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Exceeding total capacity of rear derailleur by 1

Old 08-15-17, 06:50 PM
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Exceeding total capacity of rear derailleur by 1

I have just ordered a 26-36-48 9-speed Deore trekking crankset and plan to use it with a Deore M592 rear derailleur and a 12-36 tooth 9-speed cassette. The M592 has a total capacity of 45, and if you do the math, with a 12-36 tooth cassette, I will be exceeding the total capacity by 1 tooth.

I think it should be okay, if I use a 116 link chain and stay away from cross chaining, but does anyone have any advice or tips?
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Old 08-15-17, 09:56 PM
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it probably will work and you will see. you may have to shorten the chain so much that you can't cross-chain large-large, but that is an easy sacrifice.

I'd say since you already ordered, nothing we can advise at this point.
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Old 08-15-17, 10:13 PM
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Size the chain Big:Big +1 ".
You'll have a bit of chain sag in the 1-2 smallest cogs when on the small ring.
Since it would be abnormal to use those combos anyway, you'll be fine.
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Old 08-15-17, 10:17 PM
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I would take a different approach. Set the chain length so you can just cross-chain without anything bad happening, Note what happens when you go into the small-small gear. You may have slack chain, a derailleur cage that is completely folded back on itself and lots of noise but if it actually runs, just go with it. (The small-small gear may be unusable anyway because the chain may hang up on the middle chainring and want to shift.)

That way you are unlikely to have anything bad happen with either cross-chain. Just lots of noise/ perhaps attempted front shifts with small-small. So when you do cross chain, it doesn't turn into a very bad day. (Notice I said "when". If you ride, you will cross-chain unless you are willing to obsess about not cross-chaining. Especially if you get into riding hills and riding harder.)

Edit: my post was written before Bill posted his. I agree completely.

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Old 08-15-17, 10:22 PM
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Originally Posted by Bill Kapaun
....
You'll have a bit of chain sag in the 1-2 smallest cogs when on the small ring.
....
+1

There's usually some fudge room in derailleur capacity ratings. But if not, the worst case if you size the chain right is some droop when using the granny with the outer one or two (if that) rear sprockets.
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Old 08-17-17, 04:06 PM
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It turns out that the 2014 Surly Ogre and the Surly Troll, as well as the 2014 Troll had the exact same 9 speed spec, but with the old HG61 cassette instead of the HG400.

Strangely enough, they came stock with a SRAM PC-970 9 speed chain. Assuming the chain was 116 links, does anyone know if there was anything special about that chain used with Shimano components or did Surly just get a good deal on SRAM chains?
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Old 08-18-17, 12:20 PM
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Originally Posted by PDKL45
Strangely enough, they came stock with a SRAM PC-970 9 speed chain. Assuming the chain was 116 links, does anyone know if there was anything special about that chain used with Shimano components or did Surly just get a good deal on SRAM chains?
That's the second time that you mentioned the chain having 116 links. DOESN'T MATTER. Chains come too long for common usages and have to be shortened to fit most bicycles.

I subscribe to the big/big +1 school of chain sizing. That's the shortest chain that will safely work with your bike and gearing combination. It's easy to forget yourself and accidentally shift into the big/big. Doing that, even once, can cause a bunch of damage to your bike so you have to protect yourself from that.

If, like me, you use a triple crankset, there is no concern about chain wrap capacity because you'll never accidentally shift into the little/little and probably never even come close. I never use the little chainring with any but the largest couple of rear cogs so I never test my derailleur's slack take up capacity.
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Old 08-19-17, 07:12 AM
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Originally Posted by Retro Grouch
That's the second time that you mentioned the chain having 116 links. DOESN'T MATTER. Chains come too long for common usages and have to be shortened to fit most bicycles.

I subscribe to the big/big +1 school of chain sizing. That's the shortest chain that will safely work with your bike and gearing combination. It's easy to forget yourself and accidentally shift into the big/big. Doing that, even once, can cause a bunch of damage to your bike so you have to protect yourself from that.

If, like me, you use a triple crankset, there is no concern about chain wrap capacity because you'll never accidentally shift into the little/little and probably never even come close. I never use the little chainring with any but the largest couple of rear cogs so I never test my derailleur's slack take up capacity.
I only mention it because my newly replaced chain is 114 links long and it is too short for my current 30-39-50 crankset with 12-36 cassette, which worked perfectly with a 116 link chain, so to me it is of current concern. I am not riding "most bicycles," I am pushing my drivetrain to the outside of the envelope so to speak.

I am sorry if I offended you by mentioning chain length twice, but it's something I am acutely aware of at the moment, having forgotten myself momentarily and shifted into big/big with a new chain which is not long enough and needs a couple more links.

*Edit: I didn't understand the big/big+1, Googled it and understand it. I was merely thinking in terms of 116 link chains because that is what Shimano recommend with a 26-36-48 crankset on an 11-34 cassette. However, I will drop it for now, having done a little more homework.

Lastly, I would also appreciate answers provided without the use of the caps lock button, as it can offend. I am sorry if I appeared ignorant, and I may have been, but I do not believe it warranted such a response. I was merely seeking advice.

Last edited by PDKL45; 08-19-17 at 08:00 AM.
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