Here are some more details on this increasingly interesting alternative to Alfine.
The trick with Ultegra Di2 is that it is 11-speed. This means an 11-speed hub (not compatible with 10-speed and smaller cassettes). Normally trikes use mountain bike hubs because the frames are designed for the 135mm dropout width. Unfortunately 11-speed isn’t really available yet in mountain bike groupsets and the new XTR Di2 groupset skips past 135mm to 142mm which probably won’t work on most trike frames. Besides, XTR Di2 is really really expensive and doesn’t seem to be available yet in the states. So that means putting a 130mm road hub on a frame designed for 135mm. I don’t think this is a big deal, I can use washers to fill the gap or (most likely) ignore it and let the frame flex inward 5mm to adjust. I won’t get whatever strength benefits 5 mm less dishing gets you (that’s apparently why the MTB hubs are wider) but I doubt it matters much on a road trike.
Other consequences of Ultegra Di2:
Everything is more costly with 11-speed of course. But it’s not too bad, especially if you use 105 instead of Ultegra where you can. Quite a bit cheaper than Alfine actually.
Requires a narrower chain which is more costly and apparently shorter life and more finicky. I gather the quick link is a one-time-use-only thing which is kind of weird. But not a showstopper (for me anyway). I’d happily replace the chain more often if it meant trouble-free shifting for the entire life of the chain.
Road derailleurs don’t have clutches like the new higher-end mtn derailleurs do. This theoretically would help with some chain management issues (maybe minimize skipping when going over bumps) but I’ve never had one with a clutch. So not really a feature I’d be losing relative to what I have now.
Not the best transition point between low and high range on Schlumpf compared with XTR or Alfine, but certainly workable. Just means I might be shifting the Schlumpf a little more often, and it requires the High Speed Drive instead of the Speed Drive to get a reasonable high end. But the range is quite good with almost no gear overlap.
You might have to give up a disc parking brake on the rear wheel. Disc brakes are still rare on upright road bikes and it doesn’t look like Shimano offers any 11-speed road hubs with disc brake capability. Most trike frames can accommodate a rear rim brake which would be my choice for a parking brake anyway, but some frames, like my Trice Q, don’t.
The least expensive component group for Di2 is Ultegra, but 11-speed hubs, cassettes, and chains go all the way down to the Shimano 105 group and should work fine with Ultegra Di2. The 105 hub and cassette each cost about $50 whereas the Ultegra versions cost about $100 and $70 respectively. A low-end 11-speed chain runs about $40 and the Ultegra Di2 derailleur runs about $230. Expensive compared to mid or low-range 9-speed components but not outrageous. And compared with Alfine-11 this setup is somewhere around $300 cheaper. Perhaps the best part is that degraded shifting will almost certainly be the result of some combination of worn cassette and chain, both easily and inexpensively replaced. In the case of Alfine you’re looking at repairing or replacing a $600 hub that is built into your wheel. Ultegra and Alfine Di2 can share all the same components except for the hubs, derailleur, cassette, and chain.
The obvious down side to Ultegra on a trike, and the reason I haven’t seriously considered it before, is that it doesn’t have enough range when coupled with a conventional front double or even triple crankset, and with a 20” drive wheel the range is shifted too low, compromising the high gears. Combined with a Schlumpf, however, both problems are solved with the added benefits of no front derailleur, no front shifter, and straighter/simpler chain line. Note that there are other IGH front cranks out there like the Truvative Hammerschmidt or possibly the Efneo, but none of them have anywhere near the 2.5:1 range of the Schlumpf High Speed Drive and they all require a shifter with mechanical cable. If content with the smaller 1.65:1 range of the Schumpf Speed Drive (I’m on the fence) and a mechanical cable (a showstopper for me), these other options are worth a look.
A factor that complicates my decision is that ultimately I’d prefer a mountain Di2 derailleur like the new XTR once it becomes more affordable (and truly available). The wider range lets me do most of my commuting without shifting the front at all and there might be some advantages to the clutch feature (not sure about that). But this setup would require the Speed Drive so upgrading from Ultegra with High Speed Drive to a mountain bike derailleur would also require switching to the Schlumpf Speed Drive, an incredibly expensive proposition. For this reason I’m considering the sub-optimal combination of Ultegra and Speed Drive.
Following are gearing charts for the widest range Ultegra cassette (11-32) paired with various choices of front crank. Schlumpf Speed Drive is nearly identical to Hammerschmidt and the front triple is very close to the Efneo.