So I decided to change my crankset on my commuting/grocery getting/everything else bike from a more touring/mtb oriented 24-36-[46 or 48 - I counted twice and got 47 both times] Biopace crankset to a more road oriented triple. I got a good deal on a late 90's RSX 30-42-52 crankset that should be able to use my current BB (JIS square taper - I wanted a triple because I like triples and also a triple would mean not having to replace my bb as opposed to a compact double which would require a different spindle length). So far so good, right?
Because I'm getting a larger big chainring I also decided I should get a new front derailleur (heck, the oval of the biopace was probably pushing the tourney FD I had on there). I found a new in box 105 5603 FD on ebay for ~$15 shipped, so I figured I was good to go (NIB was important because that meant it came with the 28.6 to 31.8 mm shims that most people try selling separately on the bay for another $10 - or they've just tossed if it's used).
After I won it last night, I was looking more closely though and realized that I'd looked at the spec sheet for an older 105 FD (maybe 5503?) that could handle a 52T big ring and a 22T difference. Apparently, the 5603 version is optimized for 50T and a 20T difference.
Is this like rear derailleurs where the makers are overly cautious about the capacity and it can actually handle a few more teeth without a problem, or will this be an issue?
I friction shift if that matters at all.
Also, I read that Sheldon wrote that even though this is a 10 speed FD made to work with 10 speed chains, it should work just fine with the wider 8 speed chain. Is that still true? I'm going to be using a 7 speed freewheel on the back.