Originally Posted by
Eulers
*Will a 140mm hub and 40-spokes (20/20) properly support use of 11-speed with a 295# husband/wife team?
*If I go with Da Vinci cranks, then what do I need to measure on my existing frame so as to spec the front and rear Da Vinci cranksets and bottom bracket?[*]
*Will the new Ultegra R8000 mechanical group still shift well when used with the extra long derailleur cable needed for a tandem frame?
*What concerns are there for chainline dimensions during this build?[*]
*From a standpoint of future-proofing one's investment - What is the potential for the manufacturers to release a roadie 12-speed, for double chainrings, in the next 6-months?
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Your 11sp upgrade is feasible, but is it worthwhile to spend around $1,400 to get a modest improvement in shifting on a 20 year-old frame?
The DaVinci cranks use square taper BB to fit 68mm shells, and the arms come in a wide range of lengths. Retail is around $600.
The Ultegra R8000 11sp mechanical will be fine with the long cable run. The front shifting will be better than a triple, esp if you use high quality rings with ramps and pins. However, Di2 or eTap will be substantially better than any mechanical drivetrain. Chainline should not be an issue. The cost for R8000 shifters, derailleurs chain, and 11sp cassette is around $500.
Shimano is much more likely to introduce a 12sp group for mtn bikes rather than for road bikes. This would be to match the SRAM Eagle 1x12 drivetrain. Some gravel bikes use 1x12 but it's a niche market. Regardless, 11 and 10sp road groups will be around for a long time.
It will be hard to find a 11sp rear hub with the old 140mm spacing. Even if you find one, the rear hub (without rim or spokes) will probably cost $300+.