front deraileur dilemma

[chrisd]

Decided to switch to a 42 big ring from a 44 on a Ritchey Logic triple CS (44/34/26) on my Rambouillet and tried a Skeleton Key FD but can't shift to the granny. My old shimano FD tail barely cleared the chainstay with the 44 so any older derailers won't work. Riv says the Skeleton works on triples but it's probably something to do with geo on the current models.Need a short cage FD. Thought of a mountain FD.  My brifters are old Campy so don't have to worry about indexing. Any suggestions?

[Joe Bernard]

Two teeth smaller shouldn't require a repositioning of the mech you were using. Did you have a problem with it? 

[Bill Schairer]

I'm not sure I understand the "so any older derailers won't work" comment.  My 2014 Atlantis with a Suntour Vx (from the 70's?) front derailleur shifts a 42/34/19 flawlessly.  I do use a chain catcher to prevent dropping the chain going to the 19.

Bill S

San Diego

[Steven Sweedler]

Bill what crank are you using that allows a 19 T and who makes the 19 T.  Thanks, Steve 

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Steven Sweedler
Plymouth, New Hampshire

[Patrick Moore]

I shift between a 42 t and a 28 t Sugino ring on a Ritchey Logic subcompact double with guard in place of the outer ring using a 740x fd and it works just fine. I installed it so that the aft-bottom of the cage barely clears the stay; this means that the cage sits rather high above the 42; but it still shifts as well as any other fd I've used.

So, suggestion: old road front derailleur.

[Bill Lindsay]

I concur that the skeleton key front derailer turns out to be a "high Q factor" or "large front chain line" model.  When used on a skinny tire road bike, with a narrower Q factor crankset, it doesn't reach.  

Still, I really liked the cage size and shape, so I went ahead and made my own eccentric spacer to pull it inboard, and now it shifts my narrow-Q-factor triple just fine.  

Here's the plastic raw material I used: https://www.flickr.com/photos/45758191@N04/52444537055/

Here's what the finished spacer looks like: https://www.flickr.com/photos/45758191@N04/52444371359

Here's what it looks like with the FD clamped around it:  https://www.flickr.com/photos/45758191@N04/52445653361

Here's a link to the entire album, which has some more shots of my setup on my small lathe:  https://www.flickr.com/photos/45758191@N04/albums/72177720303067081/with/52445653361/

Bill Lindsay

El Cerrito, CA

On Sunday, November 27, 2022 at 2:50:52 PM UTC-8 chrisd wrote:

[ascpgh]

When I converted my TA Zephyr to compact double (46/34) on my Rambouillet I switched to a shorter BB spindle that ostensibly set up the problem you described more than the reduced tooth count of your 42. RIng position means more on my Ram than their diameter. Mine, in a close double on a short spindle to reduce the Q-factor by the increased clearance of the big ring teeth and the right chain stay, is shifted with an improbable Mavic 860. A road racing pro's FD suited for large rings and a max range of 20 teeth.

I agree that on "full sized" chainring combinations, the tail of the FD cage has more involvement in physically engaging the chain during shifts but the ring size disparities mean nothing if the swing of the cage doesn't reach the rings as they are in relation to the seat tube because of the narrow Q-factor your bike has. I have a Coast 650B rando with many cues from my Rambouillet that has RH cranks (low Q) with 46/30 rings and the best suited FD when building up the bike came not off the shelf at the bike shop but from my drawer of curated models from the past. A Suntour Superbe Pro clearly intended for 53 and 42 adjusted nicely to the rings and has the operating range to move the cain to the inner position without concern for dropping the chain operated with bar end shifters instead of indexed.

The other thing not yet mentioned is the RIvendell BB drop (amount below the line from front hub to rear hub of the BB). Greater BB drop closes the angle between the seat tube and chain stay, making the interference of the FD cage's tail and the chain stay sooner than a bike with less BB drop. 

Andy Cheatham

[Bill Schairer]

Steven,

I am using a Silver crank in conjunction with a Mountain Tamer (https://abundantadventures.com/mt_triple.html), which can be used with any crank without modification with a 74bcd that requires chainring spacers.  I have used this set-up on two different tours (about 400 miles on GDMBR, 2800 miles riding to Alaska) without any issues at all, which I mention as evidence of real world practicality/reliability.  I don't know, availability may be an issue?

For kicks, I did experiment briefly with the Mountain Tamer in quad mode.  It did work but I abandoned that set-up as too fiddly (as I recall, I had to modify a Silver bar-end shifter and the cage of a Suntour Cyclone derailleur to just barely be able to shift all 4 rings) and it was confusing. Now, as I write this, having a 26t between the 34 and 19 on the last tour almost makes me think the quad might have been worth it?  The 34/19 shift always worked both ways but I didn't really like the jump. Then again, I really did need that 19/36 combo, not just once or twice.  Around town, as a quad it was total overkill.

I'm one who loves playing with my gearing and hates experimenting with handlebars.

Bill S 

San Diego

[David Person]

I have a 44/28 setup on my Hillborne with a Shimano 105 (FD-5700) front derailleur.  I can't set it at the recommended height (1-3mm clearance above large chainring) due to the rear of the cage hitting the chainstay.  It shifts fine without dropping the chain off the large chainring.  In fact, I watched a Park Tool video on proper set up of a front derailleur and they state that if the gap between the ft derailleur and large chainring is more than recommended it can cause the chain to be dropped outboard.  Interesting, when I set up my Disc Trucker with a 42/28 and CX70 front derailleur, I was able to set the hight as recommended and it caused problems with the chan being dropped outboard.  When I raised the derailleur to create a larger gap to the chainring, it shift perfectly.

[Steven Sweedler]

Thanks Bill, the mountain tamer were popular around here years ago, even a few quads, I am satisfied with my 20 T (58 bcd) to a 34, it usually gets me up the hill. 

Steve

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[Nick Payne]

I routinely use 2x MTB FDs (for preference Deore XT M786 2x10) with two- chainring setups and road chainline where the large ring is between 36 and 42 tooth. I have those in use with Shimano 10- and 11-speed indexed road shifters, and also with SRAM 11-speed road shifters. The front shifting works perfectly. For example, here's one on my Appaloosa which has 38/26 chainrings.

You can also shorten a derailleur cage if it fouls the chainstay. Here's a SRAM Red eTap FD that I wanted to use with 34/22 chainrings, so I cut off the bottom of the derailleur cage and bolted on the end of the cage from an old clapped-out FD across the inner and outer plates of the cage. That one works perfectly in it's modified state across chainrings about 20t smaller than the FD was designed for.

Nick

[Justus G]

While lots of setups work just fine with minor compromises, I have found there is an optimal FD setup for 42/44 (even 46) big ring compact gearing if we are talking 8/9 speed triple compatible or similar as a baseline.

HyperDriveC compatible old Shimano FDs in the form of XT M737 and LX M563 (or similar) are short cage FDs so they clear the chain stays and also allows you to generally get your FD at the right height above the big ring.

All threads benefit from pics so here is one of my Riv's with a hand sanded silver (not by me) NOS LX M563 FD on my 24/34/46t triple:

[Patrick Moore]

That front derailleur does have an exalted height above the big ring but I gather that it shifts fine. I've left an LX fd in place when I removed the out 46 t ring and replaced the middle 36 with a 38; the inner 24 remained. It must have sat as high over the (now) outer 38 as yours above your outer ring. I just adjusted the travel limit screw. It shifted as well between the 38 and 24 as it did before between the 36 and the 24.

My current DA 7402 (I think it's "...02") sits high enough to just clear a bash guard sized to hide a 46 t ring -- ie about the size of a 48 or so -- so the cage sits high indeed over the 42 t big ring. It still shifts wholly unexceptionally.