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I'm upgrading an old folding bike (Dahon Speed). It currently has a 7 speed shifter and a Shimano 105 RD. However I haven't decided whether to stick to flat bar or change it to drop bar. I'm wondering if I can for now just replace the crankset with my spare 105 50/34 and continue to ride it like a 7sp while I'm shopping around the shifters and bars. Would it work? basically:

  • Shimano 7 speed trigger shifter
  • 7 speed cassette
  • Shimano 105 11 speed 50/34 crankset
  • 11 speed chain
  • No FD (waiting for the adapter)
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If you do it with an 11-speed chain on your 7-speed cassette, the rear shifting will be laggy, although once it's on a gear it will work.

The better way to do it is keep using a 7/8-speed chain, and space out the front chainrings a little to avoid rub and involuntary pickup. What I do that just works most of the time is use a Wheels Mfg 0.6mm chainring spacer on each chainring bolt. With FC-R7000 and FC-5800 you'll be doing it on the inner ring if you can so as to not disrupt the flowy 3d look of the outer ring and spider. Other companies make them in smaller increment sizes, and if that's what you come up with you can just use a stack. You're simply going for spacer equal to half the width difference of the chains in question.

Some Dahons have very short chainstays. That will exacerbate chainring rub if so. That's what the spacers are trying to solve, and they usually can, but short chainstay bikes are the situation where some trial and error tuning can be needed, so having the 0.1mm spacers to play with may be handy.

Always pair the FD you use to the chain speed generation to avoid problems with either rub or the cage gap being too wide.

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  • Thank you for the detailed answer. Do I still need the spacers if I don't install a FD and just keep it on the big chainring?
    – Ning Wang
    Sep 17 at 15:23
  • 1
    No, not the big. That said you will probably have a hard time keeping the chain from derailing without an FD. That's usually how that one goes. Sep 17 at 15:47
  • To circle back, yes it works flawlessly. Just swapped the crankset and rode it with no problem at all on the big chainring, with the original 7 speed chain as advised above. The small chainring does not work well, but I don't plan to tune it. This weird 7-speed 105 1x bike would serve me well until my 11 speed cassette and shifters arrive.
    – Ning Wang
    Sep 20 at 4:40
  • @NingWang Maybe saying "probably" is a stretch, it depends on other factors such as chainline and the RD in use, but I've had bikes set up similarly where it's a temporary 1x and had problems with chain drop when going over bumps etc. Sep 20 at 4:57
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To answer my own question, yes it works. Here are what I did over the past couple of weeks:

  • 11 speed crankset, 7 speed shifter/freewheel/chain, and 10 speed rear derailleur. Works perfectly.
  • 11 speed crankset, 11 speed shifter/cassette/chain, and 10 speed rear derailleur. Works acceptably as a temporary solution.
  • 11 speed everything. Works perfectly again. Now I'm just waiting for my front derailleur.

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