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I wonder about such setup as buying 48/36/26T crankset and then replacing the smallest (26T) chainring with 22T one.

What I am afraid of that I would get quite significant 14T in difference and when shifting from 22T into 36T I could damage the chain.

So, is such mix -- 48/36/22T -- pretty safe or replacing the chainrings is only for actual replacing the used one to new, but exactly the same size?

  • I've a feeling that cheaper cranksets often have all three chainrings riveted together, which means you can't really swap individual rings in and out. – David Richerby Nov 12 '18 at 17:57
  • @DavidRicherby, that's correct, but all it takes is make sure you buy those with replacable rings. – greenoldman Nov 12 '18 at 19:06
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    4 teeth difference is not a lot. You might have some problems with derailer range, but aside from that it should work. It will be more stressful on the chain, but not much more. – Daniel R Hicks Nov 12 '18 at 21:39
  • Have you considered increasing the cassette size? Its easier, often cheaper and a more reliable way to get lower gears. Only reason not to is increased spread between gears. – mattnz Nov 13 '18 at 0:08
  • @mattnz, spread is exactly my point, my current cassette is 9-speed 11-34 and the spread is too big for my needs, I tested 12-26 and it works my smoother (on average the difference between cogs is 110%), so now I would like to pick up the crankset for such cassette (i.e. with lower gears). – greenoldman Nov 13 '18 at 15:59
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I'm going to answer with regard to putting smaller-than-stock small rings on a triple crank in order to get lower climbing gears. Doing it with the middle and large rings presents other challenges.

It's possible, and a lot of people ride setups like this. Here are some hitches you may encounter:

  • You may, and often will, exceed the rear derailer's 'Total Capacity' number. One of a rear derailer's jobs is to keep the chain tensioned over all the gear combinations. Total Capacity defines how wide of a gear range a given derailer is able to do this for. What this means in practice is that when the chain is long enough to cover the large/large combination safely, which it always should be, it will be slack in some number of the small/small combinations. Riding in these gears introduces a risk of derailment or jamming since the chain is more free to bounce around. A lot of cyclists decide they're fine with that risk and just stay out of those gears, which works well with the habits of most touring and utilitarian cyclists in particular since for them the small ring is mostly just for steep climbs. The exact same concern arises when you try to get your lower gears by putting on a bigger cassette, only in that case you also need to lengthen the chain.
  • Current (I'd say 'modern' but I hold out hope for the pendulum swinging back the other way someday) triple front derailers can have pretty specific chain contact points sculpted into them, and they correspond with the ring combinations they're designed to be run with. And middle chainrings have shift-assisting features (ramps and pins) that expect the chain to come off a specific inner ring. When people talk about how getting smooth front indexed shifting relies on all the components being designed to work as a system, these are some major pieces of that. You will tend to lose some shifting performance for these reasons if you put on a smaller inner ring. Usually it will be in the realm of still working, but just being more sluggish, clunky, and finicky to adjust and keep adjusted. It is definitely something of an experiment every time, which is a reason shops may be reluctant or unwilling to do it.
  • Friction front shifting handles this kind of setup much better because you have more freedom to finesse it. STI in particular is clumsy to intentionally overshift. It can be easy for performance to feel mediocre or compromised when you do this on a bike with STI.
  • I don't know all the reasons, but bikes set up this way are often more prone to chain drop on the downshifts. Using a simple plastic chain catcher of the dog-tooth variety is a good idea and usually solves the problem more or less completely.
  • Thank you very much, now of course I am curious what are the other challenges for changing only the biggest chainring, because as for riding middle gear is less important to me (biggest is for road, lowest is climbs and middle is well middle ground). – greenoldman Nov 12 '18 at 17:51
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    With the big ring, it needs to be at least a reasonably good match with the profile of the front derailer cage, which assuming front indexing can lead to wanting to go to a road front derailer and keep a mountain shifter or vice versa, which works badly. (There are many questions here about this). With the middle ring, front derailers have a spec called "minimum difference between middle and top" that needs to be respected or else the derailer will hit the middle ring as it passes over it. – Nathan Knutson Nov 12 '18 at 17:56
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The big jump between middle and small rings is going to give you shifting issues.

Additionally, you will probably exceed the total capacity of the front and rear derailleurs.

The total capacity of the rear derailleur is its capacity to take up chain slack. The slack you need the derailleur to handle is: (difference in tooth count between largest and smallest chain rings) + (difference in tooth count between largest and smallest sprockets).

The total capacity of a front derailleur is just the difference in tooth count between the largest and smallest chain rings.

If you are looking for lower gearing, better to replace the whole crank with a 40-30-22 (or just the rings, if smaller ones will fit on your existing crank).

  • Thank you, but I am confused with your latest remark "just the rings", this is what I ask about in general -- I need lower gearing but only for climbs, this is why I asked about replacing only the smallest ring. – greenoldman Nov 12 '18 at 17:53
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    @greenoldman For reasons on my answer, you will not be able to replace just the smallest ring with a substantially smaller one, you'll have to replace all the rings with a smaller set. To do this you might have to replace the whole crankset. – Argenti Apparatus Nov 12 '18 at 20:23

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