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My bike's recently been in for a service so afterwards I checked that all the gears are shifting and working properly.

As part of my testing I put some power through the cranks in the photographed gear and found that the chain slipped. Having found that out, I tested it some more and it's very easy to get the chain to slip in that gear by putting some power through it.

Is that normal? Could it be the derailleur set up at fault?

I don't ever use this gear day-to-day so it doesn't really matter I suppose. However, I'd like to think that everything was 100% working okay having paid for a service.

Should a service leave a bike in this kind of state? The bike's 11 months old and hasn't been heavily used in that time.

gear demonstration

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    First of all, you should never use this gear. Thou it's not should slip while drivetrain is new, it's relatively quick damaging cogs to slip. – Alexander Sep 20 '14 at 20:01
  • I never use this gear, except for when testing that my service has been done properly. Updated the question to be more clear about that, thanks. – Matthew Sep 20 '14 at 20:04
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    If it has just come back from the shop, I think you have a right to take it back and ask them to take another look. It's correct to say that this gear shouldn't be used when cycling, but equally it shouldn't slip. That looks like its only a 9sp cassette so should not be beyond their ability. – PeteH Sep 20 '14 at 20:50
  • What exactly did the service entail? – Batman Sep 20 '14 at 21:02
  • You're cross-chaining -- don't do that. – Daniel R Hicks Sep 20 '14 at 22:59
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In that extreme cross chain configuration you have the maximum amount of chain for the derailleur to take up. And you also have the least amount of chain tension. Combine that with on the least number of teeth engaged and you have the configuration that is most likely to jump.

Should it jump no.

It is a shop problem - maybe.

In just 11 months the spring in the derailleur could have weakened.

Or if you ride on the small gear in the rear even a bit it will wear and new chain might skip. But given it does not skip on other front gears I would chalk it up to chain tension.

The shop may have too many chain lengths. In biggest front and rear could a chain length be removed?

Cross chaining a road bike or the first two chain rings is something that happens. But on a mountain bike in the granny gear that extreme cross chaining is just not something that should come up. I would not put that kind of stress on a chain even to test.

Some front derailleur have a trim for big to big. This make sense to me as you may come to a stop but will get back up to speed soon. And now you have maximum teeth evolved. I don't know if trims comes in a 3 speed and it would make less sense as the outer is out further. Even with a trim cross chaining puts more stress on the chain and other components and is not as efficient.

The question is not about specifically about cross chaining but here is a link.
Technical Details and Implications of Cross Chaining

Not the question but the smaller rear gears are going to wear the fastest as they share the load across fewer teeth. So go for a larger front ring when you have choice. But still avoid cross chaining (a lot).

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There's nothing wrong with crosschaining with the modern drivetrains, despite what you might read in the comments. In fact, many modern drivetrains are specifically designed to help you to crosschain (like "trim" feature on some front shifters). The ability to use all cassette cogs without having to switch chainrings is too valuable to be given up because of some negligible increase in mechanical stress and wear due to crosschaining. The issue of "crosschaining" was left behind and forgotten back in 1990's.

However, it is important to remember that you can still run into mechanical limitations when crosschaining. It all depends on the geometry of your drivetrain. The most well-known one is the chain interference with FD cage or chain interference with the bigger ring. Do you get any of these? I assume you don't since you would be able to hear that immediately.

If not, then the next issue you might be experiencing is the lack of RD capacity. In this small-small configuration there's lots of extra chain the RD cage has to pick up. If the capacity is insufficient, then you might get chain interference at the RD cage, which might cause many different unpleasant effects, including skipping. Another consequence of insufficient RD capacity is loss of chain tension in small-small combination, which can easily lead to skipping.

So, what does your RD cage look like in this gear combination?

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    Given the information I can find on cross chaining, you'll need to provide some evidence to back your assertion that the issue was "left behind and forgotten back in the 1990s." – Carey Gregory Sep 21 '14 at 5:14
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    Cross-chaining small to small is almost worse on modern indexed drive trains since on both the front and rear the chain is being brought close to the adjacent cog. On a 10-speed rear the clearance is so tight that the chain can easily hook the ramps of the adjacent cog and try to "climb". It's not going to change gears, of course, but it can climb enough to chatter or slip a tooth. This is exacerbated because the chain is at its loosest. One could "tune" the setup to minimize this issue, but it would be at the expense of smooth operation in more reasonable situations. – Daniel R Hicks Sep 21 '14 at 11:51
  • @Carey Gregory: It is hard to "provide evidence" for something that is a basic fact. It is like asking to "provide evidence" that 2+2 is 4. Just look what pro-racers do. But in any case a solid piece of evidence is right there in my answer and has been there from the very beginning. (For some reason you decided to conveniently ignore it.) On more time: drivetrain manufacturers have been implementing "trim" feature in their FD specifically to facilitate crosschaining. And if with mechanical derailleurs this feature was sort of an oddity, with modern electronic FD this feature is a natural must. – AnT Sep 21 '14 at 17:23
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    Providing evidence for basic facts is easier than providing evidence for complicated ones. For example, one can definitely prove that 2+2=4 (just google it). You say all the pro riders cross-chain. Well, if that's true then it shouldn't be hard to find examples of racers doing it or at least someone reputable talking about it. For example, if cross-chaining became the norm in the 90s then there must have been debate about it at the time. The internet is a vast repository of debates dating back to the 1980s, so if there was debate then it can be found now. – Carey Gregory Sep 21 '14 at 19:48
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    There is no debate here. It's your answer and it's up to you to support it with credible references. I find it very hard to believe you can't find anything. – Carey Gregory Sep 21 '14 at 22:46

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