Best front derailleur for half step plus granny

(Russell Seaton) said:

I've run the numbers on my spreadsheet using my existing
14-16-18-21-24-28-34 7 speed cassette and a 42-39 did not
work well. 42-40 worked better. The best chainring setup
I've found with the above 7 speed setup is the 48-45 half
step. The 42-40 setup just did not produce enough jump
between successive gears. Your 12-28 7 speed cassette is
the same as the above cassette except you have a 12 instead
of a 34 or 32.

Couple of things, including a retraction/correction.

1) I was able to dig out the specs from my old set up. It
was (to my astonishment) a 50/46/24, very close to your
preferred 48/45. I musta had young legs once. Note: I
used it with a 13-32 6-speed cassette.

2) I'm not seeing the pit falls of the 42/39 yet, other than
the really low gearing. My casual review of the gear
charts (generated from Sheldon's very cool site) suggest
that any 3 tooth jump on the chain rings gets you really
close with most off the shelf cassettes. More important I
would think, is whether or not the general size of the
chain rings is getting the basic range of gears desired.
I think your 48/45 is probably better in this regard.

3) I'm still getting my head around your desire for running
a 24t chain ring with 24 - 18 cogs. My gear charts
(again, taken from Sheldon's site) indicate this is in
the gear inch range of 26 to 39 inches or so. It looks
to me that this run of gears is available with a 36t
chain ring on 34 - 28t cogs. If you want something close
to a steady set of step (full, half or what have you)
from a 20 inch gear up to 100 inch gear, perhaps a more
standard alpine gearing would work for you like a
48/36/24. I just think you really beg problems as soon
as your rear cogs get to be the same size as your granny
or smaller.

Quoted message said:

Harris Cyclery carries 110mm bcd chainrings in every size.
Including 41 and 45 teeth. Both T.A. brand, expensive, and
a cheap BMX brand.

Excellent. Thanks.

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

Quoted message said:

2) I'm not seeing the pit falls of the 42/39 yet, other
than the really low gearing. My casual review of the
gear charts (generated from Sheldon's very cool site)
suggest that any 3 tooth jump on the chain rings gets
you really close with most off the shelf cassettes.
More important I would think, is whether or not the
general size of the chain rings is getting the basic
range of gears desired. I think your 48/45 is probably
better in this regard.

I reran the numbers last night using a 42-39, 45-42, and 48-
45 half steps coupled with 14-16-18-21-24-28-32(34) seven
speed off the shelf cassettes and 12-14-16-18-20-23-26-30-34
nine speed off the shelf cassettes. And the 42-39, 45-42,
and 48-45 chainrings work pretty well. I think the 45-42
works best for me. But my current 48-45 and your 42-39 are
just fine too. I now think I will get a 42 chainring and go
with 45-42 half step chainrings. And stay with my current
seven speed 14-16-18-21-24-28-34 cassette. And not spend the
money yet for a nine speed setup.

In answer to a post by another, off the shelf cassettes are
what appeal to me. Buy a seven speed 14-32 or nine speed 12-
34 from Nashbar and put it on the bike and ride.

Quoted message said:

3) I'm still getting my head around your desire for
running a 24t chain ring with 24 - 18 cogs. My gear
charts (again, taken from Sheldon's site) indicate
this is in the gear inch range of 26 to 39 inches or
so. It looks to me that this run of gears is available
with a 36t chain ring on 34 - 28t cogs. If you want
something close to a steady set of step (full, half or
what have you) from a 20 inch gear up to 100 inch
gear, perhaps a more standard alpine gearing would
work for you like a 48/36/24. I just think you really
beg problems as soon as your rear cogs get to be the
same size as your granny or smaller.

I have a 20 tooth inner chainring. 20 tooth. I love really
low gears. A 20 inner chainring gives me a 16 gear inch low
when using my 34 rear cog. If I were to use a normal 24
inner chainring, then I would only have a 19 gear inch low
instead of my current 16 gear inch low. Not as good.

I am going to run chainrings of 45-42-20. I currently run
48-45-20. In the past I used a 24 tooth inner chainring. But
the 20 tooth inner chainring gives me even lower low gears
for no extra effort.

When I run 45-42-20 chainrings with my current 14-16-18-21-24-
34 seven speed cassette cogs, I will have a high gear of 87
gear inches. Not too high but I reckon I can live with it
when touring loaded. I could also purchase a 12-14-16-18-21-24-
28 seven speed off the shelf cassette from Nashbar for $18
to run half step and get a high gear of 101 gear inches and
a low of 19 gear inches when coupled with my soon to be 45-42-
20 chainrings.