Hi I'm trying to decide I want to upgrade from the 7900 std group to Di2 etc what is the
Best choice for value and proformance. I'm oinly need the upgrade kit thanks

Value? Ultegra Di2 by a longshot. Performance? Don't look down and you can't tell the difference between the two. At least I can't, and I have plenty of miles on both. Cassette/chainring/chain choice has a far more dramatic impact on shift quality.

If you're just talking electric parts (shifters and derailleurs), weight gain is a little over 100g (104g on my scales, but the harnesses were not identical lengths so it could be slightly more).

Looks of DA Di2 are more sleek and refined. It also uses a wiring harness system that will likely be phased out by next fall, while the UDi2 harness has already been updated.

http://velonews.competitor.com/?p=187814

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Will the new DA Di2 will be compatible with UDi2? If we're sure it will be you could go with UDi2 but still have the option of upgrading individual parts in future.

I'm going through this at the moment. I would not even consider DADi2 if I could get some confirmation on satellite shifters being available for the UDi2 group. One difference worth considering. Everything else for me, bar aesthetics, points to Ultegra. I'm sure they must be doing the extra shifters for the new group, but no news so far I'm aware of.

Do the "Ui2" shifters have the dual sockets in them (one extra for the satellites) like the Di2 ones have?

If so, I guess they will come eventually, if not, how could the be supported?

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I disagree - the shift was noticeably slower on the U-Di2 bike I rode, and visually the rear mech is noticeably bigger (and therefore uglier) too.

Bang for buck is incomparable, but the details matter.

Are the shifters on U-Di2 smart? By that I mean, is there any electronics inside or is it like the dura-ace which just uses a simple contact closure for up or down?

I love the price of the U-Di2, but if I'm tied into the shifters as opposed to making my own (as other threads have shown) I'll be buying current design DA-Di2.

Scott

Agree with that. Front shifting especially. I can't imagine that someone who has ridden D/A Di2 doesn't notice the annoyingly slow front shifting of Ultegra Di2.

DA Di2 uses direct hard wiring for power and signals. Ultegra Di2 uses CamBUS comms protocol. This relies on a component I.D. signal, allowing the electronics "BUS" to correctly interpret and communicate with the component at the other end of the cable. Which is also why it allows for dummy-style connections where you can connect in any combination at the harness junction box and the system will still work as signal processing is by ID of component and not by specific connection points.

However, CamBUS will prevent you from so easily hacking the battery and extra buttons simply by just soldering extra connections. Since an ID is required for each component to communicate. It still can be done, but a much higher level of electronics comms knowhow is required. So, you're stuck with a standard setup unless you don't need those 'extras' at least for now. I believe we will see those auxiliary buttons and switches for Ultegra Di2 when DA eventually switches to the CamBUS protocal in about 2 years(when its up for revision). For now, probably not yet as I'm sure they don't wish to cannibalize their own products just yet.

Note, for current DA Di2, you can quite easily forgo the custom battery and charger by opting for a hacked battery pack using min-RC battery packs and chargers and saving a decent US$200/- or so in the process. Likewise, its possible to add additional shift buttons for under US$50 with some tinkering and soldering as demonstrated by some forum contributors here and over at Fairwheelbikes forums.

Some stuff to be aware of in the overall decision of things.

I noticed no such slow shifting, and in fact Shimano told me that in their testing they are virtually identical. Perhaps you were using UDi2 on sub-par chainrings? I've played with it on both Ultregra and DA cranksets. Shifting is a bit better on the latter.

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It was an Ultegra 6700 chainset.

on the other hand, i have heard the opposite, that ultegra di2 is slower and not so precise as DA di2, not saying that ultra di2 isn´t good. this was told to me by a shimano mechanic

I, too, have been told by

a) Shimano Multiservice guys
b) Shimano regional tech reps
c) Shimano higher ups

that front shifting on Ultegra Di2 is noticeably slower. As I recall, the tech rep said "We had to do something to differentiate it from D/A." I was told this after calling Shimano to try and figure out why I couldn't get Ultegra Di2 to shift as smoothly and quickly as D/A Di2.

From what I've seen of it ultegra di2 looks like they didn't bother with the finish machining of dura ace. The dura ace is chunky but the ultegra is agricultural. The only thing that I like about di2 is the front change everything else I prefer mechanical. If those reports are true of the slow shifting I'd choose mech da at the price point

Pretty good comparison on the front mech...

http://www.youtube.com/watch?v=mpGGrYs62CU

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