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  1. #1
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    Ultegra Rear Der. Design Flaw?

    I've been building up a new road bike, and was lucky to find a decent deal on an Ultegra 6600 groupset. In preparing to mount the rear derailleur, I noticed that the guide pulley had considerably more rotational friction than the lower tension pulley. The Ultegra guide pulley is a ceramic bushing system, while the tension pulley is a sealed bearing system. I decided to disassemble and relube the guide pulley, but after doing so, it really had no effect on the rotational friction. It was still much higher than the lower tension pulley.

    After thinking about the design, and comparing it to Shimano's other lines, I'm nearly certain the culprit is the friction between the metal dust caps and the rubber seals. When the guide pulley turns, the ends and sides of the dust caps rub against the rubber seals, causing rotational friction. Of Shimano's top three lines (DuraAce, Ultegra, and 105), only the Ultegra derailleur has the rubber seals on the guide pulley. My other bike, with Shimano 105 guide pulley (also bushing), has no such friction. I googled the issue, and although there is not much, there are a few forum threads where people mention the same issue. None, however, really get at the heart of the issue.

    Here's a link to Shimano's technical document on the subject, if anyone is that curious:

    http://techdocs.shimano.com/media/te...9830609120.pdf

    I don't think this issue has to do with preload vs. no preload, as there is normally not much load on the guide pulley.

    My questions are:

    Can others confirm if the higher guide pulley friction on the Ultegra is normal? Would love to hear from some professional bike mechanics, who handle alot of these things and have experience to compare their findings.

    Do the seals eventually "break in" and lessen their frictional effect?

    Would you recommend swapping out the guide pulley for one with sealed bearings? I've heard of a few people doing this and saying it worked great, eliminating the drag, but I'm wondering if there is a reason for this drag on the pulley that I'm missing.

    And, why would Shimano put a sealed bearing on the tension pulley, and a ceramic bushing on top? Why not two sealed bearing pulleys?

    I realize this might sound like an esoteric issue, but it kind of bothers me to put this kind of unnecessary drag on my drive train. Appreciate any wisdom you folks could lend to this matter.

  2. #2
    cs1
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    You're the first person who I've heard mention it. Do you really notice the difference when riding?

    Tim
    1999 Waterford RSE-11, 1995 Waterford 1200, 1989 Specialized Rockhopper Comp
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  3. #3
    30 YR Wrench BikeWise1's Avatar
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    A couple of drops of Prolink seems to free them up nicely...

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    I have Deore XT and it has the same "problem". Actually, I've been using this der for the last 500+ miles with no problems what so ever. I'm no expert but in my book I simply don't worry about this one. Hope this helps.

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    Senior Member stokessd's Avatar
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    All these new derailleurs with "sealed" pulleys have that "problem (I've got 3 XT's and a 105 with the same deal). IT's not really much of a problem, but extra drag that you don't need. I also noticed the cartridge bottom brackets also have lots more drag than older adjustable bearing bottom brackets. Progress...Bah.

    Sheldon

  6. #6
    Pwnerer Wordbiker's Avatar
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    Quote Originally Posted by AkAk2000 View Post
    My questions are:

    Can others confirm if the higher guide pulley friction on the Ultegra is normal? Would love to hear from some professional bike mechanics, who handle alot of these things and have experience to compare their findings.
    Yes, although it can be worse in certain pulleys that are further out of specs. More of a manufacturing execution issue than a design flaw.

    Quote Originally Posted by AkAk2000 View Post
    Do the seals eventually "break in" and lessen their frictional effect?
    Yes. They can also get contaminated and increase in friction. The best solution is to keep them clean and lubed as BikeWise1 described.

    Quote Originally Posted by AkAk2000 View Post
    Would you recommend swapping out the guide pulley for one with sealed bearings? I've heard of a few people doing this and saying it worked great, eliminating the drag, but I'm wondering if there is a reason for this drag on the pulley that I'm missing.
    No. Pulleys with cartridge type bearings also have inherent drag in the seals and the same issues with contamination.

    Quote Originally Posted by AkAk2000 View Post
    And, why would Shimano put a sealed bearing on the tension pulley, and a ceramic bushing on top? Why not two sealed bearing pulleys?
    There are more differences in the two pulleys than you may think. The top pulley is designed to have an engineered amount of side-to-side play. This keeps the pulley centered over the cog even if the indexing adjustment of the rear derailleur is slightly off. Shimano uses a "floating" ceramic bearing to keep tolerances for the greatest possible amount of time, yet still allow for the side play, and to compensate for their 2:1 derailleur movement/cable pull ratio. When the cable is pulled 1mm, the derailleur moves 2mm. This also means that when cables "stretch", the indexing is off by .5mm and the derailleur is off by 1mm. Point to SRAM for their 1:1 ratio.

    Replacement pulleys have been around for quite a few years now, and in my experience upon first installation, they feel more "precise". This is no doubt due to the lack of hesitation when shifting caused by a design with no side play. The precision goes away once indexing get out of adjustment and the lack of a self-centering design causes the chain to clatter on the cogs.

    The lower pulley does not need the self-centering feature and can be replaced with impunity...other than the previously mentioned fact that they too will have seals that rub and can get contaminated.

    To me it comes down to this: One can either have good, easily cleaned seals with a slight amount of drag, very well sealed bearings that are tougher to clean (or may just have to be replaced), or a lightly sealed open system that will spin freely until it gets contaminated. Shimano strikes a good balance for most users by having a design that is easily maintained, and designed to work longer with less adjusting needed.
    Last edited by Wordbiker; 07-29-07 at 12:10 PM.
    Quote Originally Posted by ahsposo View Post
    Ski, bike and wish I was gay.

  7. #7
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    Thanks for weighing in on this subject.

    You're the first person who I've heard mention it. Do you really notice the difference when riding?

    Tim
    Haven't ridden the bike yet, as I'm still building it up. I would be shocked if I do notice it on the bike. But, for that matter, in a double blind test, I'd be shocked if most cyclists could detect hub cone nuts tightened too tight, or an extra 200 grams on a bike. But, both do contribute to a diminishment of bike performance. A bike is a pretty simple machine. Any drag comes out of your own exertion. Especially when building the bike up piece by piece, why not tune each component to eliminate as much drag as possible?

    A couple of drops of Prolink seems to free them up nicely...
    I don't think it will, with all respect, unless the prolink creates a permanent slip layer between the rubber seal and the dust cap. As I mentioned, I cleaned and lubed the pulley well, using good grease. The bushing isn't providing the drag, its the friction between the rubber seal and the cap. My 105 derailleur has bushings, but no seal, and it doesn't have this drag issue.

    Yes, although it can be worse in certain pulleys that are further out of specs. More of a manufacturing execution issue than a design flaw.
    Thanks alot for your response. I found it very insightful. Are you a bike mechanic?

    Yes. They can also get contaminated and increase in friction. The best solution is to keep them clean and lubed as BikeWise1 described.

    No. Pulleys with cartridge type bearings also have inherent drag in the seals and the same issues with contamination.
    My guide pulley is near new, and well cleaned and greased. I don't think the "clean and lubed" is the issue, its the rubber seal friction.

    My cartridge bearings on the tension pulley work brilliantly. I'm sure, like you say, that they may degrade in performance as they muck up. But brand new, there's no comparison between their drag and that of the G pulley with the seal.

    To me it comes down to this: One can either have good, easily cleaned seals with a slight amount of drag, very well sealed bearings that are tougher to clean (or may just have to be replaced), or a lightly sealed open system that will spin freely until it gets contaminated. Shimano strikes a good balance for most users by having a design that is easily maintained, and designed to work longer with less adjusting needed.
    This sounds like real wisdom to me. Ultimately, it sounds like there is always some tradeoff, and Ultegra engineering seems to have gone with the tradeoff of slight dimishment of performance for lower maintenance and higher long term operating performance.

    Can you tell me if, in your experience, Dura Ace R ders, with the G pulley being sealed bearing, requires greater maintenance or replacement than the Ultegra R Der?

    Again, thanks for everyone's comments.

  8. #8
    Pwnerer Wordbiker's Avatar
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    Rather than going through the quoting thing:

    Yes, I am a mechanic, and you're quite welcome.

    The cartridge bearings I was speaking of are those found in aftermarket pulleys. They are typically sealed and pressed into an aluminum pulley. I don't know if bearing replacements are even available. When they wear out, most people buy a new pair...or go back to stock pulleys that can be maintained easier.

    In all honesty, they last about the same. Ultegra is focused at the high end of touring and enthusiast cyclists. Dura-Ace is a racing gruppo and cuts very few corners in the pursuit of performance...and still has very good durability. So much of durability has to do with maintenance, conditions of use, rider style and happenstance...meaning accidents, that ultimate durability is very tough to predict. I am admittedly much more familiar with mountain bike component groups, but you work with a few road gruppos at school and work, you get pretty familiar and they work very much the same.

    I just purchased a few drivetrain items for a TT bike, including an Ultegra rear derailleur. I'll check mine out tomorrow and let you know if it has "excessive" drag. I sure hope not. I need all the help I can get.
    Quote Originally Posted by ahsposo View Post
    Ski, bike and wish I was gay.

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