Originally Posted by
dddd
I believe that matching-parts Alpha-3000 six-speed setup will work well with the substitution of any Shimano 9s chain.
The index shifter should be oiled internally and the cable housing loop should be clean modern housing with appropriate ferrules!
The cable indexing adjustment should be done first, followed by the low-limit screw, which should not intrude on the indexed low gear position!
Any 9s chain will work very well on a 6s Suntour freewheel, and the Shimano 9s chain has the narrowest pin width and widest sideplate reach of any 9s chain, which will really improve shifting performance, especially in terms of the service interval.
As for STI, I believe that any Sora shifters below the 9s 3500 vintage will discourage a rider from discovering the merits of a road bike's performance potential, due to not being able to safely shift to a higher gear from the drops. What total garbage (this rider's opinion).
I myself might add inexpensive Microshift 7s STI-style levers together with a Shimano or Microshift rear derailer, Sunrace 7s freewheel and narrower chain. The rest of the gruppo should be fine, and the brake pad posts can be cut down as needed.
Long-reach brakes may offer no improvement in terms of tire clearance unless some lengthening of the fork leg length exploits their added reach! I would not count on any newer caliper to improve tire clearance at all, though certain ones very well might (a little research is warranted imo).
The Nishiki is quite worthy of a modest upgrade budget imo, since your gas-pipe frame most likely has the best geometry for all around riding. Do make sure the headset turns most freely.
Have you ever ridden a bike with downtube shifters? I can assure you that shifting while in the drops is no big deal. It's loads easier than riding "no hands". In fact it's easy to shift with downtube shifters while in the drops, on the hoods, or on the flats, and many people find that's it's no problem to shift downtube shifters while standing and cranking/sprinting.
Why would you suggest using a narrow chain on freewheels and cranks with wide, uneven spacing between cogs? The narrower the chain, the worse the problem with wide spacing and narrow chain dropping or jamming between the cogs or chainrings. And the worse the problem caused by the uneven spacing between the high and low cogs on a Suntour spaced indexed freewheel will be.
There is nothing wrong with Ultegra 600, 105, RX100, and RSX 7 and 8 speed brifters that are in good condition. While older, they are made of better stuff than the plastic that Sora brifters are made of, and they are rebuildable, whereas Soras are not. 7 and 8 speed drivetrains have the same spacing as 6-speed systems and are more reliable, an less sensitive to adjustments than 9, 10, and 11 speed systems.
First generation dual pivot brakes (7 and 8 speed) are reliable, functional, accept wider wheels and tires than newer generations of dual pivot brakes, and are less expensive than the latest versions.