Best front derailleur for half step plus granny

In article ,
Russell Seaton wrote:
I am transferring my touring bike parts to a new frame. The new frame
needs a 1.25" clamp on front derailleur. So my old 1991 Shimano Deore
DX half step specific 1.125" clamp on front derailleur won't fit.

My chainrings are 48-45-20. Half step plus granny. Rear cogs will be
9 speed 12-34 cassette.

1. Which current front derailleur will best handle the 3 tooth
difference between the 48 and 45 chainrings and still allow the use of
the 20 tooth granny with the largest 4 or 5 rear cogs without dragging
the chain on the derailleur cage?

2. I know a double front derailleur will handle the half step very
well. But how would it work with the 28 tooth difference in
chainrings?

3. Is there any way to change clamps on my old front derailleur? Can
I buy any cheap Shimano front derailleur and easily change clamps?

I feel your pain. If you can't find something from, say, Rivendell, then
my recommendation is to get a road front that doesn't have the deep inner
plate, and extend the plates toward the rear. Most derailleurs have steel
plates (IIRC) so it's fairly easy to braze or weld extensions.

There will probably be some that argue against the 1/2+Gr arrangement,
but I'm with you -- there are nice things about this arrangement.

Good luck -- and let us know how it works out!

-frank
--

Russell Seaton wrote:

I am transferring my touring bike parts to a new frame. The new frame
needs a 1.25" clamp on front derailleur. So my old 1991 Shimano Deore
DX half step specific 1.125" clamp on front derailleur won't fit.

This, I think, is what really screws you when it comes to a half-step.

My chainrings are 48-45-20. Half step plus granny. Rear cogs will be
9 speed 12-34 cassette.

1. Which current front derailleur will best handle the 3 tooth
difference between the 48 and 45 chainrings and still allow the use of
the 20 tooth granny with the largest 4 or 5 rear cogs without dragging
the chain on the derailleur cage?

2. I know a double front derailleur will handle the half step very
well. But how would it work with the 28 tooth difference in
chainrings?

If it weren't for the clamp issue, these work great just like your Deore DX:

http://cgi.ebay.com/ws/eBayISAPI.dll...m=3685486 553
http://cgi.ebay.com/ws/eBayISAPI.dll...m=3685712 205

3. Is there any way to change clamps on my old front derailleur? Can
I buy any cheap Shimano front derailleur and easily change clamps?

I doubt it. Many of the f-ders have half the clamp as part of the derailleur itself. You could
look for the model of Suntour Cyclone f-der with the totally removable clamp. Maybe you could
replace it with a custom clamp. I don't know if I've ever seen a 31.8 Suntour Cyclone. All I've
seen were 28.6. My Cyclone is not the removable clamp model.

Let me know if you have trouble. I have a cheapo Suntour front der that I bent (modified) the cage
on that I would sell you if you got desparate. It would probably work for you. It has a 31.8
clamp. I use it with a 46-42-26 front. It works, but is not perfect. (This is not the Cyclone.)

(Russell Seaton) wrote:
My chainrings are 48-45-20. Half step plus granny. Rear cogs will be
9 speed 12-34 cassette.

1. Which current front derailleur will best handle the 3 tooth
difference between the 48 and 45 chainrings and still allow the use of
the 20 tooth granny with the largest 4 or 5 rear cogs without dragging
the chain on the derailleur cage?

2. I know a double front derailleur will handle the half step very
well. But how would it work with the 28 tooth difference in
chainrings?

Help me out here. I thought the biggest difference between a double
and triple front changer was the range of motion (side to side)
available. That is to say, I don't think there would be any
difference between a front derailleur for a half-step granny and any
other triple set-up. Am I mistaken?

It's been a few years since I ran a half-step granny, but doesn't the
half-step make things better, not harder? I mean, with only a 3 (I
used to run a 4 t diff back in the day), you can mount the changer
lower and closer to the center ring without the outer cage hitting the
the outer ring like you would if you had a 10 t or 12t diff, no?




-- Dave
==============================================
"It is impossible, or not easy, to do noble acts
without the proper equipment."
Aristotle, Politics, 1323a-b, trans Jowett
==============================================

Russell Seaton wrote:
=20
My chainrings are 48-45-20. Half step plus granny. Rear cogs will be
9 speed 12-34 cassette.

1. Which current front derailleur will best handle the 3 tooth
difference between the 48 and 45 chainrings and still allow the use of
the 20 tooth granny with the largest 4 or 5 rear cogs without dragging
the chain on the derailleur cage?

Virtually any modern "double" type front derailer will work for=20
half-step-plus-granny.

2. I know a double front derailleur will handle the half step very
well. But how would it work with the 28 tooth difference in
chainrings?

This may require some experimentation, may also require some surgery to=20
the cage.

See: http://sheldonbrown.com/derailer-adjustment

An anomymous poster asked:

Help me out here. I thought the biggest difference between a double
and triple front changer was the range of motion (side to side)
available. That is to say, I don't think there would be any
difference between a front derailleur for a half-step granny and any
other triple set-up. Am I mistaken?

Yes, you are.
=20
It's been a few years since I ran a half-step granny, but doesn't the
half-step make things better, not harder? I mean, with only a 3 (I
used to run a 4 t diff back in the day), you can mount the changer
lower and closer to the center ring without the outer cage hitting the
the outer ring like you would if you had a 10 t or 12t diff, no?

Modern "triple" front derailers have an inner cage plate that hangs down =

much lower than the outer one. This is to facilitate the upshift from=20
the smallest ring to the middle.

They also generally have a more 3-dimensional outer cage plate to reduce =

rubbing when clueless riders cross chain the small/small combinations.

Sheldon "There Is A Difference" Brown
+---------------------------------------------+
| If your bike has drop handlebars, but you |
| rarely or never ride on the drops, it=92s a |
| sure sign that your bike is not properly |
| fitted or is not properly adjusted! |
| See: http://sheldonbrown.com/handsup |
+---------------------------------------------+
Harris Cyclery, West Newton, Massachusetts
Phone 617-244-9772 FAX 617-244-1041
http://harriscyclery.com
Hard-to-find parts shipped Worldwide
http://captainbike.com http://sheldonbrown.com

I asked:
Help me out here. I thought the biggest difference between a double
and triple front changer was the range of motion (side to side)
available. That is to say, I don't think there would be any
difference between a front derailleur for a half-step granny and any
other triple set-up. Am I mistaken?

Sheldon replied:
Yes, you are.

So, do all (most) modern double and triple FDs have the same range of
motion side to side? I would have expected that some double FDs
wouldn't have enough travel for a triple.

Sheldon continues:
Modern "triple" front derailers have an inner cage plate that hangs down
much lower than the outer one. This is to facilitate the upshift from
the smallest ring to the middle.

Ah.... so do I understand correctly.... This lower inner cage plate
would become the limiting factor for how low you can mount the FD so
it will clear the middle chain rain when the cage is over the outer
chanring. And given the huge difference in the lower edges of the
inner and outer cage plates, this would leave you with the FD too high
for effective shifting from the outer to middle chain rings. Did I
get that right?


-- Dave
==============================================
"It is impossible, or not easy, to do noble acts
without the proper equipment."
Aristotle, Politics, 1323a-b, trans Jowett
==============================================

Russel and Sheldon, can you guys reconcile the following?

Russell Seaton wrote:
I really need a front derailleur shaped like a triple,
to handle the capacity between the outer and inner chainrings, [snip...]

Sheldon wrote:
Virtually any modern "double" type front derailer will work for
half-step-plus-granny.

Russell, I'm assuming that you are concerned about:
a) the chain draging on the connector bolt that runs between the 2
sides of cage when on the granny or
b) clean shifts from the granny up to the middle

Sheldon, thanks for the clarification in your other post.


-- Dave
==============================================
"It is impossible, or not easy, to do noble acts
without the proper equipment."
Aristotle, Politics, 1323a-b, trans Jowett
==============================================

Jeff Wills wrote:

To the OP: I recall that the Shimano Deore and Deore XT front
derailleurs came in both "half-step" and "alpine" versions in the late
80's. I *think* there was one that featured an endless-band clamp that
was adaptable to 1 1/4" seat tubes. I can't recall if there was one
with *both* a half-step cage *and* an endless band clamp...

Yes (I had the Deore 31.8mm variety on a Cannondale touring bike)
but it looks a lot like a typical road double front derailler.

but I'd
bet that one of the old-guard bike shops could get one from Euro-Asia
if they ever existed. I can't say for sure, though.

(Russell Seaton) wrote:
I know the double front derailleur will shift the half step very well.
But a double front derailleur won't handle the granny worth a darn.
Especially not a 28 tooth difference between outer ring and inner
ring. Dragging on the connector bolt is what I am concerned about.
But I think I have an old Superbe double front derailleur I can fit to
see how badly it drags. I want the biggest 4 or 5 cogs to not drag
when using the inner ring.

You and I might have very different desires for a half-step granny
that are leading to different gearing choices (neither good nor bad).
I suspect that your gearing prefs may be complicating the FD issue
though.

I used to run a 44/40/20 front crank and my old Suntour DL double FD
handled the 20t drop just fine. However, I alway ran this with a 32t
rear cluster and never used (or wanted to use) the granny on anything
smaller than a 28t rear cog. As I contemplate setting up a new
Half-step rig, I'll probably shoot for 42/39/?? to get the 3t diff
with commonly made chain rings.

Note, I don't ride big gears so I can live with smaller outer and
middle chain rings. More to the point, I associate big chain rings
with racing and fast sport riding where shifting performance counts.
For that, I think alpine gearing makes more sense as it favors faster
single rear shifts. For the touring and long-distance riding I like, I
want to find the exact right gear for that long grind into the head
wind. But this is slower speed riding and a result, lower geared than
I think your large chain rings would provide.





-- Dave
==============================================
"It is impossible, or not easy, to do noble acts
without the proper equipment."
Aristotle, Politics, 1323a-b, trans Jowett
==============================================

Jeff Wills wrote:
Benjamin Weiner wrote in message news:40e218f2$1@darkstar...

Yes (I had the Deore 31.8mm variety on a Cannondale touring bike)
but it looks a lot like a typical road double front derailler.

Ah, so... I kind of figured it would be used on a Cannondale. As to
it "looking like a typical road double front derailleur"... whaddaya
wanna bet the cage is longer?

I managed to dig it up, and I think we're both wrong. The cage
is about the same length as a road double, and oddly, the inner
plate is deeper than a road double. It looks similar to the
type of FD that came on early mountain bikes with 48-38-28 rings.

(Russell Seaton) wrote:
You will have a very hard time getting your cassette cogs to work in a
half step pattern if you go with 42-39 chainrings.

Interesting. I'll have re-run my numbers tonight. My first cut at it
showed a perfect interleave with the stock 12-28 7 speed cassettes.
I'll take a second look. Glancing at my numbers, my suggested 42/39
combo isn't very happy as it doesn't give me enough high gear choices.
My prefered choice for a 7-speed cassettes would be a 44/41 and I
think it will work for most common cassettes. But, I can't seem to
find 41t middles for a 110mm bolt pattern.

One of the reasons I am using 48-45 chainrings is because
they work wonderfully with the very common 14-16-18-21-24-28-32 7
speed cassettes.

Where are you finding a 45t middle ring? My current cranks have a
110/74 bolt pattern and 39 is one of the few odd numbered chain rings
I've been able to find (Salsa and Sugino both make 'em).

My low gear on the middle ring will be 45x30 or 45x34, assuming I get
the 9 speed cassette to work. 41 or 36 gear inches. My next lowest
gear on the granny ring would be 20x18. 30 gear inches. I really
need the front derailleur to work with the top 5 cogs on the cassette
without dragging on the connecting bolt.

Hmm.... What I like for loaded touring is to have big enough jump
that I can sit and spin on a granny during a climb and then shift to
the middle to climb out of the saddle (to stretch the legs). When the
jump is just right, this can be done with only a front shift no rear
shifts. For this I only needed the top 2 or 3 rear cogs with my
granny, which resulted in a higher chain line.

I'll look in my notes but I'm pretty certain my old (6 speed) set up
was a 44/40/24. I think I would find your proposed 45 middle to create
too high of a gear, even on the larger rear cogs. That's what I was
trying to say earlier... if you can go lower on your middle, you don't
need to go as far into your rear cassette with your granny.

I'm struggling to see the advantage of a half-step with 9 speeds
though. At that point, doesn't wide range alpine gearing make more
sense with fewer double shifts?


-- Dave
==============================================
"It is impossible, or not easy, to do noble acts
without the proper equipment."
Aristotle, Politics, 1323a-b, trans Jowett
==============================================