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Old 06-13-06, 08:37 AM   #1
rick.seattle
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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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Old 06-13-06, 08:48 AM   #2
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105 Long cage or short?
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Old 06-13-06, 08:59 AM   #3
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Ah, good question. I'm not sure and the bike is at home.
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Old 06-13-06, 09:30 AM   #4
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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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Old 06-13-06, 10:20 AM   #5
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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.

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Old 06-13-06, 10:59 AM   #6
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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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Old 06-13-06, 11:15 AM   #7
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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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Old 06-13-06, 11:43 AM   #8
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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.

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Old 06-13-06, 01:12 PM   #9
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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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Old 06-13-06, 01:59 PM   #10
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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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Old 06-13-06, 02:03 PM   #11
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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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Old 06-13-06, 02:24 PM   #12
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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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Old 06-13-06, 02:55 PM   #13
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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.
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Old 06-13-06, 03:35 PM   #14
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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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Old 06-13-06, 03:49 PM   #15
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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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Old 06-13-06, 04:12 PM   #16
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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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Old 06-14-06, 10:43 AM   #17
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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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