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  1. #1
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    Use of "shorter" rear derailleur



    What's up ya'll:

    I got a Gemini 1000 used awhile back and it came with the Durace (?not sure of spelling) rear der. -- the seller said that it helped keep the chain from hopping. I found out it's for road bikes.

    I need to change my drivetrain because it was build for DH, but I do aggressive XC and need the gears (the Gemini only has 8 speed and a singe ring up front) -- so I gotta couple of questions:

    1.) Are there any cons to going with a "shorter" road bike rear der. (for example, is there more friction)

    2.) If road bike rear der. stay on better than MTB der., how come that's not the standard?

    3.) Can I put a road rear der (9speed) mixed with MTB (like Shimano or SRAM) parts?

    4.) What would ya'll recommend for a drivetrain and why?

    Thanks.

    Moe

  2. #2
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    Quote Originally Posted by MoeChedda


    What's up ya'll:

    I got a Gemini 1000 used awhile back and it came with the Durace (?not sure of spelling) rear der. -- the seller said that it helped keep the chain from hopping. I found out it's for road bikes.

    I need to change my drivetrain because it was build for DH, but I do aggressive XC and need the gears (the Gemini only has 8 speed and a singe ring up front) -- so I gotta couple of questions:

    1.) Are there any cons to going with a "shorter" road bike rear der. (for example, is there more friction)

    2.) If road bike rear der. stay on better than MTB der., how come that's not the standard?

    3.) Can I put a road rear der (9speed) mixed with MTB (like Shimano or SRAM) parts?

    4.) What would ya'll recommend for a drivetrain and why?

    Thanks.

    Moe

    I can't answer everything here, But I'll answer what I know about. Dura-ace is Shimano's high end road RD, generally VERY spendy. I have no clue how it would affect the performance of a MTB. Mountain RD's generally come in short and long cage lengths, I'm running a short cage 2001 XT (mostly because I thought the shop sold me a long one and the shop wouldn't take it back). It does work very well though, and has grown on me, apparently the cage length goes to F and R gear combinations, ie the more length the more you can downshift on the rear while leaving the front in large or middle. (That's just how I understand it, I may be wrong).

    As far as mixing parts, Shimano recently changed the sping loading direction on their new RD's, so that the rest position is in the larger gear instead of the smaller as in almost all older designs. You can still use any Shimano shifter with it, but pushing with the thumb shifts up not down. On RD's SRAM uses a different cable ratio on their shifters, so a SRAM shifter must be used with a SRAM RD.

    My favorite drive-train is late 90's LX shifters, RD, and FD, 8 speed cassette/chain, sq taper BB/cranks. I like them because they don't give me much fuss and have good durability on the chain/gears. (I'm using the 2001 XT RD on my other bike, and absolutly hate chain changes at 600 miles, just my thing, not a rip on anyone, I swap the 8 speed chain at 1000 miles, and the 9 speed chain AND cassette at 1000 miles)

    I'm not certain if I understood your question or not, hope this helps.

  3. #3
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    Look at the chain capacity of the derailleur vs. the capacity you need for your gearing. If you are using a 12-34 cassette, you probably don't want to use a Dura Ace derailleur because the chain wrap capacity of the derailleur may not be enough to prevent the chain from falling off in the low gears.

    Personally I prefer 8 speed and run 11-30 cassette and 44-32-22 chainrings (prefer 34 tooth middle, but it won't work on my current setup using an e-type front derailleur). The gear spacing of this setup is about as equal as you can get and has all the range you should need for even the most technical trails.

    If I had to replace my cassette after 1,000 miles I would be very bummed! I change them annually (about 3,000 miles), but it's not like they are shot by any means.

  4. #4
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    If you...

    Quote Originally Posted by MoeChedda


    What's up ya'll:

    I got a Gemini 1000 used awhile back and it came with the Durace (?not sure of spelling) rear der. -- the seller said that it helped keep the chain from hopping. I found out it's for road bikes.

    I need to change my drivetrain because it was build for DH, but I do aggressive XC and need the gears (the Gemini only has 8 speed and a singe ring up front) -- so I gotta couple of questions:

    1.) Are there any cons to going with a "shorter" road bike rear der. (for example, is there more friction)

    2.) If road bike rear der. stay on better than MTB der., how come that's not the standard?

    3.) Can I put a road rear der (9speed) mixed with MTB (like Shimano or SRAM) parts?

    4.) What would ya'll recommend for a drivetrain and why?

    Thanks.

    Moe
    get into 30/32/34 rear cassette, you will need a long cage der. Has nothing to do with friction. As prev poster said, you need longer cage for the extra chain or it won't shift correctly in certain situations. Road bike der ARE for road bikes because biggest cog is around 22, etc. You can't mix Sram rear der with Shimano shifters, etc. Pull is different. You can use Shimano/Sram front der without any problems mixed with other components. Shimano XT is always reliable all the way through drivetrain. XTR if you can afford it, but not much improvement ove XT.

  5. #5
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    Moe: First things first, is your derailleur short cage or medium cage? On the back should be stamped a model number, such as RD-7700-SS or GS. SS=short cage, GS=medium.

    SS has a stated "Capacity" of 29T; GS has a stated capacity of 38.

    Imagine you have a 38T ring up front and an 11-32 cassette. In 38x32, you're using '0' derailleur capacity, because all of your available chain is taken up by your big ring and big cog -- your derailleur isn't "absorbing" any excess chain.

    Shift to 38x11 though, and now your chain has some slack that needs to be taken up. Subtract 11 (your small cog) from 32 (your big cog) and you come up with 21. This represents the excess chainslack your derailleur must be capable of handling while maintaining proper tension. Both the SS & GS cages lengths can handle 21T, no problem (29T & 38T respectively).

    This simple formula applies to multiple chainrings as well: Big minus Small = capacity required. So if you install a conventional 44/32/22 crankset, the formula goes:

    . (44-22) = 22 (front capacity req'd)
    +(32-11) = 21 (rear capacity req'd)
    Total req'd = 43 (meaning you would need a derailleur with 43T capacity to absorb excess chain)

    But there is a catch: this assumes you're going to be running "small-small", which is normally a unused cross-chain combo. Realistically, while in your granny ring, you'll shift only through half the range of your cassette -- to about the 20T cassette. So the formula can be modified accordingly to reflect this use, substituting the 20T cog for the 11T cog:

    . (44-22) = 22 (front capacity req'd)
    +(32-20) = 12 (rear capacity req'd)
    Total req'd = 34 (meaning you would need a derailleur with 34T capacity to absorb excess chain)

    So in reality, the 29T limit of the SS won't cut it, but the 38T capacity of the GS will!

    And the good news is Shimano tends to be a little conservative in their stated capacities.

    1.) Are there any cons to going with a "shorter" road bike rear der. (for example, is there more friction)

    No. And the benefit is the chain has less leverage over the derailleur tension spring, meaning less chain slap. Plus you get crisper shifts, and increased obstruction (i.e. rock) and spoke clearance).

    2.) If road bike rear der. stay on better than MTB der., how come that's not the standard?

    A lot of DHers have used road derailleurs on MTBs for just this reason. It's only recently Shimano has re-introduced GS to the XT lineup, although XTR has had cage length options all along.

    3.) Can I put a road rear der (9speed) mixed with MTB (like Shimano or SRAM) parts?

    With Shimano shifters, yes, but with SRAM shifters, only if they are non-ESP models such as the Attack and Rocket series.

    4.) What would ya'll recommend for a drivetrain and why?

    I'm a fan of GS cage lengths on conventional 44/32/22 & 11-34 drivetrains for all the reasons I mentioned above. The biggest among those is the increased chain control & reduced slap; the others are all bonus.

  6. #6
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    Quote Originally Posted by kenaran
    My favorite drive-train is late 90's LX shifters, RD, and FD, 8 speed cassette/chain, sq taper BB/cranks. I like them because they don't give me much fuss and have good durability on the chain/gears.
    No way! That is my ex-girlfriend's drivetrain, and it is the best thing ever! It blew my mind when I bought her Marin Rocky Ridge with that setup and it shifted better from day 1... to this day, too, than any xtr or sram setup I've had (and I know how to set shiyat up, yeah, boy).

    She's not mechanically inclined, and I'm glad the drivetrain is bulletproof and slick cuz now that I'm the ex, the current GF wouldn't take too kind if I was going over and working the other girl's stuff, know what I mean?

    Seriously, late 90s LX was great!

  7. #7
    Mantis, Paramount, Campy
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    Dura Ace not very expensive

    Quote Originally Posted by kenaran
    I can't answer everything here, But I'll answer what I know about. Dura-ace is Shimano's high end road RD, generally VERY spendy. I have no clue how it would affect the performance of a MTB. Mountain RD's generally come in short and long cage lengths, I'm running a short cage 2001 XT (mostly because I thought the shop sold me a long one and the shop wouldn't take it back).
    Acually the Dura-Ace rear derailleur is probably the best value in all of cycling. Its about half the price of XTR with better performance and weighs about an ounce less.

    Also, with the exception of XTR mountain derailleurs havent been available with a short cage(ss) in many years. You probably have a mid-cage model (gs)

  8. #8
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    use caution with short cage and short chain

    With the single pivot of your Gemini, you need to be careful with your chain length selection. Your chain will tighten up significantly when you're close to bottoming out the suspension. What I do ( I run 22/32bashguard) is shift to big gear (34) and 32 chainring. Then install the new chain and select a length that keeps the jockey gears straight up/down (perpendicular to the ground). This gives me enough play in the derailleur tension to prevent snapping it off on big hits. BTW, I use an Ultegra double rear derailleur for my San Andreas. Very cheap and lite!
    No dabs allowed!

  9. #9
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    Half the price??

    Its about half the price of XTR...

    Where did you see a Dura Ace deraileur for half the price of an XTR? I'd pick up a spare at those prices...

    2004 Dura Ace RD-7800 $125.93
    2004 XTR-M960 $130.43

  10. #10
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    Anywhere

    Before DA went 10 speed (2003, 2002,....) the price was $69 or mid-cage for $79 at any online shop. I wasn't aware of the price increases. The last time I bought a new derailleur was about 6 years ago.
    Last edited by Shayne; 12-09-2004 at 03:22 PM.
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  11. #11
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    You mean Ultegra..

    Quote Originally Posted by Shayne
    Before DA went 10 speed (2003, 2002,....) the price was $69 or mid-cage for $79 at any online shop. I wasn't aware of the price increases. The last time I bought a new derailleur was about 6 years ago.
    DA went 10sp in '04. Dura Ace stuff has always been similarly priced to XTR. The old model RD-7700 still fetches $70.00 to $100.00 on ebay, USED, Obsolete (Dura Ace is now 10sp) and over a year old.. That's more than what '03 XTR derailleurs get on ebay.

    example.. http://search-completed.ebay.com/dur...1QQsotrvalueZ1

    I bought mine about two years ago for well over $100.00 from Jensonusa.com. I shopped them all before I made my purchase. Jensonusa, pricepoint, beyondbikes, speedgoat, adrenalinebikes, mtbstore, cambriabike. To name a few. mtbstore and cambriabike still have a few left from last year. Both sites still sell them for over $119.00....

    Anyway, I run a DA rear derailleur because the short cage works better with my single 36t chainring. I also use the 12-27 DA cassette as I rarely (never) used the 34t bailout gear when I had it.. 36-27 get's me up just about anything.
    Last edited by GGAllen; 12-10-2004 at 11:46 PM.

  12. #12
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    No, I meant Dura Ace

    I hold in my hand a 2003 Cambria and a 2003 Colorado Cyclist that have the DA derailleur for $69 and Ultegra for $47....not on sale, regular prices. I have never seen a short cage Ultegra for more than $50, again the move to 10 speed excluded.

    Dura Ace f and r derailleurs have been far cheaper than XTR from its introduction.
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  13. #13
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    Now I know your blowin' smoke..respectfully

    Dura Ace f and r derailleurs have been far cheaper than XTR from its introduction.
    Directly from www.cambriabike.com ..... Feel free to look yourself. Or on ANY website for that matter. Mind you I have seen other sites where the price fluctuates a few dollars in either direction.

    This is far cheaper??

    Dura Ace shifters $430.95
    XTR shifters $399.95

    DA cranks $479.95
    XTR cranks $457.95

    DA Cassette (9sp) $128.95
    XTR Cassette $133.95

    DA fr derailleur $91.95 --> 6.1% = far cheaper?
    XTR fr derailleur $97.95

    DA rr derailleur $128.95 --> 3.7% = far cheaper?
    XTR rr derailleur $133.95

    Look, I don't want someone to sell there current derailleur thinking they can get a Dura Ace one "far cheaper" or "half the price" because it isn't going to happen. I'm in no position to debate the price of something years ago (as you're the only one with the "proof").

    I'm saying today, right now, you can't purchace a Dura Ace derailleur for anywhere near half of an XTR. New OR used.

    Please feel free to challenge this and post a website showing cheap DA stuff. I'm always looking for a deal.

    I have never seen a short cage Ultegra for more than $50
    Here is one of many online sites blowing out Ultegra 9sp derailleurs. For $65.00 ---> http://www.beyondbikes.com/BB/ItemDe...2DDER%2Drd6500
    Last edited by GGAllen; 12-11-2004 at 01:21 PM.

  14. #14
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    Fair Enough

    But for the third time I am talking pre-10 spd Dura Ace. I was unaware that they doubled the prices of their derailleurs.

    Here are prices directly from my '03 Cambria Catalogue.

    XTR $95....DA $69.....Ultegra $45
    Comperable DA was 28% less

    XTR fd $79....DA fd $42
    DA was 47% less

    I consider 28% a notable savings.

    Clearly with 10spd, Dura Ace is no longer the best value in cycling components.
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  15. #15
    Meh.
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    A lot of guys use roadie derailleurs for their DH rigs. Shorter cage, so it is less likely to smack stuff. It also provides crisper shifts. Also has to do with chain tension. As for using a roadie derailleur with a MTB cassette, it probably won't work, because road derailleurs use much smaller cassettes (in the sense of the number of teeth, not spacing). However, using roadie derailleurs with MTB chains and shifters shouldn't make a difference. If you're going 9 speed, don't forget to get the 9 speed chain, since they are much narrower than the 8 speed chains. As for why not all MTB are using short cage derailleurs? SRAM is incorporating the Shimano Blackbox carbon fiber technology into a new x.0 rear derailleur for DH applications. It has a short cage measuring 55 millimeter pulley to pulley.

  16. #16
    Meh.
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    Quote Originally Posted by XSL_WiLL
    SRAM is incorporating the Shimano Blackbox carbon fiber technology into a new x.0 rear derailleur for DH applications.
    Whoops, I meant the Rockshox blackbox carbon technology. Same as the crowns on the SID forks. Not sure what I was thinking.

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