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Old 06-18-12, 01:45 PM   #1
delcrossv 
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Which is the rear derailleur with the largest chainwrap (capacity)

I'd like to run a 53-42-24 front and an 11-34 rear on a touring bike I'm putting together. I think that adds to 51 teeth by the usual formula. Will a shimano SGS work or is there another 9 speed with more takeup capacity?
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Old 06-18-12, 01:48 PM   #2
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I'm running 22/32/48 with 11-36 cassettes on two bikes.
That is also 51 teeth.
I use the 9s "Shadow" RD's.
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Old 06-18-12, 01:49 PM   #3
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The custom one Chuck Harris [of mirror making fame] made for his unique bike.
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Old 06-18-12, 02:16 PM   #4
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With a triple crank, you can exceed the wrap capacity to some extent.

I would suggest having a long enough chain to shift into big/big (use the big/big + 1" method). Even though you shouldn't use this combo, it should shift there just in case.

If this causes the RD to fold up and the chain goes slack in small/small that's okay since there's no reason to ever use this combo either and you'll be able to get out of that combo when the mistake is realized.

That all said, Shimano's SGS (long cage) mountain RDs have all the same wrap capacities, so any will work (with the usual warnings about 10-speed Dina-Sys cable pull ratio incompatibility and Rapid Rise low-normal backward-ness).
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Old 06-18-12, 05:43 PM   #5
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I run a 20 43 on the front and a 12 39 on the rear a standard shimano megarange works fine on this setup. http://www.flickr.com/photos/6337399...in/photostream
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Old 06-18-12, 06:19 PM   #6
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A deore or any mountain bike rear works fine. I don't like the latest and greatest because they don't an adjustment screw on the Der..
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Old 06-19-12, 05:32 AM   #7
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Quote:
Originally Posted by JiveTurkey View Post
With a triple crank, you can exceed the wrap capacity to some extent.

I would suggest having a long enough chain to shift into big/big (use the big/big + 1" method). Even though you shouldn't use this combo, it should shift there just in case.

If this causes the RD to fold up and the chain goes slack in small/small that's okay since there's no reason to ever use this combo either and you'll be able to get out of that combo when the mistake is realized.

That all said, Shimano's SGS (long cage) mountain RDs have all the same wrap capacities, so any will work (with the usual warnings about 10-speed Dina-Sys cable pull ratio incompatibility and Rapid Rise low-normal backward-ness).
That’s exactly how I did it. I also had to make the chain longer by one link to make the big / big combo. I have 52,42,24 front and 12-36 rear. Just make sure you can shift into the two big ones and don’t worry about the slack on the small / small as you will never get over there. It is easy to forget you are on the big ring though and shift to far in the back.


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Old 06-19-12, 05:39 AM   #8
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Quote:
Originally Posted by JiveTurkey View Post
With a triple crank, you can exceed the wrap capacity to some extent.

I would suggest having a long enough chain to shift into big/big (use the big/big + 1" method). Even though you shouldn't use this combo, it should shift there just in case.

If this causes the RD to fold up and the chain goes slack in small/small that's okay since there's no reason to ever use this combo either and you'll be able to get out of that combo when the mistake is realized.
That's what I think too. I can easily imagine a situation in which I might accidentally shift into the big/big but I've never ever used my granny gear with any but the biggest two or three rear cogs.
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Old 06-19-12, 07:01 AM   #9
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I'm going to play curmudgeon and not speak to your original question. I'll leave alone for the moment how much you will use any of the higher gears, although your choice of a 53 large does come into play. Because you went that large you are somewhat forced to go larger on the middle ring. Because you also chose an extremely low range for the granny you then have a huge jump between that and the middle. The effects are this:

You have a 75% jump in gear ratio between the granny and the middle gear. Perhaps that is acceptable to you because you anticipate a lot of steep/difficult climbing, and the granny is typically not used as much.

HOWEVER, because the middle ring is relatively large, the lowest gear combo on it would yield about 9 miles per hour at 90 rpm (8 mph @ 80rpm). If you go any slower than that you will be forced onto the granny. If you are doing fully loaded touring, which I would expect when you are going for such a low granny range, those speeds could be quite common, resulting in too frequent shifting and a lot less enjoyment.

If you are planning a 10 speed cassette it's not nearly as ideal as a 9 speed, but the common 48/38 combo came about for a reason, and I question if the "benefit" of pedaling downhill at 40+ mph rather than tucking down and coasting is worth the cost of messing up the useability of the middle ring.

p.s. On the topic of too frequent shifting, I found out the hard way that there is one decided downside to brifters for touring that I had not anticipated. When I was on a tour in Italy I had a much longer and much hillier day than anticipated (long story). As a result I was using my left brifter very frequently. As the stroke required for a chainwheel shift is fairly long and requires more force than a rear cog I ended up with a sore hand.

Last edited by cny-bikeman; 06-19-12 at 07:35 AM.
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Old 06-19-12, 07:24 AM   #10
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If you are planning a 10 speed cassette it's not nearly as ideal as a 9 speed, but the common 48/38 combo came about for a reason, and I question if the "benefit" of pedaling downhill at 40+ mph rather than tucking down and coasting is worth the cost of messing up the useability of the middle ring.
My view as well. I would sacrifice the 53/11 combo that will see very little use, and reduce the size of the middle and outer chainrings slightly. 48/11 still gives you 113 gear inches with a 26" wheel.
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Old 06-19-12, 07:29 AM   #11
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I have a top gear of 48/11 on my climbing road bike and my touring bike, and a top gear 53/11 on another road bike. The 53/11 is rarely used, generally only on descents of -9% or more when I feel the need to break 45mph.
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