masi61

So I'm setting up this really cool women's specific 1883 Cannondale touring triple with interesting, rare ERTO 590 wheels and tires. A worthy project we thought. Everything is great and the bike is just about out the door with Sora 3 x 7 triple seven speed sti brifters. 7 speed rear s.i.s thread on freewheel with Shimano Light Action s.i.s. rear derailleur - a snap - the stuff works beautiful with the new Taya turbo chain. Triple front crank has 94 bcd chainrings in a 30-44-48 sorta halfstep with granny, sorta commuterbike mild gearing. Old friction front derailleur was a SunTour cyclone endless band. I decided to try a Shimano Deore (interestingly it also has Shimano's version of endless band). I went to the bikeshop and got a little nylon spacer for the front derailleur band to bring a 35mm down to a 31.8 mm to match the Cannondale seat-tube. The Deore front derailleur is engraved on the back of the cage "half-step" - interesting - I'm thinking - if anything has a shot of indexing on the first (or second, or third, or fourth ) try, this could be my ticket to precision.
So I set the thing up...I must add that I'm a downtube shifter kind of mechanic, a little too old school I guess. Anyway, setting up the Sora Shifters was much easier than I thought.
The problem is the grinding in the middle chainring mainly,only a few rear cogs are immune. The Sora shifts into 3 positions with very positive CLUNKs (as opposed to the rear where its satiny smooth light action quietness). I'm bidding on some 105 triple 31.8 FD's on ebay right now but I keep losing the auctions.
Can anyway direct me on how to get this funky half step triple crank to index better with the Sora brifter ? Thanks.

TallRider

I think your problem is with the front derailler's cable-pull ratio more than with the chainring sizing. Main issue is that you're using a Shimano off-road front derailler with a road-triple indexed front shifter. As I understand it, Shimano's road-triple front deraillers have a different cable-pull ratio than Shimano's off-road front deraillers. So you'd need a 105 or Sora or Tiagra (etc.) triple-compatible front derailler.
When you're shifting with a double-chainring setup with STI shifters, you can usually get away with whatever front derailler you want. Triples are much more finnicky and usually you'll need a Shimano front derailler designed for triple-STI shifting.

masi61

Thanks for your prompt reply. I was kind of wondering if the cable pull was wrong due to it being a mtb front derailleur. They have a Tiagra 31.8 triple for $34.99 in stock at the LBS down the street and I can get 10% off that - still a little more than I wanted to pay but, OH Well - so maybe I'll go get it today. My friend who is bankrolling the project told me she wants it to work VERY WELL and she said she'll pay me a little more (50 bucks or less she said) for me to just get it dialed in right.
The only concern I have with the Shimano 9 speed road triples is something I read on the specification sheet for the FD-5503,FD-5504 105 triple front derailleur. It reads: "Min. distance between top and intermediate - 10T".
Now since the crank I'm using only has a 4T difference, can I still dial this thing in?
Thanks again Tim for the quick response .

TallRider

I doubt that difference will be a big problem, but it may be. I'd have set it up as a 48/40/30t myself. But the 44 may be the ideal cruising gear...

masi61

I think you're right. Something like a 39, 40 or 42 would be better I think to make the thing a little more versatile. The only 94 bcd chainrings I find on ebay right now are like 44's (which is already on there) or like 32's.

TallRider

On the other hand, lots of older touring bikes with triple cranks had 52/48/30 chainrings, the idea being that the middle chainring was what you'd use most of the time and the granny was a bailout gear. I still don't think it's a great setup, but the 48/44/30 is kinda similar so it does have precedent.

I'd not realized how difficult it's getting to find 94mm bcd 5-bolt chainrings. It might be easier/cheaper to get a used old MTB setup with 110mm bolt pattern and 46/36/26 chainrings.

Retro Grouch 

Yeah, but back in those days front derailleurs didn't have that deep inner blade like modern triple front derailleurs do. I think that the issue with the 10t minimum difference is that the inner blade might rub the middle chainring.

masi61

That's partly what I was thinking, thus the attempt at making the Deore FD work. I fiddled and fiddled with the Deore this morning and there are a lot of issues but there is a sweet spot where you can get into a lot of gears without much rubbing. I'm going to ask my friend to try out the Deore FD and see if she can live with it.

TallRider

This is an example of why I really prefer Campy's non-indexed 13-increment approach to front shifting with brifters. Allows you to trim the front derailler cage and not worry about compatibility issues.