himespau 

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.

joejack951

What type of shifters will you be using? If friction shifters, expect to have to trim the front derailler frequently to avoid chain rub with the narrow cage 10 speed derailler. Perhaps you could switch to a 9 speed chain to make things a little better. If you have indexing shifters, you'll either need to live with the chain rub or buy a different front derailler.

As far as capacity of the derailler is concerned, you'll be fine with the 5603. I'm using one on my road bike with the same chainrings as you plan to run. Do note that the inner cage is optomized for an 11T difference between the outer and middle chainring. A 10T difference means you'll need to carefully set up the derailer so that it clears the middle ring when shifting to the outer ring but is not too high above the outer ring. It's possible with the 5603, not so with the 6603.

himespau 

hmm, maybe I should go for a 5503 (or even an 8 speed older one if I can find it) that's designed for the crankset I want to use. Feel stupid for looking at the wrong year's tech sheet. Didn't occur to me that they'd change the size of the rings between years, so I guess I didn't look closely enough.

joejack951

The 5503 will certainly be easier to setup and with a 9 speed chain will run flawlessly. If you want to keep using an 8 speed chain, this is your ticket: https://www.niagaracycle.com/product_...ucts_id=435717

Sorry for missing your comment on friction shifting in your first post. I need to "read" more and "scan" less sometimes.

motobecane69

more than likely it will work just fine, for the small amount you paid for it I would try it out first. My biggest concern is that you say you don't need a new bottom bracket. I'm not totally sure on this but I thought going from a double to a triple would necessitate a change in BB but don't hold me to it.

HillRider

No problem if it's on a friction shifting bike. I have a FD-5603 on my Surly Cross Check that has an 8-speed 105 triple crank (FC-1057) with 52/42/26 chainrings and an 8-speed SRAM chain. Shifting is by Shimano 8-speed downtube shifters on Kelly Take-Offs so the front is friction.

It works fine and requires a lot less trimming than I expected. I did have to mount it about 1 mm higher than ideal to get the inner cage plate to clear the 42T middle ring but shifting is good and clean even under load. You should be happy with the combination.

himespau 

Thanks for the input. Glad to hear that I should at least try my setup before buying something else. I've got the same Take-off/downtube shifter setup (I think you may have even been the one to recommend it to me), except I'm using 105 6 speed shifters as I currently have a 6 speed freewheel. The plan is to turn the little knob over to friction when I put the 7 speed freewheel on there because I'm pretty sure the one I'm planning on installing isn't indexable anyway (it claims to be shimano compatible, but I think that just describes the freewheel removal tool to use), and I don't really mind friction shifting.

I'm sure I'll have to make a few adjustments, but I doubt it'll be any worse than setting up my current tourney FD to deal with the oval shape of my biopace big chainring. Hopefully, it'll shift nicer too.

Sorry, I wasn't clearer. I have a triple currently and was trying to explain why I wanted to stay with a triple rather than go down to a compact double.

Yeah, I've considered going with the 2303 FD if this doesn't work and I can't find an older higher level FD that will work. Actually, I bet that a new 2303 front derailleur probably works better than an older higher level FD if I have to go back more than say 15 years or so, just due to the trickle down of new designs/tech.