Best front derailleur for half step plus granny

[pinnah]

[email protected] (Russell Seaton) wrote:
>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.


>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
==============================================

 

[Russell Seaton]

> 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.

> 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.