formula for gear rations, speeds

"Raymo853" <[email hidden]> wrote in message
"]news:[email hidden]...

Quoted message said:

I got the formula to calculate gear inches (crank teeth count /cog

teeth

Quoted message said:

count) * wheel diameter in inches. But what would it be for say

MPH at 100

Quoted message said:

rmp? For some reason I" am having a bad brain moment and can't get

the

Quoted message said:

conversions correctly.

(Crank Teeth) / (Cog Teeth) * (Wheel diameter in inches) / (12 in per ft) * pi * RPM * (60 min per
hr) / (5280 ft per mi)

Raymo853 said:

I got the formula to calculate gear inches (crank teeth count /cog teeth count) * wheel diameter
in inches. But what would it be for say MPH at 100 rmp? For some reason I" am having a bad brain
moment and can't get the conversions correctly.

MPH @ 100 RPM is one of the modes offered in my online gear calculator:

sheldonbrown.comgearsOpen ↗

But the default units are Gain Ratios, which I think are a better system.

sheldonbrown.comgainOpen ↗

Sheldon "Gain Ratio" Brown +--------------------------------------+
| Without deviation from the norm, | progress is not possible | -- Frank Zappa |
+--------------------------------------+ Harris Cyclery, West Newton, Massachusetts Phone 617-244-
9772 FAX 617-244-1041 harriscyclery.comharriscyclery.comOpen ↗ Hard-to-find parts shipped Worldwide
captainbike.comcaptainbike.comOpen ↗ sheldonbrown.comsheldonbrown.comOpen ↗

Gear ratios calculations are better for some situtations, however, I am concerned about MPH at a
certain RMP while considering cassette choices for an upcoming race.

"Sheldon Brown" <[email hidden]> wrote in message
"]news:[email hidden]...

Quoted message said:

Raymo853 said:

I got the formula to calculate gear inches (crank teeth count /cog teeth count) * wheel diameter
in inches. But what would it be for say MPH at

100

Quoted message said:

Quoted message said:

rmp? For some reason I" am having a bad brain moment and can't get the conversions correctly.

MPH @ 100 RPM is one of the modes offered in my online gear calculator:

sheldonbrown.comgearsOpen ↗

But the default units are Gain Ratios, which I think are a better system.

sheldonbrown.comgainOpen ↗

Sheldon "Gain Ratio" Brown +--------------------------------------+
| Without deviation from the norm, | progress is not possible | -- Frank Zappa |
+--------------------------------------+ Harris Cyclery, West Newton, Massachusetts Phone 617-244-
9772 FAX 617-244-1041 harriscyclery.comharriscyclery.comOpen ↗ Hard-to-find parts shipped Worldwide
captainbike.comcaptainbike.comOpen ↗ sheldonbrown.comsheldonbrown.comOpen ↗

Quoted message said:

Gear ratios calculations are better for some situtations, however, I am concerned about MPH at a
certain RMP while considering cassette choices

for

Quoted message said:

an upcoming race.

You can try EasyGear (ultimade.nlindex.php4Open ↗) if you're willing
to use metric values.

"Raymo853" <[email hidden]> wrote in message "]news:[email hidden]...

Quoted message said:

Gear ratios calculations are better for some situtations, however, I am concerned about MPH at a
certain RMP while considering cassette choices

for

Quoted message said:

an upcoming race.

"Sheldon Brown" <[email hidden]> wrote in message
"]news:[email hidden]...

Quoted message said:

Raymo853 said:

I got the formula to calculate gear inches (crank teeth count /cog

teeth

Quoted message said:

Quoted message said:

Quoted message said:

count) * wheel diameter in inches. But what would it be for say MPH

at

Quoted message said:

100

Quoted message said:

Quoted message said:

rmp? For some reason I" am having a bad brain moment and can't get

the

Quoted message said:

Quoted message said:

Quoted message said:

conversions correctly.

MPH @ 100 RPM is one of the modes offered in my online gear calculator:

sheldonbrown.comgearsOpen ↗

But the default units are Gain Ratios, which I think are a better

system.

Quoted message said:

Quoted message said:

sheldonbrown.comgainOpen ↗

Sheldon "Gain Ratio" Brown +--------------------------------------+
| Without deviation from the norm, | progress is not possible | -- Frank Zappa |
+--------------------------------------+ Harris Cyclery, West Newton, Massachusetts Phone 617-244-
9772 FAX 617-244-1041 harriscyclery.comharriscyclery.comOpen ↗ Hard-to-find parts shipped Worldwide
captainbike.comcaptainbike.comOpen ↗ sheldonbrown.comsheldonbrown.comOpen ↗

On Tue, 2 Mar 2004 07:38:32 -0500, "Raymo853" <[email hidden]> wrote:

<Gear ratios calculations are better for some situtations, however, I am <concerned about MPH at a
certain RMP while considering cassette choices for <an upcoming race.

Why not check out the course and let your experience be your guide?

"Raymo853" <[email hidden]> wrote in message news:<[email hidden]>...

Quoted message said:

I got the formula to calculate gear inches (crank teeth count /cog teeth count) * wheel diameter
in inches. But what would it be for say MPH at 100 rmp? For some reason I" am having a bad brain
moment and can't get the conversions correctly.

Dear Raymond,

Here's an ancient spreadsheet that should import into almost any modern spreadsheet:

home.comcast.netGear3.wk1Open ↗

It lets you set the number of front teeth and the rear wheel diameter and shows RPM versus MPH for a
wide range of rear cogs.

Here's where you can see roughly the same question, with a few pages of output that might be all
that you want:

groups.google.comgroupsOpen ↗

Good luck,

Carl Fogel

Carl fogeled:

<< Dear Raymond,

Here's an ancient spreadsheet that should import into almost any modern spreadsheet:

home.comcast.netGear3.wk1Open ↗

It lets you set the number of front teeth and the rear wheel diameter and shows RPM versus MPH for a
wide range of rear cogs.

Here's where you can see roughly the same question, with a few pages of output that might be all
that you want:

groups.google.comgroupsOpen ↗
g.google.com&output=gplain

Good luck,

Carl Fogel >>

Carl, I'm surprised at you. No mention of crank length? I thought we were all getting behind Sheldon
in the Real Gearing Revolution.

Robert

"Carl Fogel" <[email hidden]> wrote in message >

Quoted message said:

It lets you set the number of front teeth

I'd give anything for my two front teeth...that's all I want for Christmas... ;-)

Cheers,

Scott..

S. Anderson said:

"Carl Fogel" <[email hidden]> wrote in message >

Quoted message said:

It lets you set the number of front teeth

I'd give anything for my two front teeth...that's all I want for Christmas... ;-)

Dating yourself with that one!

Bill "not dinner and a movie, either" S.

"Raymo853" <[email hidden]> wrote in message news:<[email hidden]>...

Quoted message said:

Gear ratios calculations are better for some situtations, however, I am concerned about MPH at a
certain RMP while considering cassette choices for an upcoming race.

Gear inches X Cadence X .003 = speed in MPH

For instance, a 112 inch gear at 90 RPM yields 30.24 MPH .

The constant is actually .0029714... but 3 digits after the decimal point should be good enough.

Jeff "memorized pi to 20 digits when I was in grade school" Wills

Quoted post said:

Originally posted by R15757
Carl fogeled:

<< Dear Raymond,

Here's an ancient spreadsheet that should import into almost any modern spreadsheet:

home.comcast.netGear3.wk1Open ↗

It lets you set the number of front teeth and the rear wheel diameter and shows RPM versus MPH for a
wide range of rear cogs.

Here's where you can see roughly the same question, with a few pages of output that might be all
that you want:

groups.google.comgroupsOpen ↗
g.google.com&output=gplain

Good luck,

Carl Fogel >>

Carl, I'm surprised at you. No mention of crank length? I thought we were all getting behind Sheldon
in the Real Gearing Revolution.

Robert

Dear Robert,

You are old, Father William, the young man said . . .

Actually, all that's needed to calculate MPH is crank
RPM, gear ratio, and rear tire size.

That is, for a given tachometer reading, the length of
the crank doesn't affect the speedometer reading.

The original poster wants RPM and MPH in order to
fiddle with his gears, not his crank, so RPM and MPH
are what he gets.

I'm graciously assuming that either the original
poster uses the only correct crank length (175mm,
like mine) or else is willing to risk certain death.

Live and let live,

Carl Fogel

-----BEGIN PGP SIGNED MESSAGE-----

_ I was messing around with gnuplot and came up with this style of plot for doing gear comparisions.

stanford.edugear.pngOpen ↗

_ It's a plot of MPH vs gain ratio with the error bars representing a range of 60 - 100 rpm. I find
it a very handy way to compare things, but I know from past experience that what makes sense to me
often doesn't for others. So if there was a tool to generate these plots would you use it?

_ Booker C. Bense

-----BEGIN PGP SIGNATURE----- Version: 2.6.2

iQCVAwUBQEaEcWTWTAjn5N/lAQGG+QP/ZHIRTiRMtOJ6Io0QbR6ZYa9xTAnhhQWh
jrkBDpR+h4k6xI4vlXGH5jOLYMIvN0htu4uGycy0JXzc+PnK5xyAE1dMD24M8XMp
Y8MEjPZSXStar5a/ArSUbdSNVF7MiulcpHz3jEvHslSAVTFnI1Y+rPE12ixeLPjE +/81gyNiTXs=
=8oi8
-----END PGP SIGNATURE-----