages:

  1. you're not upsetting the tension by lifting the bike from its top or down tubes,
  2. there are no exposed sections of the cables, and hence no risk of chipping to the lacquer,
  3. cleaning the bike will be that much easier,
  4. there is no risk of dirt entering the cable housing near sections where the frame is used as the cable tensioner,
  5. the aerodynamics are better,

and perhaps other good factors. All in all this more than makes up for the added complexity of changing cables, which is in any case an uncommon maintenance event.

But then you ride the bike, and you hear very clearly the sound of a cable rattling with the frame when you're in certain gears. It's not loud, and it's not alarming, but, aside from tyres, you expect well-tuned bikes to be basically silent.

Is rattling unavoidable with internal cable routing?

Are there styles of internal cable routing?

A good, but now-deleted, answer suggested that there is more than one style of internal cable routing. The less-well designed (and offered at lower price points) bike frames apparently let the cable(s) loose inside the frame, as illustrated in the cross-section on the left of the figure. In this case rattling noises are inevitable, at least some of the time.

Better, higher-value frames introduce a special channel that enables securing the cable housing through foam or a similar method. I improvised how this might be done in the figure on the right.

If this is accurate, the question becomes how we can determine (from the holes, perhaps) how a given frame routes the cables, with the objective of predicting whether a silent ride is possible.

two cross-sections illustrating styles of internal cable routing in bike frames

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  • 3
    Do you mean rattling, rather than resonance? The latter has a specific meaning in physics, and people may associate resonance with speed wobble.
    – Weiwen Ng
    Sep 2, 2022 at 15:49
  • 1
    Many physical objects have natural frequencies at which they vibrate. If you input a force around that natural frequency, the vibrations will grow in strength, e.g. when you rub the rim of a wine glass. That’s resonance. If your cables are rattling, that’s just rattling.
    – Weiwen Ng
    Sep 2, 2022 at 17:48
  • 3
    @sam no sorry - resonance is a self-reinforcing oscillation based on a specific frequency. Rattling is not caused by an input vibration, just the fact of being loose.
    – Criggie
    Sep 4, 2022 at 1:58
  • 1
    The first step to understanding things is using standard words so that you can read what others have already written about the subject
    – ojs
    Sep 4, 2022 at 11:27
  • 1
    @Sam To be scientifically pedantic, that buzzing fly noise (I know what you're talking about) is just high-frequency rattling. As others have described, it doesn't have that additive, increasing-amplitude property that actual resonance does (think of an opera singer shattering a wine glass).
    – MaplePanda
    Sep 5, 2022 at 3:36

2 Answers 2

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The problems and solutions of rattling are well understood, whether the manufacturer wants to apply them or not is an another question. To save money (or differentiate ranges), a manufacturer may not implement all technical solutions.

Some entry level bike for instance can have fully internal cable routing, where nothing has been done by the manufacturer to attenuate rattling. On higher end bikes, you can have internal guides/liners in which cables/hooses can be fitted.

Generally speaking, derailleur cables should be under tension and should not rattle against the frame. But in certain gears (those for which the tension is the lowest), the cable has more amplitude when it oscillates and knock against the frame. Note that this problem might also exist with external routing, where cables can run even closer to the tubes, but bikes with internal routing are more likely to have thin hydroformed "tubes" (or carbon frames) while bikes with external routing have thinner but thicker tube, so less resonance. Also, entry points are typically the side wall of the down "tube", and the exit point is typically in the middle of the down-wall of the down tube. The cable is then the furthest from the wall at the point where the oscillation is maximal. Adjusting the tension in the derailleur cable can mitigate that.

The hardest to fix, to my opinion is the rear brake hydraulic hose, that is not under tension. If nothing is done by the manufacturer, the hose can move almost freely within the frame, and given it's quite hard to get inside the frame, doing something to fix the issue can be difficult. There are some tricks - like zip ties*, but these are only fixes and won't be as good as a well built frame. It's one of the many example where paying a visit to a shop is better than buying online: to be able check the play in the rear brake hose, better an external one than an internal where the hose is loose. To check, here's a simple tip: the try to move the hose "in and out" at the entry point. If it moves freely, already knocks against the frame, it's a guarantee to have unwanted noises when riding.

  • Others I've seen will seriously limit to the possibility to replace derailleur cables, if not prevent it.
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  • Nice answer. Two issues though: 1- "derailleur cables should be under tension and should not rattle against the frame." Well, yes, but the tension is against the cable housing, not against the frame. (And in internal cable routing the cable housing has complete coverage; there is no option to substitute the frame for compression in a segment.) Also, 2- it makes no sense for bike manufacturers not to announce the design differences, because 2a- it's unethical to not disclose what is basically a design weakness, and 2b- any factor distinguishing frames will push buyers to spend more.
    – Sam7919
    Sep 4, 2022 at 21:31
  • About your 1: I can't obviously answer for all frames, but on the frames I could have a look at, there's no housing inside the frame (for derailleurs at least). It wouldn't make sense to me to have housing inside the frame: derailleurs cables are light and under tension, so would not require it. Adding it will add weight, friction, and additional rattling. On your 2: on marketing, you often have cases where they announce good features, but don't say anything about the bad ones. But even so, a quite ride is expected from a quality bike, so maybe better to focus on topics that sell better.
    – Renaud
    Sep 5, 2022 at 5:29
  • Intriguing.. so when a derailleur cable is routed inside a frame, there are still two cable stops and a long, exposed cable. Basically how it would look outside, except that it’s now concealed inside the frame. Exercise to self: take a high intensity flashlight and inspect to see if at least the ferrules can be discerned.
    – Sam7919
    Sep 5, 2022 at 13:32
  • That manufacturers do/do not announce what’s right/wrong with their method of outside/inside cable routing may be perfectly accurate, but it’d also be very hard to swallow. You’re basically saying that caveat emptor applies to new bike purchases (for at least this issue). The principle applies for homes and for cars, and even then, only for the previously owned ones.
    – Sam7919
    Sep 5, 2022 at 13:32
  • @Sam: the elements that makes the difference between a premium product and an basic one are rarely on the spec sheet. To remain whithin the bike world: I have LX shifters on my trekking bike, and my fun bike had Acera ones, both are 9 speed. Just by operating them, you can feel that the LX are an upper range product: less pressure to shift, subtle 'click' to indicate an index shift, nicer feeling in general, even after 15 years. The Acera started to develop play due to the plastic parts, and a cheaper design. None of these characteristics could be guessed from the spec sheet.
    – Renaud
    Sep 5, 2022 at 14:06
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Internal routing is easily 40 years old with plenty of 1970/80s road bikes using it for rear brakes. Peugeot was one of the early adopters of it with great

There's actually loads of different types of internal routing and depending on which it will have different levels of vibration/rattling that the cables will experience.

Some bike manufacturers started putting soft foam cables inside the frames to stop cable rattling.

Note: I'm pretty busy now so will put the different types and links etc later

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  • I hope you don't mind that I modified the question slightly. Can you share what you know on this issue? It seems there is very little expertise around about it, and so anything you add on this topic will be enlightening.
    – Sam7919
    Sep 4, 2022 at 12:22

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