expanding gear ratio on 3-speed revisited

I'm resurrecting an old project of mine, which requires expanding the
gear ratio of a 3 speed. Thanks to helpful posters I now have an idea on
how to tackle the problem( adding a front tripple, or maybe even a front
quad conversion), which tooth counts to use, and where to get the
chainwheels.

But during my research I've come across two recommendations that I'd
like your comments on:
1) TA says that you should have at least an 8 tooth difference between
chain wheels, why?
Is it to get a good span assuming an ordinary rear cassette,(which
wouldn't apply to me) or has it something to do with gear change
performance?(which is something that I'd like to consider)

2) Somewhere on the site ctc.org.uk there is a recommendation that 15%
or even 25% steps in ratios are fine.
If I can achieve increments of about 7.5%, would that be worthwhile or
overshooting the mark? (I dunno, some people seem to find corncob
cassettes useful...)

Cheers,

dabac


--
dabac

someone writes:

I'm resurrecting an old project of mine, which requires expanding
the gear ratio of a 3 speed. Thanks to helpful posters I now have an
idea on how to tackle the problem (adding a front triple, or maybe
even a front quad conversion), which tooth counts to use, and where
to get the chainwheels.

But during my research I've come across two recommendations that I'd
like your comments on:

1) TA says that you should have at least an 8 tooth difference
between chain wheels, why?

Is it to get a good span assuming an ordinary rear cassette,(which
wouldn't apply to me) or has it something to do with gear change
performance? (which is something that I'd like to consider)

2) Somewhere on the site ctc.org.uk there is a recommendation that
15% or even 25% steps in ratios are fine.

If I can achieve increments of about 7.5%, would that be worthwhile
or overshooting the mark? (I dunno, some people seem to find corncob
cassettes useful...)

Why use a hub gear at all if you are already putting a rear derailleur
on to take up chain length between three or four sprockets in the
front? The internal gear brings no advantages. If you insist on
using the 3-speed hub you are best served by a three or four speed
cluster on the outside of the hub, as was often done forty years ago.

Jobst Brandt

Wrote:

Why use a hub gear at all if you are already putting a rear derailleur
on to take up chain length between three or four sprockets in the
front? Because I've got a set of composite wheels that I'd like to use, and
the rear wheel comes with a S-A hub heavily integrated.
I'm hesitant as to whether I'd be able to remove it to make room for
something else w/o destroying the wheel.

Wrote:
The internal gear brings no advantages But it's what comes with the wheel. It's still the "easiest" route by
far to base the updated drivtrain around what's already there if I want
to use these wheels.

Wrote:
If you insist on
using the 3-speed hub you are best served by a three or four speed
cluster on the outside of the hub,

And where would I find such a thing in serviceable condition? My
workaround is at least doable with components that are still in
production.


--
dabac

Wrote:
Why use a hub gear at all if you are already putting a rear derailleur
on to take up chain length between three or four sprockets in the
front? Because I've got a set of composite wheels that I'd like to use, and
the rear wheel comes with a S-A hub heavily integrated.
I'm hesitant as to whether I'd be able to remove it to make room for
something else w/o destroying the wheel.

Wrote:
The internal gear brings no advantages But it's what comes with the wheel. It's still the "easiest" route by
far to base the updated drivtrain around what's already there if I want
to use these wheels.

Wrote:
If you insist on
using the 3-speed hub you are best served by a three or four speed
cluster on the outside of the hub,

dabac wrote:
And where would I find such a thing in serviceable condition? My
workaround is at least doable with components that are still in
production.

The usual sub for the Cyclo adapter is a Sturmey threaded driver with a
blocked freewheel screwed on it. A single front with 2 or 3 rear cogs
can nicely split the big gearing steps (-25%, direct, +33%) of an AW
into useful gears.
--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971

aka Jobst Brandt wrote:

Why use a hub gear at all if you are already putting a rear derailleur
on to take up chain length between three or four sprockets in the
front? The internal gear brings no advantages. If you insist on
using the 3-speed hub you are best served by a three or four speed
cluster on the outside of the hub, as was often done forty years ago.

Today you can buy the same thing brand new, except with an 8 or 9-speed
cassette attached to the 3-speed hub - see SRAM DualDrive.

The DualDrive was of course preceded by the SRAM/Sachs 3x7 hub, which
used the "Torpedo Dreigang" internals and was in production up to 2001.
There was also a Sachs 2x6 version at an earlier time.

The internal geared hub is particularly advantageous on small drive
wheel bicycles, since front derailers that handle anything more than
63/52/39 teeth are not to be found, unless custom made.

--
Tom Sherman - Holstein-Friesland Bovinia
The weather is here, wish you were beautiful

Tom Sherman Wrote:
Today you can buy the same thing brand new, except with an 8 or 9-speed
cassette attached to the 3-speed hub - see SRAM DualDrive.

But is there anything like that available today that would fit the
sprocket thread of an old S-A hub?


--
dabac

Tom Sherman Wrote:
There was also a Sachs 2x6 version at an earlier time.

I've got one of those in the parts bin. Haven't been able to figure out
how the cassette is attached though...


--
dabac

on my folder I just put an extra chainwheel with no front derailluer,
shift by hand or foot

Tom Sherman Wrote:
Today you can buy the same thing brand new, except with an 8 or 9-speed
cassette attached to the 3-speed hub - see SRAM DualDrive.

dabac wrote:
But is there anything like that available today that would fit the
sprocket thread of an old S-A hub?

any freewheel, just block the body.
--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971

A Muzi Wrote:
Tom Sherman Wrote:
Today you can buy the same thing brand new, except with an 8 or
9-speed
cassette attached to the 3-speed hub - see SRAM DualDrive.

dabac wrote:
But is there anything like that available today that would fit the
sprocket thread of an old S-A hub?

any freewheel, just block the body.

Wow, really? Like a low-end Shimano 7-spd freehub?
I really gotta get my eyesight calibrated in that case, 'cause the
diameter of the hub sure looked way too large for that to me.


--
dabac