11s Ultegra Di2 vs 12s 105 Di2
 

I'm looking to buy/build a bike in the coming year, likely sometime this fall, and have been thinking about groupset choice. I'm primarily a racer so my decision would mostly be performance-oriented, but I'm not closed off to other suggestions.

My budget is rather tight (around $2500) so I may, in actuality, be restricted to 11s only. That being said, I'm curious to hear people's thoughts. My personal considerations are:

Ultegra 11s Di2
- lighter by about 328g/0.72lbs
- probably less expensive
- Nicer materials
- I've heard shifting quality may not be on par with 12s 105 Di2
- Do I really need the extra gear?

105 12s Di2
- extra gearing
- supposedly better shifting performance

At the moment I am leaning towards Ultegra but am slightly worried about the ease of finding parts in the coming years, though I really hope that won't be an issue.

I'd recommend looking beyond the weight and going with the 12spd 105 kit if you're starting from scratch with DI2.

I'd say the shifting performance over the two (11spd and 12spd) is very close, but the ergonomics on the 12spd is far superior IMO. And your comment on long-term parts availability is totally valid.

I've got 12spd DI2 kits on various bikes, DA, Ultegra, and 105. The shifting performance in imperceptible. The "feel" at the lever is slightly different, as is material feel. On-road performance is what really matters though, and 105 has it for a fraction of the cost.

consider reliability.

i've got a couple of bikes with Ultegra 11s DI2, which have been trouble-free.

but i do have friends on 12s 105 DI2 who have had the FD replaced in the first year of use. Has anyone else heard of this?

I'd look at the cassettes and see where that extra gear is. E.g. Campy 12-speed offers the extra gear on the high end of the cassette, which served no use for me instead of putting it in the middle to minimize jumps, or at the low end for climbing.

My two main bikes are these groupsets. Road bike with 11s Ultegra, gravel bike 12s 105.

Performance is very similar between the two. I'd give the slight edge to the Ultegra setup, but I can't say that isn't due to the slightly different cassette ranges (11-30 vs. 11-34) or hanger alignment or something. Both work very well in any case and I would not decide on that.

Ergonomics are fine on both, IMO. Ultegra has the hood buttons if that matters. 105 is wireless levers which makes for easier installation, but a bunch more batteries to deal with. Ultegra levers have servo wave for better modulation.