Fixed Gear -- Magic Ratios?

In article <[email hidden]>,

jack sprat said:

Hi,

I'm wondering if there is anyway to find out what "magic"
combinations of chainwheel/sprockets that would yield exactly the
same chainlength, but different gear ratios.

I want the easiest, no-fuss gear-inch change possible (when flipping
over the back wheel) and the means no fiddling with chain length
(which would mean fiddling with tire/fender clearance as well as
brake/rim alignment [unless I had the "magic" angle on my
rear-dropouts, which I don't. b.t.w. what exactly is this magic
angle and how can I get a bike with it?]), but moving the chain to
another chainring up front is no problem.

Yup. Check Eric House's and Sheldon Brown's Web sites for software to
do these calculations for you.

Well. I may be wrong, but an Occam 's Razor would say any combination
that when added together resulted in the same amount of total teeth. IE:
48-12 and 44-16.

- -
Comments and opinions compliments of,
"Your Friendly Neighborhood Wheelman"

My web Site:
http://geocities.com/czcorner

To E-mail me:
ChrisZCorner "at" webtv "dot" net

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In article <[email hidden]>,

jack sprat said:

Hi,

I'm wondering if there is anyway to find out what "magic" combinations of
chainwheel/sprockets that would yield exactly the same chainlength, but
different gear ratios.

I want the easiest, no-fuss gear-inch change possible (when flipping over
the back wheel) and the means no fiddling with chain length (which would
mean fiddling with tire/fender clearance as well as brake/rim alignment
[unless I had the "magic" angle on my rear-dropouts, which I don't. b.t.w.
what exactly is this magic angle and how can I get a bike with

it?]),

The tangent to the circle with radius of the wheel centered at
the brake shoe comes close. Or at least that's best mental
geometry I can do on only two cups of coffee...

Quoted message said:

but
moving the chain to another chainring up front is no problem.

Any ideas?

_ You want FixMeUP it one of it's various forms.

http://eehouse.org/fixin/

_ Booker C. Bense

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In article <[email hidden]>,

jack sprat said:

Hi,

I'm wondering if there is anyway to find out what "magic"
combinations of chainwheel/sprockets that would yield exactly the
same chainlength, but different gear ratios.

I want the easiest, no-fuss gear-inch change possible (when flipping
over the back wheel) and the means no fiddling with chain length
(which would mean fiddling with tire/fender clearance as well as
brake/rim alignment [unless I had the "magic" angle on my
rear-dropouts, which I don't. b.t.w. what exactly is this magic
angle and how can I get a bike with it?])

Buy a Rivendell Quickbeam.

Tim McNamara said:

In article <[email hidden]>,

jack sprat said:

Hi,

I'm wondering if there is anyway to find out what "magic" combinations
of chainwheel/sprockets that would yield exactly the same chainlength,
but different gear ratios.

I want the easiest, no-fuss gear-inch change possible (when flipping
over the back wheel) and the means no fiddling with chain length (which
would mean fiddling with tire/fender clearance as well as brake/rim
alignment [unless I had the "magic" angle on my rear-dropouts, which I
don't. b.t.w. what exactly is this magic angle and how can I get a
bike with it?]), but moving the chain to another chainring up front is
no problem.

Yup. Check Eric House's and Sheldon Brown's Web sites for software to
do these calculations for you.

I don't know about a "magic angle" but even with vertical dropouts there
are good fixed gear solutions available these days -- hubs with eccentric
axle ends, chain half-links, etc.

As far as gearing goes, obviously, you can just add teeth to a cog and
subtract the same number from a chainring, and vice versa. Use Sheldon
Brown's gear calculator to compare the gear combinations. The best way to
find the right gears for you is to find the one or two gears on your
mult-speed bike that work best for everything.

I noticed several dual-speed fixies in London last time, with two
chainrings and flip-flop hubs with corresponding cogs. London is
perfectly suited for fixed gear riding because it's as flat
as a billiard table. It's easier to pace the slow stop and go traffic on
a fixed gear, rather than pedal-coast-brake all the time. And it rains so
much that anything that cuts bike maintenance is a plus.

Matt O.

jack sprat said:

Hi,

I'm wondering if there is anyway to find out what "magic" combinations of
chainwheel/sprockets that would yield exactly the same chainlength, but
different gear ratios.

I want the easiest, no-fuss gear-inch change possible (when flipping over
the back wheel) and the means no fiddling with chain length (which would
mean fiddling with tire/fender clearance as well as brake/rim alignment
[unless I had the "magic" angle on my rear-dropouts, which I don't. b.t.w.
what exactly is this magic angle and how can I get a bike with it?]), but
moving the chain to another chainring up front is no problem.
Any ideas?
Thanks,
J.

I think you've missed something. When you flip the wheel to change gear
you will have to retension the chain anyway, regardless for what CW/cog
combo that you use. There is a trick to retensioning easily but it's a
bit difficult to describe. Basically you [censored] the wheel to the non
drive side, tighten the lock nut on that side, leaving the drive side
loose, Then you push the rim over to the right, tensioning the chain
and then tighten the drive side. Then loosen the non drive side, center
the wheel and Bob's your uncle. It's a lot easier to do than describe.
Phil Brown

philcycles said:

jack sprat said:

Hi,

I'm wondering if there is anyway to find out what "magic" combinations of
chainwheel/sprockets that would yield exactly the same chainlength, but
different gear ratios.

I want the easiest, no-fuss gear-inch change possible (when flipping over
the back wheel) and the means no fiddling with chain length (which would
mean fiddling with tire/fender clearance as well as brake/rim alignment
[unless I had the "magic" angle on my rear-dropouts, which I don't. b.t.w.
what exactly is this magic angle and how can I get a bike with it?]), but
moving the chain to another chainring up front is no problem.
Any ideas?
Thanks,
J.

I think you've missed something. When you flip the wheel to change gear
you will have to retension the chain anyway, regardless for what CW/cog
combo that you use. There is a trick to retensioning easily but it's a
bit difficult to describe. Basically you [censored] the wheel to the non
drive side, tighten the lock nut on that side, leaving the drive side
loose, Then you push the rim over to the right, tensioning the chain
and then tighten the drive side. Then loosen the non drive side, center
the wheel and Bob's your uncle. It's a lot easier to do than describe.
Phil Brown

I just tug the wheel back with one hand & flip the Q/R with the other --
easy-peasy.

Peter Cole said:

I just tug the wheel back with one hand & flip the Q/R with the other --
easy-peasy.

Most of the time a fixed rear wheel has lock nuts, not a quick release.
Phil Brown