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Discussion Starter · #1 ·
...and a 12-27 setup or close to it... Most of you running this or similar setups along with a chainring combo in the area of 42/32/20, how is this possible? According to my calculations (42-20=22; 27-12=15; 22+15=37) if the short cage has a total capacity of 29T then this setup would be way over. I realize that the total capacity figure from the manufacturer is usually a little conservative but, not by that much. I also understand that you need to account for 'chain growth' that is inherent in most FS bikes. What I mean by that is, as the bike compresses the frame's center from the BB to the center of the axle elongates which effectively reduces your drive train capacity as your chain gets shorter through the compression stroke. Basically, as you ride, your FS is doing its thing and your chain is getting longer and shorter as you bounce along the trail. So, what am I not getting here?

Cheers,
Sean
 

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jakeplazma said:
...and a 12-27 setup or close to it... Most of you running this or similar setups along with a chainring combo in the area of 42/32/20, how is this possible? According to my calculations (42-20=22; 27-12=15; 22+15=37) if the short cage has a total capacity of 29T then this setup would be way over. I realize that the total capacity figure from the manufacturer is usually a little conservative but, not by that much. I also understand that you need to account for 'chain growth' that is inherent in most FS bikes. What I mean by that is, as the bike compresses the frame's center from the BB to the center of the axle elongates which effectively reduces your drive train capacity as your chain gets shorter through the compression stroke. Basically, as you ride, your FS is doing its thing and your chain is getting longer and shorter as you bounce along the trail. So, what am I not getting here?

Cheers,
Sean
Good Q Sean. The specs are conservative, as well as you'll have to be disciplined enough NOT to shift into the extreme large combos, i.e. big ring and 25 or 27 cogs. You wouldn't do that anyway right? Set the chain length to work for the 23 cog and big ring. You'll be fine. I run this setup on all my bikes.
I also run a 11/32 in a 1x9 setup with a 32 in front using a DA 7800 rear. Works great. Took a risk here, but it worked out. I had to set the tension screw back a ways to get the drop i need to clear the 32 cog.
Good luck.
 

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oooops - NO!

rensho said:
Good Q Sean. The specs are conservative, as well as you'll have to be disciplined enough NOT to shift into the extreme large combos, i.e. big ring and 25 or 27 cogs. You wouldn't do that anyway right? Set the chain length to work for the 23 cog and big ring. You'll be fine. I run this setup on all my bikes.
I also run a 11/32 in a 1x9 setup with a 32 in front using a DA 7800 rear. Works great. Took a risk here, but it worked out. I had to set the tension screw back a ways to get the drop i need to clear the 32 cog.
Good luck.
never have your chain shortened that much that it won't take a gear! that asks for major disaster...

i on the other hand have my chain shortened so that it just does the big/big gear (42/27). the rear derailleur is streched all the way but the cranks and wheels are still turning. in the opposite crossed gear low/low (20/12) the chain is loose indeed. but that's a gear you hardly ever use anyway. and as soon as you have the slightest (!) pressure on the pedal the chain is tensioned. you don't do any downhills in thise gear, don't you;) that's the way you have to setup your bike with DA! i'm riding my bike since 5 years this way and never had a chain falling off or any strange thing happening because of that setup. works perfect.
 

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Discussion Starter · #4 ·
Wow! I love this forum... Ask and most of the time you shall receive.

Rensho,
I tend to agree with Nino in that having your chain that short is definitely a recipe for disaster. Yes, shifting into the extreme combo's is unlikely but mistakes do happen. Why risk it? Anyay, your input is appreciated, thanks!

Nino,
I guess the total capicity figures are that conservative if it's working without any hicups. So, if using a rear der other than the DA with a total capacity of say 37T then this setup should work too, right? As always, thanks for playing!
 

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Use the GS version

jakeplazma said:
...and a 12-27 setup or close to it... Most of you running this or similar setups along with a chainring combo in the area of 42/32/20, how is this possible? According to my calculations (42-20=22; 27-12=15; 22+15=37) if the short cage has a total capacity of 29T then this setup would be way over. I realize that the total capacity figure from the manufacturer is usually a little conservative but, not by that much. I also understand that you need to account for 'chain growth' that is inherent in most FS bikes. What I mean by that is, as the bike compresses the frame's center from the BB to the center of the axle elongates which effectively reduces your drive train capacity as your chain gets shorter through the compression stroke. Basically, as you ride, your FS is doing its thing and your chain is getting longer and shorter as you bounce along the trail. So, what am I not getting here?

Cheers,
Sean
I use an RD-7700-GS rear derailleur (i.e. Dura-Ace 9spd triple) for a 12-27 cassette with 42/30/20 tooth rings. The capacity is 38 teeth and I'm using 37. Only been on this for a few weeks but it is better than what I have on my trail bike: 44/32/24 x 11-32. The finer shift increments are great when cresting a hill and having the chain farther away from the ground is a bonus. In fact there is no drawback to this setup that I have detected. I do get a touch of noise in the 2 fully crossed positions gently reminding me about chain wear.

If you are contemplating this type of setup consider doing it with a 21t ring on 4-arm cranks - your ring choices and replacements may be easier.
 

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whatever derailleur you want...

jakeplazma said:
Wow! I love this forum... Ask and most of the time you shall receive.

Rensho,
I tend to agree with Nino in that having your chain that short is definitely a recipe for disaster. Yes, shifting into the extreme combo's is unlikely but mistakes do happen. Why risk it? Anyay, your input is appreciated, thanks!

Nino,
I guess the total capicity figures are that conservative if it's working without any hicups. So, if using a rear der other than the DA with a total capacity of say 37T then this setup should work too, right? As always, thanks for playing!
sure, you can use whatever derailleur you like , BUT why heavier if the DA 7800 weighs just 181g and does a great job?
 

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Discussion Starter · #7 ·
nino said:
sure, you can use whatever derailleur you like , BUT why heavier if the DA 7800 weighs just 181g and does a great job?
I'm still contemplating this but leaning towards sticking with SRAM. A few reasons why: With SRAM's new X.0 rear der (short cage) it will only be ~11 grams heavier @ 192 grams. Also, the new X.0 Triggers will only be ~6 grams heavier than a tuned set of XT shifters. I know you've since lowered that mark but I really don't feel like busting out the dremel! :D So, all in all I loose roughly 17 grams but get to keep the setup i'm used to. Who knows, if there's room for tuning on the new SRAM stuff that number could very well be lowered. ;) Besides, I really do love the way the SRAM combo shifts/feels.
 

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I fully agree Nino. Not a setup for the fainthearted and inexperienced. Next time i set up a bike, I'll try the chain really loose way and see how it goes.
I will say that of either scenario, i'm more likely to shift into the 21x12 gear by mistake. I'm speaking just for myself.
 

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Discussion Starter · #9 · (Edited)
Motivated said:
I use an RD-7700-GS rear derailleur (i.e. Dura-Ace 9spd triple) for a 12-27 cassette with 42/30/20 tooth rings. The capacity is 38 teeth and I'm using 37. Only been on this for a few weeks but it is better than what I have on my trail bike: 44/32/24 x 11-32. The finer shift increments are great when cresting a hill and having the chain farther away from the ground is a bonus. In fact there is no drawback to this setup that I have detected. I do get a touch of noise in the 2 fully crossed positions gently reminding me about chain wear.

If you are contemplating this type of setup consider doing it with a 21t ring on 4-arm cranks - your ring choices and replacements may be easier.
Well, it's a good idea and will definitely work but, that would defeat one of our main purposes... which is saving weight! No savings here as that der weighs approximately the same as the long cage X.0 der.
 

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Discussion Starter · #10 ·
Motivated said:
I use an RD-7700-GS rear derailleur (i.e. Dura-Ace 9spd triple) for a 12-27 cassette with 42/30/20 tooth rings. The capacity is 38 teeth and I'm using 37. Only been on this for a few weeks but it is better than what I have on my trail bike: 44/32/24 x 11-32. The finer shift increments are great when cresting a hill and having the chain farther away from the ground is a bonus. In fact there is no drawback to this setup that I have detected. I do get a touch of noise in the 2 fully crossed positions gently reminding me about chain wear.

If you are contemplating this type of setup consider doing it with a 21t ring on 4-arm cranks - your ring choices and replacements may be easier.


^^^^^^
 

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that's true, but

Mine weighed 212g and cost $99. I don't think you can beat that weight for the same money. Plus the DA models have the nice large pulleys and the performance is historic. Besides, trust me, saving 30g on a rear derailleur at the risk of a bad shift or more drivetrain drag is not a smart choice.

The main purpose is to go faster - saving weight is a means to that end.

jakeplazma said:
Well, it's a good idea and will definitely work but, that would defeat one of our main purposes... which is saving weight! No savings here as that der weighs approximately the same as the long cage X.0 der.
 

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do a search

jakeplazma said:
C'mon, there's gotta be more of you out there riding this combo... More feedback, please!
if you need even more feedback do a search on this forum. this has been discussed on and on so i think that's the reason no more are willing to share info.

it works flawless. it's as easy.
 
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