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Dura Ace 7900 crank/cassette limits

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Dura Ace 7900 crank/cassette limits

Old 05-29-10, 01:52 PM
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Dura Ace 7900 crank/cassette limits

My new bike has a DA 7900 11-23 cassette, derailleur, and compact crank and chain. I was thinking I needed a little more help with the hills so I got a Ultegra 11-28 cassette. The new 7900 DA is suppose to handle the 50-34 compact with a 11-28 no problem. Unfortunately it does not. If I cross chain from the 50 to the 28 the chain is stretched too tight and rubs a pin between the two idle wheels in the derailleur. I then noticed a note in the derailleur instructions that states, "add two links to the chain for an 11-28." Humph. I guess I'm going to take back the Ultegra 11-28. I don't want to buy a $70 chain just to add 2 links. Also the bike techs say the chain is finicky and I should not monkey with breaking it if possible.

I know I shouldn't cross chain but setting the front derailleur cable tension requires you do it (at least on the stand) and listen for chain rub. Also I just don't want to end up in the 50-28 com bo on a ride and screw things up. So my question:

Since the note about 2 extra links in the instructions seems to only apply to the 11-28, can I assume an 11-27 should JUST fit? I know I'd like the climbing gear while I work off these extra 20 pounds. Also, is the geometry of the Ultegra and the DA cassettes IDENTICAL? Should I expect great shifting albeit with a few more grams with the Ultegra? I'd rather not spend $100 more for a faster wearing cassette just to save 1.5 oz!
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Old 05-29-10, 05:25 PM
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I would go with a 12-25 and keep the chain. If you work those hills after a while you will probably be fine with the compact. I did the opposite I had a 12-25 compact and went to an 11-23 but I live in the flats and the old marathoner has wind. 12-25 will allow you to use all ten gears in either ring, and you can cross chain for short periods. I ride in the 50-21,19 all the time it works and for a small time go to the 12-23 rather than make the front shift. 34-25 is a good gear.
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Old 05-29-10, 05:35 PM
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You don't have to cross chain to set up the front derailleur. You should get a new chain so it's the correct length, or don't cross chain.
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Old 05-29-10, 06:14 PM
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You have two options:

1. Use a cassette with a smaller big cog so that your chain is no longer too short
2. Buy a new chain and set it to the correct length to handle the 28T large cog.

FYI, you don't need to use the Dura Ace chain. Any 10 speed chain will work and the Ultegra 6700 chain will likely work just as well as the Dura Ace chain (just like the cassette). Ultegra 6700 chains can be had for ~$45.

You do NOT want to ride a bike with a chain too short to handle the big/big combo regardless of how conscious you are about cross-chaining. It's a disaster waiting to happen.
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Old 05-31-10, 06:20 AM
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As well as changing the chain length when changing the cassette to something with a larger cog, you may also have to adjust the B-screw on the rear derailleur (Park Tools or Sheldon Brown should be able to tell you how to do that).

BTW, the 12-28 10-speed cassette sold by BBB or IRD is way better than the 11-28 sold by Shimano and SRAM because the former has fewer large jumps between cog sizes (and a 50-12 is a big enough gear if you learn how to spin the pedals at a high cadence when necessary).
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Old 05-31-10, 01:56 PM
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I'm now looking in to a sram 11-26 or possibly a DA 11-27 on ebay if I can get it for around $100. As for 50-12 being big enough, you're probaby right. I rarely go to the 50-11 now except for fast downhill. As for the B nut, it is easy to adjust but I have never found it necessary. The idle wheel is not close to the cobs. In fact, I'd like it to be closer but no adjusting of the b nut will get it closer.
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Old 05-31-10, 04:38 PM
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Originally Posted by I_bRAD
You don't have to cross chain to set up the front derailleur. You should get a new chain so it's the correct length, or don't cross chain.
^^ Did you miss this?.. You need to put it on small/big and big/small on front/rear respectively..those are the ones you should be worrying about chain rub on.

Did you get the 11-23 DA cassette all greasy or do you want to keep it? The bike shop should exchange it for an 11-25 DA no problem..
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Old 06-07-10, 11:54 PM
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Originally Posted by tonski
^^ Did you miss this?.. You need to put it on small/big and big/small on front/rear respectively..those are the ones you should be worrying about chain rub on.

Did you get the 11-23 DA cassette all greasy or do you want to keep it? The bike shop should exchange it for an 11-25 DA no problem..
The chain doesn't rub the Ft. derailleur at all. It does rub the pin that is between the two idle wheels on the rear because the chain is too short. Also, I have put 700 miles on the 11-23 so it is probably too late to swap. I'm probably just going to put on a 6700 11-27.
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Old 06-08-10, 09:14 AM
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If I lived in Seattle I'd probably want a 12-28 or 11-28. Buy a new D-A chain, the nickel plating is worth the extra money in a rainy environment. If the old chain is not stretched maybe your LBS will have a couple of extra links you could add. Always use the special pin at each joining point.

Last edited by Al1943; 06-08-10 at 09:22 AM.
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