What if you want to go lower than 27T with Shimano Ultegra?

Discussion in 'Cycling Equipment' started by sergen, Nov 30, 2005.

  1. sergen

    sergen New Member

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    My bike has full ultegra components - brakes, FD, RD, triple hollowtech chainring and a 12-15 CS6600 cassette.

    I know that Shimano's official line is to not go any lower than a 27 but recent forum users have suggested that this is just Shimano being conservative and that the rear derailleur could probably handle a 29T sprocket. Indeed, given that I never cross-chain I wouldn't have to worry about getting a new chain to cope with 52x29. I simply wouldn't use that ratio.

    But since Shimano don't manufacture a sprocket any lower than 27T, what cassettes are available on the market that would allow me to get a 30x29 gear? I'm obviously looking for something that would not cause shifting problems with Ultegra components.

    Many thanks
     
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  2. sergen

    sergen New Member

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    Sorry fot the typo error - of course, I meant to say that I currently have a 12-25 ten speed and not a 12-15!!!
     
  3. Ozark Bicycle

    Ozark Bicycle New Member

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    As suggested earlier, why not just swap the 30T inner ring for a 28T? A 28/27 is the same as a 30/29. Later, as 10 speed moves down market, Shimano will make cassettes with bigger cogs,as they abandon the "racer only" market.
     
  4. artmichalek

    artmichalek New Member

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    Biggest I know of is IRD's 12-28 cassette. But that's $119, and still not low enough. I would go with Ozark's suggestion. It's going to be a lot cheaper.
     
  5. gclark8

    gclark8 New Member

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    I have a 26 tooth TA inner chainring for a 10 speed triple, it was US$29.95 from Harris Cyclery. You want to buy it?
     
  6. sergen

    sergen New Member

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    I was under the (perhaps wrong) impression that the front derailleur could only cope with a maximum teeth differential of 22 (ie, 52 to a 30 equals 22 teeth). Swapping to a 28 tooth inner ring would be a differential of 24 and I'm sure I read somewhere (probably on this forum) that this would cause FD shifting issues.
     
  7. gclark8

    gclark8 New Member

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    It should work.

    Put the FD on the small chain ring.
    Run the RD through the range and obseve the clearance between the chain and the flat horizontal portion of the FD cage, at the back of the FD.

    Measure the clearance at the middle sprocket and the largest sprocket. This will give you an idea of how much smalller the small chain ring can be before the chain fowls the FD cage.

    The seatpost angle has an effect here as well. (Don't you just miss Mr B when you really need him?)
     
  8. Ozark Bicycle

    Ozark Bicycle New Member

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    FD "capacity" is, like RD max cog size, a very conservative spec. You can use a 28T with your FD; I've done it on several STI triples. As an aside, all STI triples require careful set-up for proper function, but a 28T works as well as 30T.
     
  9. Ozark Bicycle

    Ozark Bicycle New Member

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    Gotta disagree here: the clearance at the back of the cage is only a factor if one wants to use the inner ring with the middle and outer rear cogs. Why would you want to do that? As soon as you can have the same gear on the middle ring, it's time to get out of the inner ring. As long as the inner works with the 2 or 3 largest, innermost cogs, all is well. Those are your climbing gears. (And, BTW, if the chain does rub on the rear of the cage, the rattle is a good reminder that it's time to out of the granny ring!)
     
  10. gclark8

    gclark8 New Member

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    Lean to read!! Not the sides, the bottom/rear of the cage!!

    Ask SheldonBrown!! It is to do with the lift not the width. There is no point in fitting a small chain ring that allows the chain to drag on the bottom of the cage.
     
  11. Ozark Bicycle

    Ozark Bicycle New Member

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    I prefer to read upright! :)

    Anyway, I know what you were saying in your prevoius post and, IME, this is not wholly correct. So long as the chain will clear the bottom rear cross bar of the cage(clear enough?) on the 2 or 3 largest rear cogs, all is well. Those are your climbing gears. Why stay on the inner ring when the same gear is available on the middle ring?

    The true limitations in the minimum usable size of the inner ring are 1)FD capacity, which can usually be slightly exceeded 2) the shape of the inner cage. Shimano will usually spec a min chainring size which, again can usually be slightly exceeded. In this case, we are exceeding FD capacity and recommended min chainring size by 2T.

    Bottom line on using a 28T inner on an Ultegra Triple: it works. A 26T would be a bit dodgy on an STI road triple with a 52T outer and a 24T will probably be impossible.
     
  12. gclark8

    gclark8 New Member

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    Obviously, you have just tried this?

    Why dont you let sergen reply to the comments and not try to dominate his topic? You don't have to be right. Mr B was right in his opinion of you...

    Sergen, if you would like to e-mail me I will forward to you a 5 page PDF from Shimano on frame design and fitting front derailleurs and chainring sizing. They you can decide for yourself.
     
  13. Ozark Bicycle

    Ozark Bicycle New Member

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  14. gclark8

    gclark8 New Member

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    NO!! Left!!

    See you are not right all the time. :p
     
  15. mikeg

    mikeg New Member

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    George

    Is that 26T ring suitable for 9 speed, and have you tried it out?

    I have been considering trying a 26T granny instead of the 30T on my sirrus pro to make it easier to spin hills. current is 52/42/30

    I don't know whether you would have to change the 42 to say 40 or 39 for the shifting to work well enough.

    Mike
     
  16. gclark8

    gclark8 New Member

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    Mike,

    I have the 26 inner and 39 middle in TA, they are 10 speed, but labelled 9/10, however would need to use a 10 speed chain if you used the TA middle ring.

    You can get Sugino 9 speed chainrings from Greeenspeed, Vic. They are much cheaper than TA, also they are the Aus importers of TA. Call Mick or Rachael. I regularly buy cranksets from them. http://www.greenspeed.com.au/
     
  17. gclark8

    gclark8 New Member

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    Just for the record I checked my new bike.
    It has a 76 degree seat tube
    40mm bb drop (650c wheel)
    Triple chainring, 30/42/53 Sugino 9 speed
    Cassette 12-25 9 speed HG-50
    Front Derailleur FD-443
    Rear Derailleur RD-6500 Ultegra
    Chain HG-93 Ultegra

    With the chain on the 30 (small) I can select the 25, 23, 21 tooth sprockets, no problems, however the 19 will fowl the bottom of the derailleur cage. Using a straight edge, I estimate a 28 small will be ok on my bike, a 26 small may work on a bike with a slacker (73 degree) seat tube, it won't work on mine.

    The engineering PDFs from Shimano are all on frame design and set-up. Not the published service and parts files Richard is referring to.

    Also it would be more productive for the original poster for Richard, Ozark Bicycle Service, and I to agree not to comment on each others posts from this point in time.
     
  18. Ozark Bicycle

    Ozark Bicycle New Member

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    George,

    I'm curious, is the "new bike" you refer to your tri bike?
     
  19. gclark8

    gclark8 New Member

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    Yes, Try-Bike, not Tri-bike. Fair go, I'm over 55!! :D
     
  20. Ozark Bicycle

    Ozark Bicycle New Member

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    \

    Good one! :)

    What shifters are you using?
     
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