making sense of gears

[catzz66]

Is there a good discussion of gears that anyone would recommend? I
looked at a Specialized Langster in a bike shop (I'm not really in the
market, just curious) and wondered how I could get close to the 48/16
gearing it comes with on one of my bikes. I realize that I really don't
know much about gears.

 

[David L. Johnson]

On Thu, 06 Apr 2006 16:31:37 -0500, catzz66 wrote:

> Is there a good discussion of gears that anyone would recommend? I
> looked at a Specialized Langster in a bike shop (I'm not really in the
> market, just curious) and wondered how I could get close to the 48/16
> gearing it comes with on one of my bikes. I realize that I really don't
> know much about gears.

I suppose that getting a 48-tooth chainring and a 16-tooth cog is not what
you are asking about. In fact, I suppose you have a road bike, and want
to see what gear on your road bike is closest to this. A 52/17 is just a
bit higher a gear than the 48/16. IMO (NSH), a 48/16 is a bit big for
tooling around. I use a 48/19 in the winter and a 48/18 in the Summer.
It does depend upon your preferences, and the terrain, however. If you
have a lot of hills, or like to spin, then go lower.

But this should have 0 impact on your decision whether or not to buy such
a bike. Sprockets are cheap, and anyone riding fixed gear bikes should
have several.

--

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
(_)/ (_) |

 

[catzz66]

David L. Johnson wrote:
>
>
> I suppose that getting a 48-tooth chainring and a 16-tooth cog is not what
> you are asking about. In fact, I suppose you have a road bike, and want
> to see what gear on your road bike is closest to this. A 52/17 is just a
> bit higher a gear than the 48/16. IMO (NSH), a 48/16 is a bit big for
> tooling around. I use a 48/19 in the winter and a 48/18 in the Summer.
> It does depend upon your preferences, and the terrain, however. If you
> have a lot of hills, or like to spin, then go lower.
>
> But this should have 0 impact on your decision whether or not to buy such
> a bike. Sprockets are cheap, and anyone riding fixed gear bikes should
> have several.
>

I believe I have about a 52/39 chainring and my smallest cog in the rear
is 12 teeth. I guess what I am asking is how I could mathematically
come close to matching the 48/16 to see how it ought to feel. I am
trying to think through the logic of it.

 

[Leo Lichtman]

"catzz66" wrote: (clip) I guess what I am asking is how I could
mathematically come close to matching the 48/16 to see how it ought to
feel. I am trying to think through the logic of it.
^^^^^^^^^^^^^^
48/16=3. Whatever number of teeth you have on the chainring will determine
what is needed on the cog--simply divide by 3. If you use the 52 tooth
ring, 52/3= 17.3, so you will be pretty close with a 17 tooth cog.
Similarly, your 39 tooth ring will call for a 13 tooth cog.

 

[catzz66]

Leo Lichtman wrote:
> "catzz66" wrote: (clip) I guess what I am asking is how I could
> mathematically come close to matching the 48/16 to see how it ought to
> feel. I am trying to think through the logic of it.
> ^^^^^^^^^^^^^^
> 48/16=3. Whatever number of teeth you have on the chainring will determine
> what is needed on the cog--simply divide by 3. If you use the 52 tooth
> ring, 52/3= 17.3, so you will be pretty close with a 17 tooth cog.
> Similarly, your 39 tooth ring will call for a 13 tooth cog.
>
>


Thanks. That's simple enough. So, my 39 tooth ring and 12 tooth gear
ought to be a little harder than 48/16 would be.

 

[(PeteCresswell)]

Per catzz66:
>Is there a good discussion of gears that anyone would recommend? I
>looked at a Specialized Langster in a bike shop (I'm not really in the
>market, just curious) and wondered how I could get close to the 48/16
>gearing it comes with on one of my bikes. I realize that I really don't
>know much about gears.

Not a discussion, but Sheldon's gear calculator would let you get a feel for
what's closer to what...

http://www.sheldonbrown.com/gears/
--
PeteCresswell

 

[Werehatrack]

On Thu, 06 Apr 2006 18:29:10 -0500, catzz66 <[email protected]>
wrote:

>Leo Lichtman wrote:
>> "catzz66" wrote: (clip) I guess what I am asking is how I could
>> mathematically come close to matching the 48/16 to see how it ought to
>> feel. I am trying to think through the logic of it.
>> ^^^^^^^^^^^^^^
>> 48/16=3. Whatever number of teeth you have on the chainring will determine
>> what is needed on the cog--simply divide by 3. If you use the 52 tooth
>> ring, 52/3= 17.3, so you will be pretty close with a 17 tooth cog.
>> Similarly, your 39 tooth ring will call for a 13 tooth cog.
>>
>>
>
>
>Thanks. That's simple enough. So, my 39 tooth ring and 12 tooth gear
>ought to be a little harder than 48/16 would be.

Yes, but by the same token, 52/17 will also be a trifle taller than
the 48/16 combo. If you have a 52 sprocket in front, it's essentially
certain that you've already got at least one rear that's 17 teeth or
less, so "taller than 48/16" is pretty much assured for some
combination that you have now. I'm borrowing the automotive use of
"taller" here, in which it implies a gear ratio that requires fewer
powerplant revs for a given number of wheel revs than for a ratio
that's not as tall. In a more bike-centric form of expression, the
discussion would be centered around gear-inches, which also takes into
account the wheel diameter...which is relevant, after all.
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.

 

[Phil, Squid-in-Training]

catzz66 wrote:
> Is there a good discussion of gears that anyone would recommend? I
> looked at a Specialized Langster in a bike shop (I'm not really in the
> market, just curious) and wondered how I could get close to the 48/16
> gearing it comes with on one of my bikes. I realize that I really
> don't know much about gears.

Keep in mind that large cogs wear more slowly than small ones, and they also
have less ground clearance for going down stairs and such.
--
Phil, Squid-in-Training

 

[Michael Press]

In article <[email protected]>,
catzz66 <[email protected]> wrote:

> Leo Lichtman wrote:
> > "catzz66" wrote: (clip) I guess what I am asking is how I could
> > mathematically come close to matching the 48/16 to see how it ought to
> > feel. I am trying to think through the logic of it.
> > ^^^^^^^^^^^^^^
> > 48/16=3. Whatever number of teeth you have on the chainring will determine
> > what is needed on the cog--simply divide by 3. If you use the 52 tooth
> > ring, 52/3= 17.3, so you will be pretty close with a 17 tooth cog.
> > Similarly, your 39 tooth ring will call for a 13 tooth cog.
> >
> >
>
>
> Thanks. That's simple enough. So, my 39 tooth ring and 12 tooth gear
> ought to be a little harder than 48/16 would be.

Easiest way to do this is with a slide rule; but you need
to have one and know how to use it.

Mathematics made difficult:
How to compare 42 / 16 <=> 53 / 20 ?

These fractions have the same relationship as

42 * 20 <=> 53 * 16 or 820 <=> 848. Therefore
42 / 16 < 53 / 20.

39 / 12 <=> 48 / 16
--> 39 * 16 <=> 12 * 48
--> 39 <=> 12 * 3
--> 39 <=> 36.

--
Michael Press

 

[Greg]

Michael Press wrote:
> In article <[email protected]>,
> catzz66 <[email protected]> wrote:
>
> > Leo Lichtman wrote:
> > > "catzz66" wrote: (clip) I guess what I am asking is how I could
> > > mathematically come close to matching the 48/16 to see how it ought to
> > > feel. I am trying to think through the logic of it.
> > > ^^^^^^^^^^^^^^
> > > 48/16=3. Whatever number of teeth you have on the chainring will determine
> > > what is needed on the cog--simply divide by 3. If you use the 52 tooth
> > > ring, 52/3= 17.3, so you will be pretty close with a 17 tooth cog.
> > > Similarly, your 39 tooth ring will call for a 13 tooth cog.
> > >
> > >
> >
> >
> > Thanks. That's simple enough. So, my 39 tooth ring and 12 tooth gear
> > ought to be a little harder than 48/16 would be.
>
> Easiest way to do this is with a slide rule; but you need
> to have one and know how to use it.
>
> Mathematics made difficult:
> How to compare 42 / 16 <=> 53 / 20 ?
>
> These fractions have the same relationship as
>
> 42 * 20 <=> 53 * 16 or 820 <=> 848. Therefore
> 42 / 16 < 53 / 20.
>
> 39 / 12 <=> 48 / 16
> --> 39 * 16 <=> 12 * 48
> --> 39 <=> 12 * 3
> --> 39 <=> 36.
>
> --
> Michael Press

Or, if you have a computer and a spreadsheet program like excel, just
build a table. It takes 5 minutes and then you have a reference of
every gear inch.

Sliderules...really now.

Greg

 

[catzz66]

Werehatrack wrote:
>
>
> Yes, but by the same token, 52/17 will also be a trifle taller than
> the 48/16 combo. If you have a 52 sprocket in front, it's essentially
> certain that you've already got at least one rear that's 17 teeth or
> less, so "taller than 48/16" is pretty much assured for some
> combination that you have now. I'm borrowing the automotive use of
> "taller" here, in which it implies a gear ratio that requires fewer
> powerplant revs for a given number of wheel revs than for a ratio
> that's not as tall. In a more bike-centric form of expression, the
> discussion would be centered around gear-inches, which also takes into
> account the wheel diameter...which is relevant, after all.

I rechecked the cassette when I got home. My chainring is a 53/39 and I
have a 12/13.../23 8 speed cassette, so the 39/13 is the same ratio as
the Langster's 48/16. I already know that is a good ratio for me from
my old bike. Thanks, everyone.

 

[Leo Lichtman]

"Greg" wrote: Or, if you have a computer and a spreadsheet program like
excel, just build a table. It takes 5 minutes and then you have a reference
of every gear inch. Sliderules...really now.
^^^^^^^^^^^^^^^^^^^
A computer? Really now. Look around for a stub of a pencil and a scrap of
paper. That will work on the trail, in the driveway or on the kitchen
table.

 

[David L. Johnson]

On Thu, 06 Apr 2006 17:31:29 -0500, catzz66 wrote:

> David L. Johnson wrote:

>>
>
> I believe I have about a 52/39 chainring and my smallest cog in the rear
> is 12 teeth. I guess what I am asking is how I could mathematically
> come close to matching the 48/16 to see how it ought to feel. I am
> trying to think through the logic of it.

Like I said, the 52/17 is close. As far as the logic goes, It is the
ratio that matters. 48/16=3 52/17 = 3.06. Us old farts usually express
gear ratios in terms of "gear inches", multiplying that ratio by the
diameter of the wheel. The 48/16 is then about an 81" gear (using 27"),
but really is more like an 80" or a bit less since most wheels are shy of
27".

--

David L. Johnson

__o | Deserves death! I daresay he does. Many that live deserve
_`\(,_ | death. And some that die deserve life. Can you give it to
(_)/ (_) | them? Then do not be too eager to deal out death in judgement.
-- J. R. R. Tolkein

 

[David L. Johnson]

On Fri, 07 Apr 2006 05:01:20 +0000, Michael Press wrote:

>>
>> Thanks. That's simple enough. So, my 39 tooth ring and 12 tooth gear
>> ought to be a little harder than 48/16 would be.
>
> Easiest way to do this is with a slide rule; but you need
> to have one and know how to use it.

A slide rule!!! Oh, wait, I do have one...

--

David L. Johnson

__o | It is a scientifically proven fact that a mid life crisis can
_`\(,_ | only be cured by something racy and Italian. Bianchis and
(_)/ (_) | Colnagos are a lot cheaper than Maserattis and Ferraris. --
Glenn Davies

 

[David L. Johnson]

On Fri, 07 Apr 2006 06:04:56 -0700, Greg wrote:

> Or, if you have a computer and a spreadsheet program like excel, just
> build a table. It takes 5 minutes and then you have a reference of
> every gear inch.

"If" you have a computer? What do you think you're looking at right now?

--

David L. Johnson

__o | Do not worry about your difficulties in mathematics, I can
_`\(,_ | assure you that mine are all greater. -- A. Einstein
(_)/ (_) |

 

[Michael Press]

In article
<[email protected]>,
"Greg" <[email protected]> wrote:

> Michael Press wrote:
> > In article <[email protected]>,
> > catzz66 <[email protected]> wrote:
> >
> > > Leo Lichtman wrote:
> > > > "catzz66" wrote: (clip) I guess what I am asking is how I could
> > > > mathematically come close to matching the 48/16 to see how it ought to
> > > > feel. I am trying to think through the logic of it.
> > > > ^^^^^^^^^^^^^^
> > > > 48/16=3. Whatever number of teeth you have on the chainring will determine
> > > > what is needed on the cog--simply divide by 3. If you use the 52 tooth
> > > > ring, 52/3= 17.3, so you will be pretty close with a 17 tooth cog.
> > > > Similarly, your 39 tooth ring will call for a 13 tooth cog.
> > > >
> > > >
> > >
> > >
> > > Thanks. That's simple enough. So, my 39 tooth ring and 12 tooth gear
> > > ought to be a little harder than 48/16 would be.
> >
> > Easiest way to do this is with a slide rule; but you need
> > to have one and know how to use it.
> >
> > Mathematics made difficult:
> > How to compare 42 / 16 <=> 53 / 20 ?
> >
> > These fractions have the same relationship as
> >
> > 42 * 20 <=> 53 * 16 or 820 <=> 848. Therefore
> > 42 / 16 < 53 / 20.
> >
> > 39 / 12 <=> 48 / 16
> > --> 39 * 16 <=> 12 * 48
> > --> 39 <=> 12 * 3
> > --> 39 <=> 36.
> >
> > --
> > Michael Press
>
> Or, if you have a computer and a spreadsheet program like excel, just
> build a table. It takes 5 minutes and then you have a reference of
> every gear inch.
>
> Sliderules...really now.

I built such a table and it is right at hand. For
comparing ratios, nothing beats a slide rule. Set it at
42/16 and read _all_ the equivalent ratios. The method is
easier than the table for two reasons:

* In a table you need to follow a curve in the
2-dimensional table to track the ratio, then read along
the table axes to find the cog counts one at a time.

With a slide rule I am always reading a straight line and
all the cog counts are right there.

* In a table when (as always!) the ratio for 39/17 is
present only for 39/17, you must interpolate to find the
approximate rear cogwheel that corresponds to a 42 cog
chain wheel.

With a slide rule I immediately read 39/17 is equivalent
to 42/18.4 and 34/14.8.

Just for fun I looked at ebay and saw many slide rules
with bids at $20 and less. The exact model that I bought
new started at $10, and is selling for the same number of
dollars I paid at the time.

--
Michael Press

 

[Greg]

Leo Lichtman wrote:
> "Greg" wrote: Or, if you have a computer and a spreadsheet program like
> excel, just build a table. It takes 5 minutes and then you have a reference
> of every gear inch. Sliderules...really now.
> ^^^^^^^^^^^^^^^^^^^
> A computer? Really now. Look around for a stub of a pencil and a scrap of
> paper. That will work on the trail, in the driveway or on the kitchen
> table.

Well, if you have a printer, you could print it out and carry it in
your pocket, tape it to your stem, or whatever.

Of course, you could take the pencil, transpose the numbers in the
table to paper and do the same.

I can't imagine fitting a sliderule in my seatbag.

Details, details, it's always in the details...