I have a 1983 Raleigh Super Course 12spd. I've put about 150 miles on it since I bought it and decided to check the chain stretch. It was between 1/16" and 1/8" 10 links out, which means the chain is stretched but the crank and cassette should be okay. So I go and order the SRAM pc-870 chain (3/32" x 1/2"), which is what Sheldon Brown recommends for bikes of this vintage.
I installed it, and didn't adjust the length at first, as the old chain was just as long as the new one. The chain skipped repeatedly under power on the two smallest cogs in the rear, the smaller of the two being MUCH worse than the larger.
Took two links out, same result.
two more links out, same result.
two more links out, way too tight.
put two back in, and just didn't use those gears for the ride.
I get home after a 45 mile ride and compare the old chain to the new; the new one seems to not fill the 'valleys' between the teeth quite as completely as the old chain does. I am left to believe that either the original chain was a 1/8" x 1/2", or the teeth are worn, but they certainly do not look 'ramped' by how it has been described to me and what I saw on Sheldon's site.
What do you guys think? If I do need a 1/8" x 1/2" chain, what might you recommend that is comparable to the SRAM pc-870? I will be doing collegiate races this spring, and the bike will usually see 100+ miles of hard riding a week.