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Replacing inner chain ring for lower granny gear

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Replacing inner chain ring for lower granny gear

Old 05-09-18, 09:09 AM
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gastonbe
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Replacing inner chain ring for lower granny gear

I just bought a Kona Sutra 2018 for touring and the plan is to drive it through Bolivia and Peru next week. This means a lot of mountains so I let the LBS change the chain rings to 44-32-24t. They didn't have a 22t ring unfortunately.

I'm pretty keen on getting a 22t chainring but I can't find a Shimano Deore one here in Santiago. I could only find a Shimano Acera chainring, made from steel:
Shimano FC-M391-22T Acera


I don't really mind the weight of a steel chainring and steel must be stronger than alloy? Still, any idea if it's a good idea to swap my inner chainring with this? Don't want to mess up my smooth shifting! I'm also worried about compatibility since Shimano doesn't list the FC-M591 crank as supported

Last edited by gastonbe; 05-09-18 at 09:32 AM.
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Old 05-09-18, 09:54 AM
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SkyDog75
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I don't see why it wouldn't work, especially on an inner chainring. The inner ring doesn't need any shifting aids like pins or gates since the chain will never be climbing up onto the inner ring. And since inner rings can wear faster and steel doesn't create much of a weight penalty for such a small part, some people prefer steel inner rings like the Surly stainless ones anyway.
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Old 05-09-18, 10:02 AM
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fietsbob
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in 5 bolt crank, you need a 58mm bolt circle granny gear , mounting..
if your crank has a 74mm bolt circle, 24t is as small as is possible to fit.

4 bolt the inner is 64mm so you should find them , if you search the web.

IDK if all the chainrings are riveted on..your particular part.




...

Last edited by fietsbob; 05-09-18 at 10:07 AM.
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Old 05-09-18, 10:10 AM
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gastonbe
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Originally Posted by fietsbob View Post
in 5 bolt crank, you need a 58mm bolt circle granny gear , mounting..
if your crank has a 74mm bolt circle, 24t is as small as is possible to fit.

4 bolt the inner is 64mm so you should find them , if you search the web.

IDK if all the chainrings are riveted on..your particular part.




...
I have a Shimano FC-M591 crank, but from what I've read many people have equipped 22t inner rings on it. Just not sure if this specific model will be a good choice.
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Old 05-09-18, 10:11 AM
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OK , and I cannot assure you from here..
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Old 05-09-18, 11:48 AM
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From the posts it seems that there is a 64mm bcd match between the crankset you have and the prospective ring. Steel is preferable for the inner ring and the inner ring does not need to be particularly sophisticated as far as profiling is concerned so Acera should be fine. Stainless steel mentioned by SkyDog75 is iffy as you optimally want tool quality steel in the application and stainless is mechanically inferior to better quality carbon - still it is better than alu.
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Old 05-10-18, 06:42 PM
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Have you calculated the gear inches to see how much lower a 22T would be than the 24T? It might not be worth the trouble of finding the part and making it fit. That said, I do have a steel 22T freewheel cog adapted to fit on my homemade "K-Mart triple."
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Old 05-10-18, 07:04 PM
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The new ring can't be that expensive, so perhaps just buy it and try it out.

However, before doing so, there are a few things that I'd probably do.
  • Shift into the big/big combo. How stretched out is your rear derailleur?
  • Now shift into the small/small combo. Does the rear derailleur still have some capacity left? I.E., not folded back on itself, with the chain dragging across it, or even hanging loose?
  • With the chain in the small/small, now look at the front derailleur. How close is the chain to rubbing the bottom of the front derailleur? Do you have at least about 3/8" clearance?
There is some fudge factor, and perhaps more adjustments that can be made, but the answer to those questions will help you decide if you can actually support a smaller chainring.
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Old 05-12-18, 06:08 PM
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You won't be able to tell the difference about the few tenths of an ounce that the steel ring will make and it will last much longer in hard service.
If you are doing loaded touring the only weight you should be concerned about is the gear you are carrying.
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