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Dura Ace - 7900 casette on 7800 groupset


Tjokkits
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Hi guys I now need to replace my DA casette so I have the 7800 and those casettes were discontinued one now has to use the 7900, only thing they say 11-27 and 11-28 wont work on 7800, but i saw on some overseas forums some people did it and it worked. So before I fork out cash is there any hubbers who tried this, and what was the outcome?

 

Thanks

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The Shimano Dura Ace CS-7900 Cassette is compatible with the Dura Ace RD-7900 rear derailleur and the RD-7800 rear derailleur except for 11-27 and 11-28 . The RD-7800 rear derailleur does not have ample chain wrap capacity to handle the CS-7900 in 11-27 and 11-28. These cassettes must be used with the RD-7900. The CS-7900 is optimized for the Dura Ace CN-7900 chain, but it is compatible with the Dura Ace CN-7801 chain.

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The Shimano Dura Ace CS-7900 Cassette is compatible with the Dura Ace RD-7900 rear derailleur and the RD-7800 rear derailleur except for 11-27 and 11-28 . The RD-7800 rear derailleur does not have ample chain wrap capacity to handle the CS-7900 in 11-27 and 11-28. These cassettes must be used with the RD-7900. The CS-7900 is optimized for the Dura Ace CN-7900 chain, but it is compatible with the Dura Ace CN-7801 chain.

 

Sounds like a whole lot of marketing to get you to buy a new RD. Unless the 7900 is actually shorter than the 7800? Which I doubt

 

Some time ago I was told that I could not use a 9speed Dura Ace RD with a 10 speed grouppo ... after installing it I went back to show them it works perfectly. The speed of an RD is determined by the shifters, nothing else! The shift increments differ from 9 to 10 speed.

And the total width of the cassette between 9 & 10 or 11 speed cassettes has not changed.

 

That 9 speed RD of mine will be able to handle 11 speed cassette, no problem.

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