Does anybody have a real world experience with the 28 and Di2. The 7900 is compatible with the 28, but the Shimano rep says its a no go. So before I drop some money for a new cassette does anyone know if this combo works. Thanks

Here's the manual
Official spec is 11-27 max rear with 32 tooth capacity.

11-28 is 17 of the 32 teeth, leaving 15 in front. So even if you make the leap to 28, with 34-50 in front, you'd also be one over capacity.

Dura-Ace has traditionally be able to deal with over-capacity, but I'll leave Di2 to others to comment on.

Madcow did it. Check with him for results.
You could also try a 10 tooth upper pulley to give you that little extra spacing.

I did a local (pretty steep) hill climb with Di2 on my Cervelo - Compact (50/34) up front and an 11x28 7900 Cassette. Was *definitely* in the 28 a bunch of the time !
No issues whatsoever. Multiple people in the race had mis-shifts - so it was a treat to have Di2 on such a steep beast - Bohlman-On Orbit-Bohlman.

Mine works just fine in the 28/11 range(Giant 2010 Advanced SL Limited Edition). I don't use it much but it works and no problem with the Di2. Di2 is the sh!t. I wish the new Parlee Z3 I just built up had internal wiring but the Campy Record Red 10 will have to do.

Thanks for all the help. I am going to order a 11x28 and give it a try. I am running a 39x53 up front and have been running the 12x27 without issues. Thanks again

Sorry for the hijack, but timsterc, I am interested in how you got your FD to work with the compact crank. On my R3, I had to do a slight bit of "dremel'ing" on the front derailleur mount to put the Di2 on with regular 7900 cranks. There has been some discussion on the Cervelo forums on this. Did you have to remove any material from you FD mount on the R3SL to get this to work?

http://forums.cervelo.com/forums/t/5190.aspx?PageIndex=1

Yes - had to remove a good little bit to get it low enough for the Compact - so that the Di2 'connector receptacle' could clear the FD mount.

This is great info. Thanks! Is there any way you can provide a picture of what you've done so I can replicate on my bike. If you've taken a look at the link I've provided, There's a picture of what I did. It would be great to compare and see how much more I need to grind.

I've managed to successfully use Di2 on my mtb granted it's only a 29/42 in the front, it is running on an 11-32 cassette in the rear without any problems.

Not the best image - but you can see where I removed material. Since swapping back to mechanical DA - I painted that area black, so it's harder to tell.

Perfect! Thanks for confirming that this is possible, and that the integrity of the FD hanger is maintained. This has to be the case because you've gone back to mechanical on this bike and all is good.

Di2 with SRAM XX 11-34!!!

Better...11-36 cassete

UPSIDE,
Did it work out for you?