Originally Posted by
rms13
It's all debatable really. The main reason I say Sora to Tiagra is because Tiagra and up all have the new brifter hood shape, new crank style and new style front derailleur. New Sora will have those features. Tourney to Claris is another jump because of the thumb buttons (Tourney still has thumb buttons, right?)
Just messing with you. It's as you say, there's two big jumps with the current lineup. 3500 to 4700 or 2400 to 3600 and Tourney to 2400. Sora 3600, from what I've seen will actually have the old style rear though. The lower number of gears gives each gear a longer amount of cable pull, so Shimano deemed the new pull ratio unnecessary even with under the tape cables and it probably lets them provide legacy support for the old pull ratio.
I tend to think "real" STIs are more important than hood shape, just my opinion, and the 4-arm crank overrated. The new cranks might be a stiffer if you're a crank bender, but they're also proprietary. Not just a proprietary BCD but the shape seems to be different for each tier so even if you mount rings they won't match up right.
I remember running the numbers once, FC-5750 is actually lighter than FC-5800 50/34. The Tiagra 4 arm cranks are heavier than the older Tiagra 5 arm cranks.
Tourney still has thumb buttons and still has bottom of the barrel (albeit functional) construction. Very plastic and lots of painted stamped steel, although Claris as a fair bit of it as well. Same RD found on Walmart bikes. Meant to be compatible with freewheels and so on.