# Can I run a 12-28 Cassette on my Dura Ace 7800?



## Taskmaxter

I like the idea of going from my 12-27 to the 11-28 on the rear with my Dura Ace 7800, but I prefer to keep the 12 ring. Is there any way to go to a 12-28? I know Shimano doesn't make this, but am curious if any others have tried to do something similar on their Dura Ace.


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## shaochieh

Sure, I am running 11-28 on my Ultegra SL.


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## Taskmaxter

My guess is I can't mix the rings from my 12-27 with the 11-28, right? If my assumption is right I would have to go with a different cassette company to get a 12-28 (not sure who even makes one).


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## ukbloke

So you are thinking of buying an Ultegra 6700 11-28 and mixing and matching cogs with a DA 7800 12-27? I see no reason why this wouldn't work, possibly with slightly sub-optimal shifting at the transition point. You can find various charts on the Shimano web-site to figure out where to transition - I think both have the biggest 3 cogs on a carrier. If it doesn't work out you can always run the new 11-28 as is. You might need to lengthen your chain depending on whether there is any slack left over for the extra tooth.

If your only motivation is to get the lower gear, a 28 is only very slightly lower than a 27 and I'm not convinced that it will make a meaningful difference.


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## wrshultz

*Making a 12-28 10-spd cassette*

I'm pretty sure you can mix the SRAM PG-1070 cassettes to make a 12-28 10-speed.

The top three cogs are on a carrier on both the 11-28 (22-25-28) and 12-25 (21-23-25).

You use the 12,13,14,15,16,17,19 from the 12-25 with the 22-25-28 from the 11-28.

From what I've heard (no pun intended) the PG series is quieter than the OG.

You might be able to do this by mixing the newer 6700 or 7900 Shimano cassettes, but don't know anybody that's tried it yet.

Hope this helps.

Bill


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## Taskmaxter

ukbloke said:


> If your only motivation is to get the lower gear, a 28 is only very slightly lower than a 27 and I'm not convinced that it will make a meaningful difference.


Yes, this pretty much sums it up. I'm not sure if it would be meaningful as well, but was just contemplating it. I do a lot of steep climbing around where I live and was trying to give my knees a tiny bit more of a break, but an extra tooth might not do much.


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## Spin42

My understanding is you can make a 33 tooth chain ring work with a compact crank, might be worth a try. Much cheaper, should offer more relief then a 28 tooth on the back with a standard 34 tooth sprocket up front. You can get the chain ring here http://www.peterwhitecycles.com/chainrings.asp

If you have problems dropping your chain you can try a chain watcher or chain catcher, not sure exactly what it's called.


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## sometimerider

Spin42 said:


> My understanding is you can make a 33 tooth chain ring work with a compact crank, might be worth a try. Much cheaper, should offer more relief then a 28 tooth on the back with a standard 34 tooth sprocket up front.


I don't see how going from a 34 to a 33 ring is better than going from a 27 to 28 cog. In fact, it's less of a gearing reduction. The former is a 2.9% reduction; the latter is 3.7%.


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## Spin42

According to the gear calculator on Sheldon Brown's site we're both wrong. They're the same, 2.4%.


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## RHankey

At those tooth sizes, a one tooth difference on the front or rear is not going to make much difference.
34Tx27T=34in
34Tx28T=32.79in
33Tx27T=33in
33Tx28T=31.82in


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## sometimerider

Spin42 said:


> According to the gear calculator on Sheldon Brown's site we're both wrong. They're the same, 2.4%.


I don't know what you were looking at on Sheldon's site, but they're not the same. RHankey has the right numbers.

Clearly a change between 27 and 28 is more significant than a change between 34 and 33 (but the differences are indeed quite small).


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## MarvinK

You could do a 12-28 IRD cassette... those are available.


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## framesti

Do you have to change chain length/ rear shifting using both 27T and 28T cassettes?


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## ukbloke

framesti said:


> Do you have to change chain length/ rear shifting using both 27T and 28T cassettes?


No, after you size the chain for the 28T (e.g. by following manufacturer's instructions), then any cassette with a smaller biggest sprocket will work without any change. RD limits and tension do not need to change either.


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## Ryder321

Taskmaxter said:


> I like the idea of going from my 12-27 to the 11-28 on the rear with my Dura Ace 7800, but I prefer to keep the 12 ring. Is there any way to go to a 12-28? I know Shimano doesn't make this, but am curious if any others have tried to do something similar on their Dura Ace.


From the Shimano website:


*NOTE: CS-7900 11-27 and 11-28 require the use of RD-7900 or RD-6700

NOTE: CS-6700 11-28T requires the use of RD-6700 or RD-7900.* 

I vaguely recall reading that others have successfully used a 28T cassette cog with older model Shimano derailleurs, but I could be mistaken. Absent full return privileges, I'd heed Shimano's warning.


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## thechriswebb

Those measurements give a little bit of margin for error. Of course, I'm on 6600, but I bought a SRAM 11-28 and it works fine with absolutely no problems whatsoever. I bet a 30T cog would work just fine....

Once you start getting into those bigger cogs though, you need to be more conscious of your shifting and aware of crosschaining.


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## vladvm

yes. i have sram 12-28 cassette and DA-7800 drivetrain no problem.


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