Need a 12-27T (max allowed on a DA Di2 RD) cassette for very ossasional use (Rides with 25-33% climbs).

Don't think I can stretch to a 7900 before I'll need it in 3 weeks time, so my options are an Ultegra 6600, or 105 5700. It seems Ultegra 6700's are 25T or 28T only, I cannot find a 12-27 anywhere.

So 6600 are older design, (different tooth profiles, jumpier shifiting under load?) but the 5700 will be heavier, so not sure which to pick.

Or will a 12-28T actually run on a DA Di2 RD?

Any advice welcome.

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Di2x2

Not sure if it would make much, if any difference - but what about PG1070?

I ran with 6700 RD FWIW, but not sure how it would be much of a problem for Di2?

I'd suggest a Recon cassette. They're very well priced, extremely light (120g for 11-27, lighter than 163g for Dura Ace 11-23!) and ideal if you're only using it occasionally. You can either get Al or Ti, Al being less durable but lighter and cheaper. Some people haven't had great luck with shifting but I run the Campag 10 speed one and it shifts like an absolute dream - never had any problems with it.

They come in 11-27T flavour so as long as you're not desperate for the 12T last sprocket then I'd say it's ideal.

By the way I don't think Shimano makes an Ultegra 10 speed 12-27? they only made one for 9 speed? They do make 11-28 though so I wonder if that will work with Di2...

Edit: After a bit of research it seems that indeed the largest sprocket you can use with di2 is 27T.

How about a Dura-Ace 7800? They're available in 12-27 on eBay.

Why not go for a 5700 cassette? They're only some 20 grams heavier than the 6700 cassettes, but work as well. Needless to say, they're cheap too.

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Flickr
2012 Cannondale CAAD10

First off, various sources report success with at least 28 tooth cassettes on a 7970 RD given proper B screw adjustment. If I was climbing those grades, I would want at least a 28.

http://velonews.competitor.com/2011/12/bikes-and-tech/ask-nick/ask-nick-shimanos-di2-gearing-compatibility-water-bottle-code-ti-seatpost_199011

I have no experience with 5700 cassettes, but I do with 6600 SRAM PG1070. The 6600 cassette shifts very smoothly and silently. However, I relegate these to my back up wheels in favor of the PG1070. Why? Although the PG1070 are noisier and slightly clunkier, they shift flawlessly under load whereas the 6600 will snap and ping in protest. I know the proper technique is to ease up during the shift but during a race, especially cyclocross that does not happen. I think riding style and preference would make the decision on the cassette. If you need to shift down to your biggest cassette sprocket while climbing a 25% slope, the PG1070 will shift smoother.

I think your derailleur should handle 28T just fine. I read an article on velonews where nick legan confirmed larger cassettes up 30t have worked properly on di2 cassettes. Madcow also modified di2 to work on a mountain bike, so I bet he would have a better idea as to what the REAL max cog size is. I say try it and see if it works. It certainly won't rip off your rear dérailleur.

I know its alot of money but I have a kcnc ti 12-27 and works flawlessly with Di2. It was Madcow advice to use this cassette.

105 12-27T cassettes must be available, I stock them. Miche do a cheap 12-27 cassette for shimano fitment which is fine ofor occasional use. Shifting is O.K with them as well. You may need to install a seconf 1mm spacer though depending on the hub as on one the cassette styarted to rattle after a few rides.

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www.thecycleclinic.co.uk

Yes, I am using DA Di2 RD and DA 11 / 28 cassette on my bike, they work fine.

Ok, great to know a 28t fits ok, thanks.

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Di2x2

25 to 33 % climbs, where does one encounter those ?

I was wondering that myself. I suspect there's some confusion between degrees and % grade.

I thought he meant that 25-33% as part of the distance ridden, consisted of climbs. Anyway, max tooth has just as much to do with the RD hanger on the frame, as the RD itself. What cassette/RD combo works on one frame, might not work on another.

The RD hanger alignment standard is not a precise science, with lots of small variations. If you're on the edge of what might work, those variations can very well be big enough to matter.

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Roadbike
Kinesis RaceLight T2

Mountainbike
Van Nicholas Zion Ti

Hanger shape is critical. For instance, a few specialized derailleur hangers come in standard, and long (for 28t or more).