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The issue I have is that at the new bike I'm looking to purchase I'm faced with the followings:

  • the chain falls between the 2 chainrings of the front derailleur when shifting from the big ring to the small one (see also attached image).
    • this happens almost all the time when having the rear derailleur in the gears 9 to 6 (the ones farther away from the wheel).
    • in the gears 5 to 1 (the ones closer to the wheel), it works fine most of the time.
    • also this happens mainly when shifting the gears while riding the bike, not that much when the bike is on the bike stand.
  • last but not least, the chain never falls in between the chainrings when shifting from the small ring to the big one.

Some of the sales people told me that this happens because of using the 9-6 gears on the rear derailleur, and that one should not shift to the smaller chainring when in those gears.

Is this a normal behavior for a brand new bike? What can be the root cause of this, and how can it be fixed?

From my knowledge this should never happen no matter what gear combination is being used. And I suspect that the issue is either at the crankset, where the distance between the 2 chainrings is a few millimeters bigger than necessary, or with the chain itself.

The model I look into is Trek Zektor 2 with the following specs:

Shift Levers: Shimano Sora
Front Derailleur: Shimano 105
Rear Derailleur: Shimano Sora
Crankset: FSA Vero 50/34T
Rear Cogs: 9-speed

chain falls btw the 2 chainrings

Update (2019-04-16): the store ordered a new bike, same exact model, and this one shifts perfectly fine, the chain never falls in between the 2 chainrings. Everything is the same on the bike, except 2 components: the FD is now a Shimano Sora (instead of Shimano 105), and the chain is a Shimano HG53 9-Speed (instead of Shimano HG54 10-Speed). Therefore it turns out that the problem was caused by the chain being too narrow for the rest of the setup.

  • How's your chain length? Can you add a clear photo of the bike in big/big from the right hand side? – Criggie Apr 13 at 22:00
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    I kinda suspect that the chain is too narrow, or the chainrings have the wrong spacers between them. – Daniel R Hicks Apr 14 at 0:19
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    It's pointless to theorize about why this particular bike has a problem. There are plenty of Claris and Sora level bikes available. Just take your money elsewhere. – Argenti Apparatus Apr 14 at 23:24
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    @ArgentiApparatus the story behind is somewhat longer, I actually already payed for the bike, the price of the bike was, and currently is at 750 EUR. However I bought it on the opening day of the store when they had a special price of 450 EUR. I still have the option to get my money back, as I didn't take delivery of the bike yet, however I would rather wanna understand the issue, and have the bike store repair/replace whatever is causing the problem. Although at fault here I suppose is the producer of the bike, i.e. Trek. – Chris Dev Apr 15 at 9:27
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    Update: the store ordered a new bike, same exact model, and this one shifts perfectly fine, the chain never falls in between the 2 chainrings. Everything is the same on the bike, except 2 components: the FD is now a Shimano Sora (instead of Shimano 105), and the chain is a Shimano HG53 9-Speed (instead of Shimano HG54 10-Speed). Therefore it turns out that the problem was caused by the chain being too narrow for the rest of the setup as suspected by @DanielRHicks & Swifty. If you formulate that as an answer, I will accept it. – Chris Dev Apr 16 at 10:09
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This is not normal. Modern bikes should not throw the chain off the rings, either off the outside, inside or between the rings when changing gear.

The front derailleur is probably set up wrong. Don’t let the bike store staff tell you it’s normal. You have a choice here so just buy a bike that works right from the beginning.

It's true that you don't want to be cross-chained: on largest chainring and inboard half of cassette or smallest chainring and outboard half of cassette. That puts extra strain and wear on the chain, but the chain should not come off if you forget to follow this rule.

  • Thank you for confirming that the chain should never come off no matter the gear combination in use. Considering this, I assume that a bike store should not even be allowed to sell new bikes with such problems as this can turn into a serious issue when riding the bike in traffic!? The guys at the store tried to play with the FD for more than 15 minutes, however that didn't seem to help as the chain was falling in between the 2 chainrings, and not outside of them. – Chris Dev Apr 14 at 21:45
  • @ChrisDev When it comes to bikes, never assume that any new part is actually fit for the road. I've seen parts as critical as stems that were unfit by design. The problem is, the average bike part, especially when built into a BSO, rarely sees more than 100km of usage in all its life. That's probably the main market that these crap products are built for. Hardcore bikers like many of us enthusiasts around Bicycle Stackexchange, who easily cover more than 5000km per year, are rare, and simply not the target group of the BSO manufacturers. – cmaster Apr 14 at 22:00
  • @cmaster a bike with Claris or Sora shouldn't be a BSO - that's Tourney's job. I'd expect these groups to shift reliably, if not smoothly – Argenti Apparatus Apr 14 at 23:20
  • @ArgentiApparatus My comment was generic about the quality of new bike parts, and not aimed at the bike, parts, or manufacturer related to this question. – cmaster Apr 15 at 2:21
  • BSO = Bicycle Shaped Object. Thanks @cmaster I just learned a new term, I suppose that those supermarket bikes are usually such BSOs with a price tag under 300 EUR/USD. – Chris Dev Apr 15 at 9:43

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