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Thread: cassette change

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    cassette change

    I have a Shimano 105 rear derailleur with a SRAM 12-26 cassette and triple crank. that I want to change. I have been out of cycling for a while and need alittle extra help with the hills until I get my legs back. What is the max size cassette i can use with the 105 Derailleur? I have been told 11-28 or 12-30. Any mechanics out there that can set me straight? Thanks.

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    105 Long cage or short?
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    Ah, good question. I'm not sure and the bike is at home.

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    semifreddo amartuerer 'nother's Avatar
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    Quote Originally Posted by operator
    105 Long cage or short?
    Cage length doesn't matter. If he's got a triple, he's almost certainly got long cage. Cage length does not determine cog capacity.

    With 105 (or any other Shimano "road" RD), you might be able to get a 30T on there; depends on your frame. Try it. You'll have to adjust the B-tension screw to prevent the upper pulley wheel from rubbing on the largest cog -- if you can't adjust it far enough away, it'll rub the cog and the chain, causing premature wear on the drivetrain. But you can pick up a "mountain" RD (long cage, for triple, not because of the larger cog size) for relatively cheap. Look for Deore-level (that's roughly 105 equivalent).
    Last edited by 'nother; 06-13-06 at 09:37 AM.
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    What size are your chainrings? A typical 105 triple will have 52-42-30 chainrings. As an alternative you could possibly replace the granny chainring with something a bit smaller like a 28. Larger cogs will add weight, a smaller chainring will reduce weight.

    Al

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    Thats a thought as well. My triple is the standard 30-42-52. I've seen chainrings as small as 22T. That might be a better choice than a new cassette. Thanks!

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    Mad bike riding scientist cyccommute's Avatar
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    Quote Originally Posted by rick.seattle
    Thats a thought as well. My triple is the standard 30-42-52. I've seen chainrings as small as 22T. That might be a better choice than a new cassette. Thanks!
    With the 105 you will probably be limited to a 24. The bolt circle diameter (BCD) of a 22 is much smaller.
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    Quote Originally Posted by rick.seattle
    Thats a thought as well. My triple is the standard 30-42-52. I've seen chainrings as small as 22T. That might be a better choice than a new cassette. Thanks!
    Increasing the difference between the granny and middle ring sizes may reduce shifting performance. If you can get the job done with a 28 that's what I'd try, or maybe a 26 or a 27. The shift from the granny to the middle is tricky enough from 30 to 42.
    And yes you must have the correct BCD, 74mm.

    Al

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    I wasn't hinking of going to the 22T i just had seen them that small.
    I just need a little extra help up the steeper hills so a 28 might work great.
    What would the difference be between a new 28T chainring and a 12-28T Cassette?

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    Quote Originally Posted by rick.seattle
    I wasn't hinking of going to the 22T i just had seen them that small.
    I just need a little extra help up the steeper hills so a 28 might work great.
    What would the difference be between a new 28T chainring and a 12-28T Cassette?
    Lowest gear now: 30/26 X 27 = 31.15 gear inches
    28 rear cog 30/28 X 27 = 28.93
    28 front ring 28/26 X 27 = 29.08

    Changing the granny chainring to a 28 and leaving the cassette at 12-26 is almost the same as changing the cassette to a 12-28 or something with a 28. Either way you'd get about a 7% lower gear.
    If you need a bigger change you could try a 26 granny ring which will result in 27 gear inches.

    Al
    Last edited by Al1943; 06-13-06 at 02:57 PM.

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    semifreddo amartuerer 'nother's Avatar
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    Generally a 2 tooth difference on the front will not matter as much as a 2 tooth difference on the rear, but in this case it comes out pretty close, slightly favoring a new 28T cassette:

    current: 30 x 26 = 30.4 gear inches
    proposed new chainring: 28 x 26 = 28.4 gear inches
    proposed new cassette: 30 x 28 = 28.3 gear inches
    both new: 28 x 28 = 26.4 gear inches

    In any case, it's not *really* that much of a difference, even with both new cassette + chainring.

    See http://sheldonbrown.com/gears/ to play with other ideas.
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    Thanks to all for your help!
    I'm heading to the shop...we'll see what I come out with!

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    Mad bike riding scientist cyccommute's Avatar
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    Quote Originally Posted by rick.seattle
    Thanks to all for your help!
    I'm heading to the shop...we'll see what I come out with!
    As 'nother said go over to Sheldon Brown's gear calculator and play around. If you want to do something really crazy, try going with a mountain bike crank (44/34/22) and an 11-28 (Sheldon calls it a 'High and wide") cassette. You lose some on the top (105" vs 115") but you get down to a 20" gear on the low end. Considering that a 100" gear used to be standard and that most of us, even in very hilly terrain, don't really use a 115" gear that often, the 105" gear is pretty good. The other benefit you gain is that a 44/34/22 uses a pretty short chain and the shifts are nice and crisp. I have this on my touring bike which I use for general riding too and never miss the really high top gear...and I'm a speed freak

    If you go to a 46/34/22 or a 46/36/22 crank, you keep the same high gear but you still get the benefit of the small crankset.
    Last edited by cyccommute; 06-13-06 at 03:04 PM.
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    Hey Rick, where are you in Seattle?

    I have a 26 chain ring that I bought for my 105 Triple but never installed. I live near Alki and work 1/2 a block from Gregg's Greenlake. If it's easy to hook up, you can have the thing free. Better than going unused in a box in my garage. You just might need a set of washers/spacers but they're cheap.

    PM me and let me know if you're interested.

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    I like the idea of changing the chainring. That way you keep the tighter cassette and you get the lower range that you need.

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    I have successfully use an 11X32 cassett on both a 105 tripple and the Ultegra tripple. You will need a longer chain and adjust the B screw so the jocky wheels will clear the gears. This latter adjustment is one of the limiting factors in size of the gear.

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    Quote Originally Posted by cyccommute
    If you go to a 46/34/22 or a 46/36/22 crank, you keep the same high gear but you still get the benefit of the small crankset.
    Going to a chainring set this small is not possible or at least not practical on some frames with braze-on type derailleurs. The hanger likely will not allow the derailleur to be lowered enough. And replacing the braze-on with a clamp-on is not a good idea on a carbon fiber frame.
    Otherwise I like the idea.

    Al

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