9-speed triple front mech for outer 48t chainring?

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toontra
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Re: 3-speed 9-speed triple front mech for outer 48t chainring?

Postby toontra » 4 Jan 2021, 6:19pm

Another candidate - Deore XT FD-M770

Seems perfect. Might even have found one!

Brucey
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Re: 3-speed 9-speed triple front mech for outer 48t chainring?

Postby Brucey » 4 Jan 2021, 6:27pm

one further comment is that top swing mechs tend only to work on a MTB chainline. I guess I assumed that as it is a MTB frameset you would be running a MTB chainline, but a 28-38-48 chainset for touring might be run at a narrower chainline on a steel-framed MTB (that is how I used to do it, anyway). Top swing mechs tend not to swing inwards as far as bottom swing mechs, by enough to make a difference if you are running a narrower chainline.

When 7/8s was the thing, shimano supported (not with every FD admittedly) both 47.5mm and 50mm chainlines for MTB triples. But when 9s came in, I think they (nearly?) all went to 50mm only.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

nsew
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Re: 3-speed 9-speed triple front mech for outer 48t chainring?

Postby nsew » 4 Jan 2021, 6:30pm

slowster wrote:
nsew wrote:The Shimano FD-CX70 ticks a lot of your boxes and is known to shift awkward triple set ups. I had no interference with bottle cage bosses however that was a bottom pull.

From https://www.renehersecycles.com/trouble-with-sti-triples/:

Addition (3/7/2015): A reader pointed out that the “top pull” version of the CX-70 derailleur does not swing far enough to shift a triple crank. Only the standard “bottom pull” version works for triples.


Right, thanks for that. I now recall a mtb forum discussion on that point, there’s less radius on the top pull. Someone came up with an unsightly mod using a dremel. The article and comments made good reading.

gregoryoftours
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Re: 3-speed 9-speed triple front mech for outer 48t chainring?

Postby gregoryoftours » 4 Jan 2021, 11:30pm

What brand and model of chainset are you using? If you were prepared to use a more standard Shimano 9sp 48/36/26 chainset eg T3010 your choice of front mech would be simpler. Personally if possible I'd also go for a dual pull bottom swing mech with something like that, eg fd-m761a. The pivots last longer and the derailleur also doesn't develop rattle as it wears like a top swing will. I happen to also have an old clockwork with a 28.6 seat tube. I use that mech with top cable pull routing and an old 9sp lx chainset on the bike. It's not exactly period correct but works well.
IMG_20210104_231238_HHT.jpg
It's a 44/32/22 on the clockwork but the same model also works fine with a 48/36/26 on another bike (on this frame it's bottom cable pull routed, it's a spoke in the background not a top routed cable!)
IMG_20210104_231938.jpg

gregoryoftours
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Re: 3-speed 9-speed triple front mech for outer 48t chainring?

Postby gregoryoftours » 4 Jan 2021, 11:39pm

By the way, if anybody ever needs an eccentric shim 31.8/34.9 even though they aren't sold as such these cheapos seem like they might be just that -
Bicycle Front Derailleur Ring Adapter Convert 34.9mm to 31.8mm MTB Mountain Bike
https://www.aliexpress.com/item/32913272103.html
If they are then it's quite a saving over the price of better quality ones sold in the UK.

toontra
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Location: London

Re: 3-speed 9-speed triple front mech for outer 48t chainring?

Postby toontra » 5 Jan 2021, 10:23am

Thanks for the suggestions. I'm planning to build it up with an Alivio T4060 crankset and XT MT800 bottom bracket. On previous Clockworks I've used square tapers and cheapo Stronglight cranks. The reason for the change is so I can swap a 4iiii 105 left crank power meter between 3 of my bikes as they will all have Hollowtech cranksets (and the same length cranks - 175)

This is the bike I (have & hopefully will again) take on foreign tours and training camps, and I've always been curious on power output when doing big climbs in hot climates :D

BTW I've ordered the only new Deore XT FD-M770 front mech I could locate in the UK (and it's just down the road from me in London)!

Nigel
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Re: 3-speed 9-speed triple front mech for outer 48t chainring?

Postby Nigel » 5 Jan 2021, 12:00pm

Brucey wrote:one further comment is that top swing mechs tend only to work on a MTB chainline. I guess I assumed that as it is a MTB frameset you would be running a MTB chainline, but a 28-38-48 chainset for touring might be run at a narrower chainline on a steel-framed MTB (that is how I used to do it, anyway). Top swing mechs tend not to swing inwards as far as bottom swing mechs, by enough to make a difference if you are running a narrower chainline.


That's the point I was raising earlier about using an eccentric shim on a steel framed 1990's MTB frame with a narrower chain-line. The eccentric shim moves the mech so it sits correctly over the narrower chain-line.

Brucey
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Re: 3-speed 9-speed triple front mech for outer 48t chainring?

Postby Brucey » 5 Jan 2021, 12:17pm

Nigel wrote:...That's the point I was raising earlier about using an eccentric shim on a steel framed 1990's MTB frame with a narrower chain-line. The eccentric shim moves the mech so it sits correctly over the narrower chain-line.


eccentric shims can help but mainly if you are pretty much forced to use a mech that uses a shim anyway; IME it is unusual for a top swing mech to allow the cage any further inwards than the RH edge of the shim, so you are little better off using a large clamp mech with an eccentric shim than you would be with a mech which used the correct clamp size for the seat tube to start with. IME a bottom swing mech can be better at tight chainlines than a top swing mech is (with or without a shim). For some reason I have had good results with braze-on mechs (with band-on adaptors where necessary) when setting up road triples with tight chainlines.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

toontra
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Re: 3-speed 9-speed triple front mech for outer 48t chainring?

Postby toontra » 5 Jan 2021, 12:20pm

Thanks all for the advice and suggestions. I'll update to say if it works.

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Sweep
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Re: 3-speed 9-speed triple front mech for outer 48t chainring?

Postby Sweep » 6 Jan 2021, 2:28pm

Brucey wrote: using a high band usually means little more than losing the seat tube bottle bosses.

cheers

If I've understood what you mean correctly, that the clamp gets in the way of the bottle cage, I get round this by just putting a small thickish washer on top of the boss, which raises the bottle cage clear of the clamp. At least on my bikes. I find those Presta valve knurled things ideal.

Have never found that the clamp actually covers the bosses, just obstructs the normal seating of the bottle cage.

apologies if I have misunderstood something.
Sweep

mcshroom
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Re: 3-speed 9-speed triple front mech for outer 48t chainring?

Postby mcshroom » 8 Jan 2021, 3:14pm

Sweep wrote:
Brucey wrote: using a high band usually means little more than losing the seat tube bottle bosses.

cheers

If I've understood what you mean correctly, that the clamp gets in the way of the bottle cage, I get round this by just putting a small thickish washer on top of the boss, which raises the bottle cage clear of the clamp. At least on my bikes. I find those Presta valve knurled things ideal.

Have never found that the clamp actually covers the bosses, just obstructs the normal seating of the bottle cage.

apologies if I have misunderstood something.


That works fine as long as the manufacturer didn't do something daft, like line up the bottom bottle boss exactly where the derailleur clamp wants to go (Thank you Claud Butler :roll: ). To be fair, they did spec the bike with a top swing derailleur from new, but it did limit options when I converted it to drops.

Brucey
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Re: 3-speed 9-speed triple front mech for outer 48t chainring?

Postby Brucey » 8 Jan 2021, 3:20pm

mcshroom wrote:...That works fine as long as the manufacturer didn't do something daft, like line up the bottom bottle boss exactly where the derailleur clamp wants to go (Thank you Claud Butler :roll: ).


I have also encountered the exact same problem (hence my comment of 'usually' rather than 'always'). In one case I lucked out and found I was able to fit a FD with a shaped steel clamp band over the lower bottle boss and it worked out OK. But I would much rather they had put the bottle bosses higher up to start with; the frame was not that small and they could easily have been an inch higher....

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

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Sweep
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Re: 3-speed 9-speed triple front mech for outer 48t chainring?

Postby Sweep » 8 Jan 2021, 4:40pm

Brucey wrote:
mcshroom wrote:...That works fine as long as the manufacturer didn't do something daft, like line up the bottom bottle boss exactly where the derailleur clamp wants to go (Thank you Claud Butler :roll: ).


I have also encountered the exact same problem (hence my comment of 'usually' rather than 'always'). I
cheers

should have known you'd thought of everything brucey :0
all the best

clearly 1990s Ridgeback thought things through better - I have two different ones - both fine.
Sweep