# 105 cassette 10spd/11-25 to DA 7900 10spd/11-28



## trekbiking (May 18, 2009)

Hello. I just bought a Trek 2.3 with 105 compact group with ultegra short cage Read Der. I tested it up and down the hill but i felt like i needed more gear for uphill. So i'm thinking of replacing the 105 cassette 11-25 to 11-27/28, unfortunately 105/Ultegra doesn't make such cassette so i'm stuck with DA 7900. I just need more info before i buy it. Here are my concerns:

1. Does the DA 7900 cassette compatible with the hub and the ultegra short cag?.
2. Do i need to replace the stock chain which is pretty much new? If i do does it have to be a DA also?
3. Is there any other parts i need to buy to replace the cassette?
4. Any special steps i need to be concern about when replacing. (i'm a newbie rider and know little about new bikes but determine to learn bike maintenance so i can do my own

Thanks.


----------



## ukbloke (Sep 1, 2007)

trekbiking said:


> So i'm thinking of replacing the 105 cassette 11-25 to 11-27/28, unfortunately 105/Ultegra doesn't make such cassette so i'm stuck with DA 7900.


I'm curious about this too. Note that there is, or soon will be, an Ultegra CS-6700 11-28 cassette which would be a much cheaper and probably more durable option than DA. 

I am currently using 12-27 with a compact 50/34, and see some advantages for 11-28. The 11 cog is nice with a compact for hill descents, while the 28 gives slightly lower gearing for the really steep hills. Of course you pay for this with increased gaps between the cogs, and this could be pretty annoying for some ratios.

> Does the DA 7900 cassette compatible with the hub and the ultegra short cag?.

You are definitely beyond the capacity of the short cage derailleur. The compact 50/34 gives 16, and the rear 11-28 gives 17 for a total of 33. The official spec is 29. I have heard of people using the SRAM 11-28 cassettes with some success. I think this is pushing the limit and you will have to try it to see how well it works on your bike.

Because of this, I decided to stick with the 12-27 cassette and not attempt this upgrade. Officially 12-27 is beyond the capacity limits too, but it is "well known" that it works.

> 2. Do i need to replace the stock chain which is pretty much new? If i do does it have to be a DA also?

I think you can stick with the existing 10 speed chain (though it will need to be longer!), and that there is (sufficient) compatibility between the 7900/6700 cassettes and current Shimano 10 speed chains. This may not be as preferable as a complete 7900/6700 transmission, but I don't think you want to upgrade to the new chain either since you don't have the 7900/6700 chain rings. You might want to do some more research on this. Perhaps you should have asked this question in the "components and wrenching" forum.

> 3. Is there any other parts i need to buy to replace the cassette?

Tools to remove the old cassette and install the new cassette. This is a chain-whip, the cassette removal tool, and a big wrench. Also you will need extra links in the chain to increase from the 25 cog to the 28 cog, so you will likely need a new chain after all. And then you will need a chain tool.

> 4. Any special steps i need to be concern about when replacing. (i'm a newbie rider and know little about new bikes but determine to learn bike maintenance so i can do my own

Read the instruction at the Park Tool web-site. The order and orientation of the cogs and spacers is important, so pay close attention to this as you remove the old cassette. You will probably need to adjust the rear derailleur, particularly the B-screw to adjust for the increased side of the largest cog. Also pay close attention to chain sizing and make sure that the big/big combination will work without stressing anything. The Shimano instruction manuals are very good too.


----------



## bec143 (Mar 26, 2008)

I have A Roubaix Comp that came stock with an Ultegra short cage rear and a SRAM 11-28 cassette. It was a little rough at first, but a lbs took out a chain link and moved the habger a bit and it has been flawless for a year.


----------

