Rear derailleur compatibility across 9,10 and 11 speeds
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  1. #1
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    Rear derailleur compatibility across 9,10 and 11 speeds

    This is a question that’s been on the back burner for a while now. Thought this would be the perfect time to lay it out here.
    1. Rear derailleur works by the pulley moving across the width of the cassette. The cable pull is regulated by the amount of cable pull within the shifter mechanism. What’s stopping me from using a older model 8 speed derailleur with a 11 speed shifter? Or a 9 speed? The cassette hub is a constant fixed width. The only variable is the spacer width and the cog thickness. Theoretically, setting the high and low limits should take care of that. Let’s have the yay’s and nay’s on why it should or shouldn’t work.


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    Been asked about a bazillion times. 100% Nay won't work. The pull ratios are different.
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    8, 9, and 10 are the same cable pull ratio...except for 4700. It's 10 speed but the cable pull is the same as 6800/8000 and 9000/9100. You can use the 8 speed derailleur w/ any 8 or 9 speed shifter, and all 10 speed shifters except 4700 Tiagra. It won't work w/ ANY 11 speed shifter. You can use the 8 speed derailleur w/ any 8 or 9 speed mtb shifter as well, but no 10 speed (Dyna-Sys) shifter will work.
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    Quote Originally Posted by arshak View Post
    This is a question that’s been on the back burner for a while now. Thought this would be the perfect time to lay it out here.
    1. Rear derailleur works by the pulley moving across the width of the cassette. The cable pull is regulated by the amount of cable pull within the shifter mechanism. What’s stopping me from using a older model 8 speed derailleur with a 11 speed shifter? Or a 9 speed? The cassette hub is a constant fixed width. The only variable is the spacer width and the cog thickness. Theoretically, setting the high and low limits should take care of that. Let’s have the yay’s and nay’s on why it should or shouldn’t work.
    As others have noted, as long as the cable pull is consistent then it will work. But when you say "older" derailleur, you might find that a newer 8s derailleur will work better than an older 8s derailleur just because there are improvements in derailleurs over time. Might not be an issue in your specific application.

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    So, how exactly are you going to get to 9,10, & 11 speed gears? ... when the shifters only go to ...8?
    I think you're going to be missing some gears!
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    Quote Originally Posted by duriel View Post
    So, how exactly are you going to get to 9,10, & 11 speed gears? ... when the shifters only go to ...8?
    I think you're going to be missing some gears!
    Reading comprehension issues or trolling? The OP said "8 speed derailleur with a 11 speed shifter"

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    OK, I got it backwards. I guess I got mixed up with another thread about/with a 11 spd hub/wheel.
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    Quote Originally Posted by cxwrench View Post
    8, 9, and 10 are the same cable pull ratio...except for 4700. It's 10 speed but the cable pull is the same as 6800/8000 and 9000/9100. You can use the 8 speed derailleur w/ any 8 or 9 speed shifter, and all 10 speed shifters except 4700 Tiagra. It won't work w/ ANY 11 speed shifter. You can use the 8 speed derailleur w/ any 8 or 9 speed mtb shifter as well, but no 10 speed (Dyna-Sys) shifter will work.
    Exactly this. Shimano changed the cable pull ratio on 11-speed road and 10-speed mountain to pull more cable.

    Unless this 8-speed rear derailleur is one you have lying around your bike parts pile, why would you want to buy an 8-speed one when 11-speed rear derailleurs are relatively cheap anyway?
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  9. #9
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    Quote Originally Posted by duriel View Post
    So, how exactly are you going to get to 9,10, & 11 speed gears? ... when the shifters only go to ...8?
    I think you're going to be missing some gears!
    I think you misunderstood me. The shifters will be the change in the constant. If I use 11 speed shifters with 8 speed Dura Ace rear derailleur, the cable pull will be regulated by the shifters themselves. If the hub width remains a constant as well, wouldn’t the 8spd rear derailleur work just as well?


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    Quote Originally Posted by Lombard View Post
    Exactly this. Shimano changed the cable pull ratio on 11-speed road and 10-speed mountain to pull more cable.

    Unless this 8-speed rear derailleur is one you have lying around your bike parts pile, why would you want to buy an 8-speed one when 11-speed rear derailleurs are relatively cheap anyway?
    Lockdown blues and boredom. I have an old DA 8 speed derailleur in the spare parts bin. Will update if my theory holds or not as the case maybe.


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    Quote Originally Posted by arshak View Post
    I think you misunderstood me. The shifters will be the change in the constant. If I use 11 speed shifters with 8 speed Dura Ace rear derailleur, the cable pull will be regulated by the shifters themselves. If the hub width remains a constant as well, wouldn’t the 8spd rear derailleur work just as well?
    No, an 11 speed road shifter has a different pull ratio than an 8, 9 or 10 speed. Any 8, 9 or 10 speed road shifter will work with any 8, 9 or 10 speed road rear derailleur (unless it's Tiagra 4700). However, the 11 speed road system pulls more cable per shift and therefore is not backwards compatible.

    I'm still not sure what you are trying to do here. What do you have on your bike as far as shifters, rear derailleur and cassette and what is it you are trying to change?
    Last edited by Lombard; 08-12-2020 at 06:02 PM.
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  12. #12
    'brifter' is f'ing stupid
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    Quote Originally Posted by arshak View Post
    I think you misunderstood me. The shifters will be the change in the constant. If I use 11 speed shifters with 8 speed Dura Ace rear derailleur, the cable pull will be regulated by the shifters themselves. If the hub width remains a constant as well, wouldn’t the 8spd rear derailleur work just as well?


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    Nope. The cable pull is regulated by the shifter but not how much the derailleur moves. That's a combination of cable pull and derailleur geometry.
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    Quote Originally Posted by Lombard View Post
    No, an 11 speed road shifter has a different pull ratio than an 8, 9 or 10 speed. Any 8, 9 or 10 speed road shifter will work with any 8, 9 or 10 speed road rear derailleur (unless it's Tiagra 4700). However, the 11 speed road system pulls more cable per shift and therefore is not backwards compatible.

    I'm still not sure what you are trying to do here. What do you have on your bike as far as shifters, rear derailleur and cassette and what is it you are trying to change?
    Like I said, lockdown boredom and the fact that I have an old 8 speed kicking around. Believe it or not I have managed to get a 10 speed Rival derailleur work with a 9 speed cassette with help from 9 speed Campy Daytona. I will keep you updated on this thread as to where the boredom driven rabbit hole leads me. ‘Tis curiouser & curiouser said the bunny wabbit


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    Quote Originally Posted by arshak View Post
    Like I said, lockdown boredom and the fact that I have an old 8 speed kicking around. Believe it or not I have managed to get a 10 speed Rival derailleur work with a 9 speed cassette with help from 9 speed Campy Daytona. I will keep you updated on this thread as to where the boredom driven rabbit hole leads me. ‘Tis curiouser & curiouser said the bunny wabbit.
    Haha! OK. Not sure about SRAM compatibilities. I'd have to look that up. CXWrench would know for sure. But hey, if you're bored, try 'em all, LOL!
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  15. #15
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    Quote Originally Posted by Lombard View Post
    No, an 11 speed road shifter has a different pull ratio than an 8, 9 or 10 speed. Any 8, 9 or 10 speed road shifter will work with any 8, 9 or 10 speed road rear derailleur (unless it's Tiagra 4700). However, the 11 speed road system pulls more cable per shift and therefore is not backwards compatible.
    If that's true then theoretically an 8 speed der will over shift because it was designed to move further with less cable being pulled.

    Try it to find out. "more" cable being pulled doesn't necessarily mean it's not still be 'close enough', It won't be perfect but wouldn't shock me if it worked acceptably.

  16. #16
    xxl
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    Quote Originally Posted by cxwrench View Post
    Nope. The cable pull is regulated by the shifter but not how much the derailleur moves. That's a combination of cable pull and derailleur geometry.
    Yep. Metaphorically, the derailleur is the big dumb boyfriend doing all the heavy lifting while the shifter is the cute girlfriend calling the shots and telling him where she wants the furniture placed.
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    Quote Originally Posted by Jay Strongbow View Post
    If that's true then theoretically an 8 speed der will over shift because it was designed to move further with less cable being pulled.
    Yep.

    Quote Originally Posted by xxl View Post
    Yep. Metaphorically, the derailleur is the big dumb boyfriend doing all the heavy lifting while the shifter is the cute girlfriend calling the shots and telling him where she wants the furniture placed.
    Hahah! Good analogy!
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    Quote Originally Posted by xxl View Post
    Yep. Metaphorically, the derailleur is the big dumb boyfriend doing all the heavy lifting while the shifter is the cute girlfriend calling the shots and telling him where she wants the furniture placed.
    Kind of the opposite in this situation. Instructions on placing the furniture are a given.
    The cable pull from the shifters is what it is no matter what. Different ders make different decisions on placing the furniture with the same instructions.

  19. #19
    xxl
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    Quote Originally Posted by Jay Strongbow View Post
    Kind of the opposite in this situation. Instructions on placing the furniture are a given.
    The cable pull from the shifters is what it is no matter what. Different ders make different decisions on placing the furniture with the same instructions.
    I think we're on the same page: The "instructions" are coming from the shifter-dictated cable pull/girlfriend, and the actual shifts of chain are being performed by the derailleur/boyfriend, yes?

    [Of course, IRL, the actual girlfriend is continually updating those instructions as to where the furniture is to be placed, sometimes in boyfriend's mid-lift, so the metaphor isn't perfect. ]
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    Rear derailleur compatibility across 9,10 and 11 speeds

    Quote Originally Posted by Lombard View Post
    Haha! OK. Not sure about SRAM compatibilities. I'd have to look that up. CXWrench would know for sure. But hey, if you're bored, try 'em all, LOL!
    Update: I am going over the deep end because of lockdown related nuttiness. I have decided to mess around with my 29er first. Now, I know there are going to be a lot of indignation that I am introducing a (gasp) mtb onto a road bike forum but hear me out. This is a investigatory phase 1.
    I am going to replace my well designed and tested Shimano XT/XTR components with Chinese components from Sensah.
    Currently, I have 2x setup. I am jumping to 1x and 11 speed. Got the cassette, chain and brake set. Waiting on the shifters. Will update after install and provide feedback. Besides,it can’t be any worse than SRAM.


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    Quote Originally Posted by arshak View Post
    Update: I am going over the deep end because of lockdown related nuttiness. I have decided to mess around with my 29er first. Now, I know there are going to be a lot of indignation that I am introducing a (gasp) mtb onto a road bike forum but hear me out. This is a investigatory phase 1.
    I am going to replace my well designed and tested Shimano XT/XTR components with Chinese components from Sensah.
    Currently, I have 2x setup. I am jumping to 1x and 11 speed. Got the cassette, chain and brake set. Waiting on the shifters. Will update after install and provide feedback. Besides,it can’t be any worse than SRAM.
    What is so bad about SRAM? Their mountain components are excellent and their road components have drastically improved since they started with road stuff.

    Man, if you are really that bored, why don't you just ride your bike more as in until you are so tired you're not thinking about beimg bored anymore? It's much cheaper.
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  22. #22
    'brifter' is f'ing stupid
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    Quote Originally Posted by arshak View Post
    Update: I am going over the deep end because of lockdown related nuttiness. I have decided to mess around with my 29er first. Now, I know there are going to be a lot of indignation that I am introducing a (gasp) mtb onto a road bike forum but hear me out. This is a investigatory phase 1.
    I am going to replace my well designed and tested Shimano XT/XTR components with Chinese components from Sensah.
    Currently, I have 2x setup. I am jumping to 1x and 11 speed. Got the cassette, chain and brake set. Waiting on the shifters. Will update after install and provide feedback. Besides,it can’t be any worse than SRAM.


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    You don't have a clue about SRAM for one thing...and you need to just go ride your bike for another. But since you're going to do it anyway I am interested to see how the Chinese stuff works. And further down the road how it holds up.
    #promechaniclife

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    Quote Originally Posted by Lombard View Post
    What is so bad about SRAM? Their mountain components are excellent and their road components have drastically improved since they started with road stuff.

    Man, if you are really that bored, why don't you just ride your bike more as in until you are so tired you're not thinking about beimg bored anymore? It's much cheaper.
    You are right as to riding my bike which I am doing at dawn for a couple of hours. The bikes components upgrade or downgrade as the case maybe just to satisfy my itch to tinker with my bike(s). I am curious as to how the Chinese stuff works. As to SRAM, I don’t like the way they work or sound when you shift. Almost like something broke.


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    Doesn't an 7 & 8 speed Dura Ace rear derailleur have a different geometry than everything else, that is 8,9, or 10?????

    "1997 was a very big year for Dura-Ace. The system went to 9 speeds, and that was the most publicized change. In addition, however, the entire Dura-Ace system was redesigned and made to be inter-compatible with other Shimano components."

    "The major difference between pre-1997 Dura-Ace and the rest of the Shimano lines is the cable travel of the rear derailer. Old Dura-Ace used a shorter amount of cable travel per shift. This has to do with the geometry of the cable attachment. Since the cable moved a shorter distance per shift, effects of cable friction or inaccurate cable adjustment were magnified.

    With the introduction of the 6-speed 600EX S.I.S. group, the cable attachment on the rear derailer changed, so that the cable had to move farther per shift. This change reduced cable tension, reduced the effects of cable misadjustment and friction, and generally made for a more forgiving system. The same geometry was adapted for 9-speed Dura-Ace when it was introduced in 1997. All subsequent S.I.S. groups match the travel of the 600EX, except the 10-speed "Shadow" XTR derailers and shifters, which have an even longer cable travel.."
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  25. #25
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    Quote Originally Posted by arshak View Post
    You are right as to riding my bike which I am doing at dawn for a couple of hours. The bikes components upgrade or downgrade as the case maybe just to satisfy my itch to tinker with my bike(s). I am curious as to how the Chinese stuff works. As to SRAM, I don’t like the way they work or sound when you shift. Almost like something broke.
    Didn't curiosity kill the cat?

    Interesting your take on SRAM. It does have a more defined click compared to Shimano's what has been described as an SBD fart smooth transition.

    I'd be leery about how the Chinese drivetrain holds up, but hey, unlike a bike frame which can fail catastrophically, if it fails, the worst that would happen is that you may one day be limping home on a 2-speed. Depending on the number and grade of the hills on that 2-speed ride, I doubt you will be bored.
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