Fixed/free combination

Quoted message said:

I've always enjoyed riding fixed, but as I get older I find myself
walking more than I used to. The hills round here (County Fermanagh,
Northern Ireland) are short - generally less than half a mile, but can
be steep.

Some years ago there was a fix/free combination hub that was basically
a clutch. Both fixed and free had the same ratio, which seems a waste.
I'm wondering if it might be possible to modify a hub gear to get
ratios of say 65 fixed and 45 free, so that the free would be usable
uphill as well as down - or would it be better to climb on the fixed an
have the free for the cruising gear?

Several manufacturers offer a double-sided fixed/free rear hub -- Suzue's
hub is probably easiest to find. Put a fixed cog on the fixed side, and a
single speed BMX freewheel on the other side. You can usually get away
with a 2-tooth difference between the two cogs without having to adjust
chain length, provided your dropouts are long enough to take up the
slack.

--

John ([email hidden])

Neat and simple, and it would be a good system on longer hills, but I
wonder if I could chamge over quickly enough for it to be worthwhile.
Would it be possible to mount both on the same side and run with a
double chainwheel?

On Sat, 11 Feb 2006 08:52:43 -0800, [email hidden]

Quoted message said:

Neat and simple, and it would be a good system on longer hills, but I
wonder if I could chamge over quickly enough for it to be worthwhile.
Would it be possible to mount both on the same side and run with a
double chainwheel?

It's impractical to think of a flip-flop wheel as a 2-speed bike. Even
with a quick release (and yes, you can use a quick-release axle), it would
be a PITA to stop and flip the wheel around.

I use mine to have either a bail-out lower gear if I get burned up on a
ride, or to have a slightly bigger gear in case I get in a ride with a
fast group. Mine is fixed-fixed, but that isn't the point.

--

David L. Johnson

__o | When you are up to your ass in alligators, it's hard to remember
_`\(,_ | that your initial objective was to drain the swamp. -- LBJ
(_)/ (_) |

Quoted message said:

Neat and simple, and it would be a good system on longer hills, but I
wonder if I could chamge over quickly enough for it to be worthwhile.
Would it be possible to mount both on the same side and run with a
double chainwheel?

The Rivendell Quickbeam uses two chainrings with a fixed gear to make
it a two (or four) speed bike:
http://www.rivendellbicycles.com/html/bikes_quickbeam.html

Jeff

Quoted message said:

Neat and simple, and it would be a good system on longer hills, but I
wonder if I could chamge over quickly enough for it to be worthwhile.
Would it be possible to mount both on the same side and run with a
double chainwheel?

I'm sure it is possible. Heck I'm sure someone's done that.

But a standard fixed/free hub is dirt cheap and readily
available anywhere. Gear change involves standard cheap
parts that are readily available anywhere. With a simple,
cheap track wrench, one can flip a wheel in a minute (OK two
minutes the first time). So why make it complex?

Standards are standard sometimes because they work well for
most riders in most situations.

--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971

What I have now is a Cannandale Touring frame ca 1990, 27' wheels,
screw-on block. A flip-flop hub won't work on its own because it has
semi-vertical dropouts, so I'd need a double chainring anyway to
compensate for length. I'm thinking of using a single freewheel as a
lockring for a fixed sprocket, because I've had sprockets unscrew on
descents. If the fixed is the higher gear, then that would mean the
smaller sprocket on the inside.

Can this work?

On Mon, 13 Feb 2006 07:32:29 -0800, [email hidden]

Quoted message said:

What I have now is a Cannandale Touring frame ca 1990, 27' wheels,
screw-on block. A flip-flop hub won't work on its own because it has
semi-vertical dropouts, so I'd need a double chainring anyway to
compensate for length.

How does a double chainring compensate for length? Do you mean that, say,
if you have 18 and 20-tooth sprockets, you would have 48 and 46-tooth
chainrings, and use the 48/18 or 46/20? I guess that would work, using
the semi-vertical dropout for some adjustment.

I'm thinking of using a single freewheel as a

Quoted message said:

lockring for a fixed sprocket, because I've had sprockets unscrew on
descents. If the fixed is the higher gear, then that would mean the
smaller sprocket on the inside.

I think the freewheel will interfere with the chain when you try to use
the fixed sprocket. I also wonder whether you would have enough threads
to securely engage the freewheel. I have, in the past, used an old road
hub for a fixed, and there was only just enough thread left to add a
(bottom-bracket) lockring. That would not be enough to hold the
freewheel, and it would just strip those threads off.

--

David L. Johnson

__o | As far as the laws of mathematics refer to reality, they are not
_`\(,_ | certain, and as far as they are certain, they do not refer to
(_)/ (_) | reality. -- Albert Einstein

David L. Johnson said:

On Mon, 13 Feb 2006 07:32:29 -0800, [email hidden]

Quoted message said:

What I have now is a Cannandale Touring frame ca 1990, 27' wheels,
screw-on block.

Those are pretty big wheels! :^)

Quoted message said:

Quoted message said:

I'm thinking of using a single freewheel as a
lockring for a fixed sprocket, because I've had sprockets unscrew on
descents. If the fixed is the higher gear, then that would mean the
smaller sprocket on the inside.

Quoted message said:

I think the freewheel will interfere with the chain when you try to use
the fixed sprocket. I also wonder whether you would have enough threads
to securely engage the freewheel. I have, in the past, used an old road
hub for a fixed, and there was only just enough thread left to add a
(bottom-bracket) lockring. That would not be enough to hold the
freewheel, and it would just strip those threads off.

I'm with David. Maybe you could modify a fixed cog by removing the
shoulder. Now you'd have a few more threads to hold on the freewheel,
but I'm not sure you'd have enough threads left on the fixed cog. I
don't think I've seen a hub with enough threads to support two separate
gears.

Now if you're *really* handy, you could probably machine your own
fixed/free cog assembly. Sorta like the freewheel that's currently on
the bike, but with one fixed and one freewheeling cog. The cogs would
run on the same carrier, and they would both load the same threads. It
would almost certainly be cost prohibitive, though.

--
Dave
dvt at psu dot edu

dvt said:

David L. Johnson said:

On Mon, 13 Feb 2006 07:32:29 -0800, [email hidden]

Quoted message said:

What I have now is a Cannandale Touring frame ca 1990, 27' wheels,
screw-on block.

Those are pretty big wheels! :^)

Quoted message said:

Quoted message said:

I'm thinking of using a single freewheel as a
lockring for a fixed sprocket, because I've had sprockets unscrew on
descents. If the fixed is the higher gear, then that would mean the
smaller sprocket on the inside.

Quoted message said:

I think the freewheel will interfere with the chain when you try to use
the fixed sprocket. I also wonder whether you would have enough threads
to securely engage the freewheel. I have, in the past, used an old road
hub for a fixed, and there was only just enough thread left to add a
(bottom-bracket) lockring. That would not be enough to hold the
freewheel, and it would just strip those threads off.

I'm with David. Maybe you could modify a fixed cog by removing the
shoulder. Now you'd have a few more threads to hold on the freewheel,
but I'm not sure you'd have enough threads left on the fixed cog. I
don't think I've seen a hub with enough threads to support two separate
gears.

This might be old news. If so, sorry.
<http://www.basementfreaks.com/gallery/gallery.php?gal=7205f55d4003b20e1e0e07035a45dafd>
or if that gets mangled:
http://tinyurl.com/cmnka
\\paul

Paul Hobson said:

This might be old news. If so, sorry.
<http://www.basementfreaks.com/gallery/gallery.php?gal=7205f55d4003b20e1e0e07035a45dafd>
or if that gets mangled:
http://tinyurl.com/cmnka

Well, it is old news, in that the design is from the early 20th century.
For those who did not follow the link, this is one of those two-speed
arrangements where the low gear is engaged when you pedal backwards. It
also is not a fixed/free combination, and most of us would find it pretty
awkward to use.

--

David L. Johnson

__o | And though I have the gift of prophecy, and understand all
_`\(,_ | mysteries, and all knowledge; and though I have all faith, so
(_)/ (_) | that I could remove mountains, and have not charity, I am
nothing. [1 Corinth. 13:2]

David L. Johnson said:

Paul Hobson said:

This might be old news. If so, sorry.
<http://www.basementfreaks.com/gallery/gallery.php?gal=7205f55d4003b20e1e0e07035a45dafd>
or if that gets mangled:
http://tinyurl.com/cmnka

Well, it is old news, in that the design is from the early 20th century.
For those who did not follow the link, this is one of those two-speed
arrangements where the low gear is engaged when you pedal backwards. It
also is not a fixed/free combination, and most of us would find it pretty
awkward to use.

It did have the clever feature of using an old BB cup to
extend the hub threading so that both freewheels could
be mounted. This might be applied to the fixed/free idea,
although you would have to be careful to get everything
spaced right so that all the parts had some thread engagement.

Quoted message said:

email hidden said:

Some years ago there was a fix/free combination hub that was basically
a clutch. Both fixed and free had the same ratio, which seems a waste.
I'm wondering if it might be possible to modify a hub gear to get
ratios of say 65 fixed and 45 free, so that the free would be usable
uphill as well as down - or would it be better to climb on the fixed an
have the free for the cruising gear?

Sorting through a traditional bike shop's bin of old hub gears a few
years ago looking for four speed hubs I came across what I think was an
internal gear hub with a second inner sprocket mounted on the hub shell.
It was the only one the shop owner would not part with so I got no
closer than that. Maybe it was a freewheel coaster brake on the outer
sprocket and fixed on the inner. I think it was German or Swedish made
may be Thun or Thor. The main shell was fairly slim. This would require
stopping and manual (digital) changing so it might not be that much
better than the double sided hub.

The Sturmey Archer AW three and FW four speeds can be modified to multi
speed fixed.

Graham Webster has done both a SA and Sachs 3 speeds to 2 speed fixed.
This page has a link about half way down the TechArticles to a pdf:

http://www.fixedgeargallery.com/

To get what you want based on a Sachs Torpedo 3 the right hand ratchet
would need to be replaced to provide a fixed drive (as Graham has done)
but it would have to be disengaged for a freewheeling low gear delivered
through the other ratchet. I do not know if this is feasible. My memory
of the Sachs design is that the right hand ratchet disengages for low
gear by moving off the ratchet track (unlike the 1920s onwards SA gears
where the ratchet pawls are tripped from the inside). In which case I'm
not sure why Graham's modified gear provides drive in gear 1. I've not
got a Sachs to hand to check at the moment. This modification (should it
be possible) would give you two speed fixed and a third low free gear.

The Torpedo threes that turn up on dumped Dutch bikes here are normally
coaster brake but you should be able to get a new freewheel type from
your local Brompton dealer or more sensibly a damaged one to
investigate.

--

Martyn Aldis, e-mail [email hidden]
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