Front shifter capacity - how flexible?

[KneesUp]

I had a cunning plan. My 'road' bike has a tightly spaced cassette so I can fine tune the gears easily (plus it was in the parts box ... ) and a front triple so I can use it as three 'blocks' if you like - one for hilly bits, one for flat bits, and one for downhill bits.

Unfortunately it's a tad highly geared for when my spindly legs and asthmatic lungs meet long hills, but the inner ring could be smaller (I've 52/42/30 on at the moment) This would though take my FD over it's stated limit (22 teeth) though.

Anyway - to the question - does anyone have any experience of using a triple FD over it's limit. It's a Shimano 105 - I *think* it's is a 5504 series, but I can't check at the moment. I was thinking of going to 52/42/24. I don't want to buy a chaninring to find I can't shift to it. I use down tube shifters so there will be no issue with indexing though.

(I know I will probably have to change the RD as well, but I have a medium cage and a long cage in the parts box already)

 

[raleighnut]

It's not so much a difference in 'capacity' with a front mech, more a matter of height. The chain won't clear the back of the arm unless you reduce the biggest sprocket too.

Easiest way would be a Deore with a 48 or 46 large ring IMO.

 

[KneesUp]

It's not so much a difference in 'capacity' with a front mech, more a matter of height. The chain won't clear the back of the arm unless you reduce the biggest sprocket too.

Easiest way would be a Deore with a 48 or 46 large ring IMO.

Hadn't thought of the clearance issues. Because all my bikes are built out of bits from here there and everywhere, this one has a Campag crankset on it, as it did when I bought the frame from the much missed @vernon. This means the outer rings are more expensive (i.e. Spa don't do 135mm bcd in their own brand) so I was hoping to avoid changing them

 

[the snail]

I think there are a few potential issues, chain rubbing on the bottom of the cage, mech hitting the chainstays if you move it down, or not clearing the big ring. My 5703 setup works with 26T chainring, but with 50T big ring, and changing to small ring is a bit iffy (chain came off the other day). Think you might struggle with 52T/24. I just bought a 26T from Spa and hoped for the best as it was only a tenner. Might be worth taking a punt on 28 or 26, and maybe adding a couple of teeth on the cassette. New chainset would be better though, who needs 52/11 ffs?

 

[I like Skol]

Probably easier and more reliable/usable to do something with the cassette at the back end? It doesn't sound like you are a finely honed pro-rider so would you really be hindered by riding something with a bit more spread?

 

[KneesUp]

Probably easier and more reliable/usable to do something with the cassette at the back end? It doesn't sound like you are a finely honed pro-rider so would you really be hindered by riding something with a bit more spread?

Well no ... but as I said, this cassette had the virtue of being right there in the box of bits in the shed, so I had to justify its existence by using it for something Also I've already shortened the chain too much so I'd have to swap that as well, and I'm lazy

(you're right by the way)

 

[Ajax Bay]

does anyone have any experience of using a triple FD over it's limit. It's a Shimano 105 - I *think* it's is a 5504 series, but I can't check at the moment. I was thinking of going to 52/42/24

Well I'm using the same FD5503 on a 52-42-30. But for the Mille Pennines I replaced the small (30t) with a 28t and the shifting was not as good but worked. And paired with a 12-30 I got up Hardknott Pass and Rosedale Chimney (25" gear length). I think you would find 24t generates several of the issues discussed upthread (eg @the snail 's list).
I reiterate what others have said: change your cassette and accept the wider gap between gear ratios. The RD will handle a 30t without complaint; just don't do small-small (you'll soon hear if you do).

 

[Alan O]

Not sure it's of any use, but I've just checked my triple FD, an "Exage Country". I'm using a 48/38/28, and just by eyeballing it I don't think I'd have clearance to go much below 28 - to 26 maybe, but I suspect a 24 might be too much even with my 48 top.

 

[KneesUp]

I've got 48/38/28 on my MTB-utility-tourer conversion thing - that still uses a Suntour XC-T triple from 1991. If it ain't broke, and so on. I've also used the same Suntour mech on a 42/32/22 just by moving it lower on the frame. The key thing, as @raleighnut says, is the difference in height of the chain. I've adjusted the 105 triple as low as I can get away with (you hear it tinkle on the outer ring if you put a lot of power through on the middle ring as the frame flex makes the teeth touch it, so it's too low really) and when it's on the small ring there is not a great deal of clearance between the chain and the bottom of the guide.

I do have another 48/38/28 crankset in the shed, but it's Shimano, and the BB in this frame is Campag, which as I discovered is a different size square taper, and I don't have a Campag BB removal tool.

Looks like I'd better order a new chain and a cassette.

 

[velovoice]

Well I'm using the same FD5503 on a 52-42-30. But for the Mille Pennines I replaced the small (30t) with a 28t and the shifting was not as good but worked. And paired with a 12-30 I got up Hardknott Pass and Rosedale Chimney (25" gear length). I think you would find 24t generates several of the issues discussed upthread (eg @the snail 's list).
I reiterate what others have said: change your cassette and accept the wider gap between gear ratios. The RD will handle a 30t without complaint; just don't do small-small (you'll soon hear if you do).

I have 52/39/28 plus 11-36. Takes a bit of double-de-clutching style shifting from granny to middle, but I've toured in all terrains, fully loaded and not. Pretty happy with it. Oh and it's Shimano FD and RD but TA Specialties crankset.

 

[andrew_s]

The problems with using a triple front mech past its capacity are ...
a) dragging the chain across the bottom end of the cage when using the smaller rear sprockets
b) a difficult change back up to the middle ring due to the increased distance between the top of the inner ring and where the cage is pushing the chain across. You could end up changing straight over the middle onto the outer.

 

[Ajax Bay]

I have 52/39/28 plus 11-36. Takes a bit of double-de-clutching style shifting from granny to middle, but I've toured in all terrains, fully loaded and not. Pretty happy with it. Oh and it's Shimano FD and RD

That implies the capacity spec of your RD is 49 or close. What make/model is it? Does the guide pulley not interfere with the 36t large sprocket?

 

[byegad]

I ran 55-40-24 to 11-34 on my QNT recumbent trike. It would happily run any combination of front and rear sprockets. The difference between 55-34 and 24-11 makes a tooth difference of 54 and the long reach shimano rear mech coped with it admirably.

Before you object quoting 'crossover' remember it had 2.75 standard chains on it and crossover is irrelevant when the chain runs through a 'mid run' sprocket between front and rear.

 

[velovoice]

That implies the capacity spec of your RD is 49 or close. What make/model is it? Does the guide pulley not interfere with the 36t large sprocket?

RD is this one*.
Works fine with 10-spd cassette.
No problems with 36t sprocket, on granny or middle chainring.
Only compromise is the different way I have to shift from granny to middle (middle to granny is fine). Full story on my blog if you want all the gory details.

*Based on my experiences, Paul Smith (ex-Corridori, ex-Enigma, currently at C&N Cycles in Redhill) recommends this RD to many of his customers. He's quite an expert in "hybrid" drivetrains, i.e. mix and match not all matchy groupset - this on his blog explains the challenges.

 

[Ajax Bay]

How many teeth on the 'mid-run' sprocket? The vertical angle of the chain comes into play, I think. Cross-chaining is an entirely different issue (which may affect, but not much the utility of some chainwheel/sprocket combinations. My comment on the small-small was to do with RD chain wrap capacity: on the OP's RD, if the cahin will go round large/large then the RD will not wrap sufficiently for small/small and the return chain run interferes (noisily) with the cage. This is useful in the dark when you cannot see 'where' you are, gear-wise. No problem: just change into the middle chainring.