Front derailleur for 24/34/40 ?

[zoxed]

As I use short cranks I have corresponding small front chainrings. Although the 40T outer may be a problem my main problem is with the small 6T step 34->40. The current front derailleur just about manages, but often throws the chain off.
I see the problem is the bulge in the inside to the cage designed to help the chain up, but this is usually optimised for >10T.
Does anyone know of a front mech. that can handle my setup, either with the correctly placed bulge, or with straight plates that do not care about the size of the jumps ? (chainline is road triple: 47.5)
TIA, Simon

[freeflow]

How opportune. I spent yesterday afternoon working through gearing options for a new frame I'm having built. There is an interesting article on STI shifting with a Gilles Betoud(?) triple chainset (can't find article now) and how this chainset wasn't suited to Shimano STI because it didn't have the ramps and pins needed to complete the shift. At the end of the article it was recommended that for a triple Giles Bertoud chainset with Shimano STI then a Shimano CX double front derailluer should be considered.

The rationale in the article was that shimano STI make 'bad' shifts as they only move the chain far enough to be picked up by the ramps and pins which then complete the shift. This is to synchronise with the differently shaped teeth at certain points which help to make the shift 'slicker'.

It might be worth a look at a CX shifter.


I'll try looking for the article again when I'm at home.

[zoxed]

It might be worth a look at a CX shifter.

Thanks for your reply: in my Googling the CX70 was one that I found, but the specs are 46-52 top and 2x. But maybe it would work for me ?

[freeflow]

Ha. I'm definitely going senile. Here's the article

http://janheine.wordpress.com/2013/03/2 ... i-triples/

[Valbrona]

You might just have to fit a larger outer chainring. I guess you are using Shimano, but with Campagnolo I have found they need at least an 8t gap between chainrings to work properly.

And also, with very small outer chainrings it can be difficult getting the FD low enough down the seat tube ... and you can get lots of chain slap (against the chainstay).

Interlock Racing Design do an Alpina Front derailleur designed to work with STI levers. Its design is said to be optimized for use with small chainrings and might be worth a try.

What chainset are you using anyway?

[freeflow]

I'm currently using a 6700 shifter to do 52/39/24 so there can be a lot of leeway in setup provided you don't mid spending a little time tweaking. I'm currenlty trying to decide to go with a smaller triple 44 or 46/34/22 ish or with a 12 -29 cassette or to take the plunge an go for a double 46/24 is with a 12-32 (or larger) cassette.

Based on my legs I don't really need anything bigger than around 90-95 inch gear but might benefit from going a little lower than 24/28. As I want to use road STI that's got me also scratching my head about which front deraillier I'd use. The larger cassette gives more even steps across the gear range (which is OK given I usualy shift 2 or 3 gears at a time). This thinking is for mainly Audax riding.

I'll be interested to hear how you get on.

[zoxed]

You might just have to fit a larger outer chainring.

I guess you are using Shimano

Yes: no model#, just '9 speed', but shifters and rear are SRAM.

And also, with very small outer chainrings it can be difficult getting the FD low enough down the seat tube

I was hoping a top mount SRAM may help there ?

Interlock Racing Design do an Alpina Front derailleur

Thanks, but their website showing the current model only recommends down to 48

What chainset are you using anyway?

Thorn: http://www.sjscycles.co.uk/thorn-110-74 ... -prod1673/

Further note: I am not worried and indexing, shifting under load, ramps... I just want it to change OK as I spend 98% time only on the middle ring !

[CREPELLO]

Unless somebody here has made an identical set up to yours, there is going to be a lot of speculation as to what might work. So here's some more ...

Perhaps try a Campag double mech and bolt the cable on the other side of the cable clamp bolt. I've done this (but with a triple FD and 48/38/28 CS) in conjunction with Shimano STI and can confirm that it works very well.

Consider a more conventional chain ring arrangement, but alter the cassette ratios by making a hybrid cassette from two Deore/Tiagra grade cassettes.

There are Shimano 42/32/22 chainsets with compatible FD's (you could re-clamp the cable just like the Campag mech). Problem is the FD will be for MTB chainline, which only adds complications.

I'd give the Campag mech a go myself.

[zoxed]

Ha. I'm definitely going senile. Here's the article
http://janheine.wordpress.com/2013/03/2 ... i-triples/

Thanks: main points for me are that it is flat sided, and "The CX-70 derailleur is a great choice, whether you run a double or a triple."

[gaz]

30-34-38T with Suntour Superbe Pro double. I've used Shimano 105 (1050) and Dura-Ace (7400/7401) with equal success on this and similar set ups including 28-36-40T and IIRC 24-36-39T. Friction shifting and very briefly with RSX STI but that only worked reluctantly.

All of those are late 80's early 90's road double mechs.

[Tigerbiten]

All of those are late 80's early 90's road double mechs.

I agree.
My thinking is you need a mech which is able to half step.
Hence late 80's early 90's road double mechs with friction shifters or take a dremel/saw/file to a modern mech to alter the shape of the cage.

[gaz]

We have a half step triple thread from which you can extract model numbers and further recommendations.

There's unlikely to be anything current but it could help narrow down the cycle jumble and ebay searches.

[JohnW]

I don't know how much this helps, because it's not exactly the same, but I have a 30-40-48 triple on one of my bikes, which is 8T difference between middle and big ring - 2 more than the OP's question.

I have an Ultegra front changer and I have no problems with it - I built the bike up in 2006, so there's been chance for any gremlins to show themselves.

I do, however, continue to use friction down-tube gear levers, and that may be be factor - the cage on the front changer goes where I decide, and not where a pro-loaded spring sends it.

[Pandaz]

An older xtr from late 90's should work.

[zoxed]

Thanks for all the tips: Googling further I see:
- Shimano CX seems to have a lump in it, suggesting a minimum ring difference ?
- all the old models I have looked at (suggested on the thread) seem to have a small diameter than my 32mm tube has: I guess too-large can be shimmed, but too small is difficult !: maybe a 32mm braze-on adapter with an old, braze-on, model would work ?
- I measured the chainline (difficult) at 45, although research suggests it is probably 47.5, so not sure if a CX70 rated at 43.5 would go far enough ?!