# What cassette can I run on my Dura-Ace 7800 rear derailleur?



## MAS-SD (Jun 14, 2008)

I have worn out my 11-23 Dura Ace 7800 cassette. I managed to get over 13,000 miles on it, but it's running on vapor right now.

I climb a lot on a majority of my rides and want a less aggressive cassette this time around. My front chain-rings are 53-39 on a compact crank. I want to go with an 11-28T, but the specs on the 7800 derailleur state that I can only go to a 27. 

Has anyone had success with an 11-28 on this rear derailleur or should I just go with the 27.

Thank you.


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## SilverStar (Jan 21, 2008)

While I haven't personally tried it, I've heard many tales right here on RBR and elsewhere that an 11-28 works fine with that derailleur. Word is that the Shimano specs are a touch on the conservative side -- but 28T is about the biggest I'd try if I were so inclined.


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## frdfandc (Nov 27, 2007)

You can pick any size up to a 28 tootj. Shimano does state their max size for your RD as a 27, but there is wiggle room with a b-screw adjustment.


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## MAS-SD (Jun 14, 2008)

Great. Thank you for the advice. 11-28 it is.


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## ukbloke (Sep 1, 2007)

You will be fine with the short-cage RD using the 11-28 in combination with the 53-39 chain rings. However, if you plan to change the front out to 50-34 (because you say you have a compact crank presumably meaning 110mm BCD), you will be well over the RD capacity and pushing the limit.

Also note that you are going to have a lot of missing sprockets and a lot of big jumps going from an 11-23 to an 11-28. You should look at a gear chart to see whether this is a good trade-off. I would look at how much you use the 16T and 18T today, whether you can tolerate the 4T jump from 24 to 28, and also ask yourself whether you really need that 11T.


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## frdfandc (Nov 27, 2007)

Double post


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## pmt (Aug 4, 2009)

11-28 and 50-34 work perfectly with a DA7800 rear. No trouble at all, if setup correctly.


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## durielk (Jan 8, 2011)

Ditch those 53/39, you can't spin that 53 anyway & get a 50/34 with 11/28. It will work with your short cage. As for the miracle "16", the 50x21 is within .5mph & the 34x14 is exactly the same gearing. Go with the 12/27 if you don't ride any long grinding hills @ over 14%. But if you do high speed training rides, you will want the 11 when your cruising at 28mph.


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## ukbloke (Sep 1, 2007)

durielk said:


> As for the miracle "16", the 50x21 is within .5mph & the 34x14 is exactly the same gearing.


It's not that 16T has miracle properties, it is that if you naturally end up around in the middle of the cassette around the 17T cog then your next up and down gears are 2T away, and those > 10% percentage changes can get pretty annoying (for some). I only pointed it out as the OP is coming from 11-23 which is getting toward a straight block other than the climbing gears.


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## ukbloke (Sep 1, 2007)

The other thing is that if the OP goes from 53/39 x 11-23 to 50/34 x 11-28 for the same terrain that he/she's been riding for 13,000 miles, that sounds like a total capitulation to the hill to me. Sure climbing will be a lot easier, but chances are you'll be going slower too, unless you compensate massively with cadence and/or self-restraint with all those easy gears.


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## durielk (Jan 8, 2011)

Ditch those 53/39, you can't spin that 53 anyway & get a 50/34 with 11/28. It will work with your short cage. As for the miracle "16", the 50x21 is within .5mph & the 34x14 is exactly the same gearing. Go with the 12/27 if you don't ride any long grinding hills @ over 14%. But if you do high speed training rides, you will want the 11 when your cruising at 28mph.


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## durielk (Jan 8, 2011)

If your worried about over 1T separation... switch to the small chain ring.. bingo you can have your 1T separation. Personally I only worry about the 1T separation over 20mph. With the setup I stated, after you spin out the 34, you hit the 50 with the 15 and it is all the way 1T to as fast as you can pedal.

If your going to get away from the straight block, you have to start separating the gears somewhere, otherwise just stay with the 11-23 and SUFFER!


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