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Old 06-16-09, 06:02 AM   #1
aharong
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Switching cassette: 12-26 to 11-34

I know that the issues of switching cogs and rings has been discussed ad nauseum, but I couldn't find an answer to my specific question in the archives.

My wife has a Trek 1000c which she likes. But she frequently tows 1-2 kids in a trailer and I think that she would benefit from a better selection of gears (specifically low end). I made some charts and did the math and decided that switching the cassette is more effetive than swapping out the entire crank and granny gear.

Her Sora rear derailluer maxes (according to Shimano specs) at 27T. So I intend to order a Deore M531 derailluer with the Deore HG50 11-34 cassette.

QUESTION: Can anyone tell me if her Sora STI brifters are compatible with the Deore derailluer?

This is similar to the road/mountain combo on my Cannondale T800 touring bike (105 STI & Deore XT), so I expect it to work. But I would love to benefit from someone elses specific knowledge.

Thanks.

Last edited by aharong; 06-16-09 at 06:47 AM.
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Old 06-16-09, 06:23 AM   #2
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I can't add an expert opinion, but the shifter depends on the spacing of the cassette to work, so as long as you keep the same number of cogs you should be OK. The big issue for such a large range (sounds like a Mega-Range cassette) is a RD with enough length to take up the slack you will have due to the big cog. I have used a number of these large rear cogs with a few different front shifters with no problems. You will probably need a longer chain as well.
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Old 06-16-09, 06:28 AM   #3
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if the shifter is 9sp, it will shift 9sp. if the shifter is 8sp, it will shift 8 or 7sp cassettes.
HG-50, if memory serves correct, is a 9sp cassette.

you will also need a new chain, probably at the full 114 link length if it's 50x34 and might be too short if it's 53x34
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Old 06-16-09, 07:20 AM   #4
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I have used a number of these large rear cogs with a few different front shifters with no problems. You will probably need a longer chain as well.
Cool.

Is there a way to know/guestimate the length of chain I'll need? Should I just add the difference in teeth to the length of the current chain (34T - 26T = 8 links longer than current)? Is the new MTB derailluer likely to require a couple more or fewer links?
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Old 06-16-09, 07:31 AM   #5
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Half of the 34/26 difference is probably closer (if you were usiung the same derailleur). But, since you aren't , you need to allow for the longer arm on the Deore. Just wait till you get it, then do the chain surgery.
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Old 06-16-09, 09:05 AM   #6
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Yes, the Deore derailer is compatiable with Sora shifters. You'll need a longer chain, since you're replacing the cassette, get a new chain.
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Old 06-16-09, 09:13 AM   #7
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Quote:
Originally Posted by aharong View Post
Cool.

Is there a way to know/guestimate the length of chain I'll need? Should I just add the difference in teeth to the length of the current chain (34T - 26T = 8 links longer than current)? Is the new MTB derailluer likely to require a couple more or fewer links?
Don't guesstimate.

Wrap your new chain around the biggest front chainring and biggest rear cog bypassing the rear derailleur entirely. Figure out where the shortest place you could join the chain. Add 1" of chain (2 links) to that. Believe it or not, the type of rear derailleur doesn't have to be figured into chain length calculations.
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Old 06-16-09, 10:28 AM   #8
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I ended up having to use all 114 links the sram 9sp chain comes with when using 50/34 and a 13-34 cassette on a CX bike.

the really cool part about using a deore long cage is that you don't really have to worry about having your chain too long.
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Old 06-16-09, 11:48 AM   #9
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Why would you want an 11t cog? Start with a 12 or bigger.
The cassette number of cogs needs to match the shifter.
Any Shimano mountain rear derailleur will work with the 34 cog.
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Old 06-16-09, 01:25 PM   #10
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Quote:
Originally Posted by AEO View Post
HG-50, if memory serves correct, is a 9sp cassette.
The HG50 designation is also used for 7 and 8 speed cassettes.

Quote:
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you will also need a new chain, probably at the full 114 link length if it's 50x34 and might be too short if it's 53x34
I put a 30/39/50 Tiagra triple and a 11-34 cassette on a Schwinn World Sport. I had 4 links out of 116 left over.
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Old 06-16-09, 01:43 PM   #11
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The HG50 designation is also used for 7 and 8 speed cassettes.



I put a 30/39/50 Tiagra triple and a 11-34 cassette on a Schwinn World Sport. I had 4 links out of 116 left over.
I have an 8 speed HG50, but it is from a 2k4 bike which explains it. Seems shimano moved to 9 speed on the more recent HG50's.
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Old 06-16-09, 04:21 PM   #12
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... if the shifter is 8sp, it will shift 8 or 7sp cassettes...
The spacing is just a little different, so be prepared if it isn't quite right. Most work, some don't.
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Old 06-26-09, 08:21 AM   #13
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Follow up: In the end I bought a Shimano 8-spd 11-32. I talked myself out of the 11-34 Megarange because in the 8-spd version there is a huge jump between the last 2 cogs, 26T to 34T. My wife tends to shift late, and it will be under load of pulling a kid trailer, so I thought the smaller step would be more important than the extra 2 teeth.

As somebody pointed out, 12T would have made more sense than 11T on the small cog, but the 8-spd does not come in that flavor.

I went with the low end Altus MTB derailluer to replace the Sora that came with the bike. I was looking for a transition, not an upgrade.

I had considered buying a cassette tool and even a repair stand, but in the end I chickened out and had the LBS do the work. The mechanic said he removed 2 links from the new chain (but he didn't mention length of new chain).

As you all predicted, the 8-spd MTB derailluer shifts perfectly with the Sora 8-spd brifters. I am thrilled with how it turned out. The wife has yet to ride it under load. But when she does I am sure to see some love.
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Old 06-26-09, 07:32 PM   #14
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Glad it worked out.
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