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  1. #1
    Part-time epistemologist invisiblehand's Avatar
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    road derailer with 32 cog cassette

    Hi,

    I did several searches and needed to wrap up a few questions regarding putting a MTB-wide cassette onto a road bike with a road-triple rear derailer.

    From what I understand, whether on can fit a cassette with a 32-tooth cog depends on whether the jockey pulley clears the big cog. The tension pulley simply determines whether the derailer can pull enough chain such that all combinations can be reached in the derailer drivetrain.

    I have a 12-32 speed cassette on an older bike. Would putting on the old cassette and seeing whether I could adjust the b-screw enough to clear the cog be a sufficient test for whether a wide (12-32) 10-speed cassette would work? I think yes.

    Thanks for reading and any advice.

    Just in case anyone is wondering, I am switching from a triple crank to a compact crank. So I have an Ultegra long cage (GS) rear derailer.

    A particularly appropriate old thread ...

    Would This Derailleur/Cassette Combination Work?

    EDIT: Just to be clear, I would not actually run a chain around the 7-speed cassette. I would simply move the cassette as far inward as possible and begin adjusting the b-screw.
    Last edited by invisiblehand; 01-28-09 at 06:58 PM.

  2. #2
    Senior Member Retro Grouch's Avatar
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    I'm always for experimenting with parts that you already own. If it was my bike I'd test fit the cassette and see if I could get the existing derailleur to work. My guess is that you're pushing the limits of the road derailleur but if it works that would be cool.

    A trick that you might try is to completely remove the b screw and reinstall it from the other side. That will give you another couple of millimeters of effective length.

  3. #3
    DRF aka Thrifty Bill wrk101's Avatar
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    I plan to switch my Ultegra double with a compact myself. And then probably a wider range cassette. So I will be interested in how this works for you.

    +1 Since you have the parts on hand, its a no cost test. I would make the swap, try it out on a couple of short local rides. I wouldn't want to be in the middle of a longer ride, away from tools, home, etc., and have a problem. Best to test ideas out locally. So if you have to walk home, no big deal.

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    Can you get a 32T cassette in 10 speed? I thought mtb stuff was 9 speed.

  5. #5
    Part-time epistemologist invisiblehand's Avatar
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    Quote Originally Posted by shelbyfv View Post
    Can you get a 32T cassette in 10 speed? I thought mtb stuff was 9 speed.
    yep ... IRD imports them to the US.

    http://www.interlocracing.com/index.html

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    Great State of Varmint Panthers007's Avatar
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    I like the IRD stuff I've seen so far. Very good quality.
    How do you keep an idiot in suspense?

  7. #7
    Part-time epistemologist invisiblehand's Avatar
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    So I just put the bike on the stand and took some measurements. Essentially I tightened the b-screw all the way and took a rough measurement of the vertical distance between the jockey pulley and the 27t cog. I measured ~3/4".

    Some quick calculations ...

    circumference = pi * d
    ( teeth * 1/2") / pi = d

    ergo ...

    5 / (2 * pi) " = the change in diameter

    roughly this will be 4/5" so the change in the radius will be ~2/5". I think that it will work. Will it work well? We will have to see.

    Placing the order for the cassette now!

    EDIT: Since someone else is thinking of doing the same thing, I have a Salsa La Raza 56 cm frameset. As you may already know, it has a very traditional geometry. So if you have a similar bike, my measurements might help you.

  8. #8
    Gear Combo Guru Chris_W's Avatar
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    Quote Originally Posted by invisiblehand View Post
    ... Essentially I tightened the b-screw all the way and took a rough measurement of the vertical distance between the jockey pulley and the 27t cog. I measured ~3/4". ...
    If this is still not enough, then I've read that you can take the b-screw all the way out, and the derailleur off of the bike, and then screw the b-screw in from the back side of it's normal hole. Only screw it in enough that the threads are all engaged. When you put the derailleur back on the bike, the screw head will be the thing that contacts the stop on the frame. This effectively makes the screw a few mm longer, which might give you the extra that you need.

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    The downside of extending the b-screw travel is that the jockey pulley will be further from the smaller cogs than ideal so shifting at the high end of the cassette can be compromised.

  10. #10
    Part-time epistemologist invisiblehand's Avatar
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    Quote Originally Posted by Chris_W View Post
    If this is still not enough, then I've read that you can take the b-screw all the way out, and the derailleur off of the bike, and then screw the b-screw in from the back side of it's normal hole. Only screw it in enough that the threads are all engaged. When you put the derailleur back on the bike, the screw head will be the thing that contacts the stop on the frame. This effectively makes the screw a few mm longer, which might give you the extra that you need.
    I saw Sheldon Brown's page -- it is on his website, but Tom Deakins might have written it -- on the topic and they mention the trick. Personally, I would just stop by the hardware store and get a longer screw. It would make adjustments much easier.

    Quote Originally Posted by HillRider View Post
    The downside of extending the b-screw travel is that the jockey pulley will be further from the smaller cogs than ideal so shifting at the high end of the cassette can be compromised.
    After I tightened the b-screw I shifted through the cassette. I did not notice anything detrimental. However, there might be some effect when shifting under a heavy load.

  11. #11
    Part-time epistemologist invisiblehand's Avatar
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    Update ...

    Cassette came in the mail today. Setup was as easy as pie. I'll take some pictures later and post them here. I would have posted pictures today but I was in a rush and stripped a few threads on my crank ...

    But the story ends well and I eventually got the crank off.


  12. #12
    Senior Member Deanster04's Avatar
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    Any long cage RD will work. I helped a friend get a 11-32t cassette mounted on his road wheel using an older 105 group LC RD. I didn't know that Ultegra made a LC RD (90mm spacing). The only Ultegra RD I have seen were medium cage (75mm spacing). That is why the XT RD is recommended for using with the MTB cassette. My friend just happened to have an old 105 LC RD so we used that one. Take out a mm tape and measure the distance between the jockey wheel spacing center to center to determine the cage type.

    I have a touring wheel that I have an 11-34t cassette and Shimano type hub body (after market) on a campy Centaur hub and am using a Centaur LC RD with 10spd campy Ergos. Works fine. The campy 10spd and shimano 9spd cassettes have relatively close spacing and work well together.

  13. #13
    meb
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    Senior Member meb's Avatar
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    Quote Originally Posted by invisiblehand View Post
    Hi,

    I did several searches and needed to wrap up a few questions regarding putting a MTB-wide cassette onto a road bike with a road-triple rear derailer.

    From what I understand, whether on can fit a cassette with a 32-tooth cog depends on whether the jockey pulley clears the big cog. The tension pulley simply determines whether the derailer can pull enough chain such that all combinations can be reached in the derailer drivetrain.

    I have a 12-32 speed cassette on an older bike. Would putting on the old cassette and seeing whether I could adjust the b-screw enough to clear the cog be a sufficient test for whether a wide (12-32) 10-speed cassette would work? I think yes.

    Thanks for reading and any advice.

    Just in case anyone is wondering, I am switching from a triple crank to a compact crank. So I have an Ultegra long cage (GS) rear derailer.

    A particularly appropriate old thread ...

    Would This Derailleur/Cassette Combination Work?

    EDIT: Just to be clear, I would not actually run a chain around the 7-speed cassette. I would simply move the cassette as far inward as possible and begin adjusting the b-screw.
    Was contemplating a similar change from a 27T to a 32T on a GT road bike, Sora Rder.
    I've got a couple of bikes that have Suntour 14-32 5 cog freewheels on them I was going to use for sizing.
    Biggest concern I have is the 14-32s are on 120mm droppout wheels and I'm wanting to test it on an Al GT bike with 130 mm dropouts, so I can't tighten the wheel on with the existing spacers, and am not sure if there will be enough axle to test if I put spacers for a 130mm droppout on the axle in place. Also, I MAY not be able to test the 14-32 on that bike with tires inflated due to chainstay clearance anyway as the GT road bike has a 700-23 and the true 14-32 on the Raleigh Super Grand Prix is bearing a 700-35 and the untrue 14-32 from the Schwinn Super Sport is a 27x 1 1/8.

    Any thoughts on how meaningful the sizing test will be if I can't tighten this down and ride it on an inflated tire?

    I do have a road wheel with 126mm dropout spacing on a Raleigh Technium, but the Technium has a 4 prong 13-28 Suntour mounted and won't fit my 2 prong puller like the 14-32 Suntours mentioned above do.
    As I have 3 wheels mounted with 4 prong Suntours and a couple of 4 prong unmounted 14-38s, I probably should get that puller, and if I do will I have enough axle to add spacers to get to 130mm and try the test?

  14. #14
    Part-time epistemologist invisiblehand's Avatar
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  15. #15
    Part-time epistemologist invisiblehand's Avatar
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    Quote Originally Posted by meb View Post
    Any thoughts on how meaningful the sizing test will be if I can't tighten this down and ride it on an inflated tire?
    I think that there are two issues. One, you can't ensure that the big cog is in the correct lateral location for your derailer built for 130 mm -- eight/nine speed -- spacing. I guess you could take some careful measurements and place spacers to put the big cog in that location. But it sounds like a lot of work to me. Two, the width of the freewheel is different than a nine-speed cassette. At least I recall that it is. So the test of how the shifting performs over the entire range probably would be poor.

    I would ask around to find a bud with a MTB with a 12-32 cassette and trade him a beer for 30 minutes with his cassette.

    Alternatively, you could simply use my calculation and adjust the b-screw to see how much distance you can get. In my case, it was obvious the the jockey pulley could be adjusted enough to fit the cog.
    Last edited by invisiblehand; 02-17-09 at 09:35 AM.

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