Gear Inches

Does anyone have the formula for calculating gear-inches?

Years ago, Bicycling mag would publish a gear-inches chart for each bike
they reviewed--a grid with front & rear gearing along the top and side with
the gear-inches in the center.

I'd like to make a gear-inches chart for my new bike but don't have the
formula. My tires are 700c x 23.

go check out Sheldon's site, or www.fixedgearfever.com

Mike
"Guy Goldich" wrote in message
...
Does anyone have the formula for calculating gear-inches?

Years ago, Bicycling mag would publish a gear-inches chart for each bike
they reviewed--a grid with front & rear gearing along the top and side
with
the gear-inches in the center.

I'd like to make a gear-inches chart for my new bike but don't have the
formula. My tires are 700c x 23.

"Guy Goldich" wrote:
Does anyone have the formula for calculating gear-inches?

Gear Inches = (chainring teeth / cassette teeth) x Tire diameter

To determine your tire diameter, measure the roll out for one revolution,
and divide by pi.

Or check out Sheldon's gear calculator at:

http://www.sheldonbrown.com/gears/index.html

Art Harris

"Guy Goldich" wrote in message
...
Does anyone have the formula for calculating gear-inches?

Years ago, Bicycling mag would publish a gear-inches chart
for each bike
they reviewed--a grid with front & rear gearing along the
top and side with
the gear-inches in the center.

I'd like to make a gear-inches chart for my new bike but
don't have the
formula. My tires are 700c x 23.


There's lots of calculators on the web. Try my graphical
gear calculator...

http://bellsouthpwp.net/k/a/kaeru41/Gearing.htm

"Guy Goldich" wrote in message
...
Does anyone have the formula for calculating gear-inches?

Years ago, Bicycling mag would publish a gear-inches chart for each bike
they reviewed--a grid with front & rear gearing along the top and side
with
the gear-inches in the center.

I'd like to make a gear-inches chart for my new bike but don't have the
formula. My tires are 700c x 23.


That arcane number, which remains a useful number only because we are all
conversant with it, is the equivalent highwheeler size to your geared bike.

Get that by dividing the rear number of teeth into the front and multiplying
by the nominal wheel size, e.g., 52/14*27=100. Put another way, pushing a
52/14 is the equivalent of riding a 100 inch highwheeler bike.

That sort of calculation is very easily done in a spreadsheet. In fact it
uses such rudimantary spreadsheet skills that I use it as a beginner's
example for learning spreadsheet techniques.

Put the front chainwheel teeth in a row, let's say c5 is "50", d5 is "40"
and e5 i s"30".
Then run your rear sizes down a column, such that b6 is "12", b7 is "13", b8
is "14" etc etc.. Enter the wheel nominal size in the corner at b5.

Enter this in cell c6: +c$5/$b6*$b$5
copy that to the remaining cells in your array and hit the F9 (recalculate)
key. It is more readable if you select the array and format display to one
or zero decimals

If you have time to kill and an interest, most modern spreadsheets can
automatically graph your gear range in color!

When I was young this sort of chart (made up by sliderule and typewritten)
could be seen taped to handlebar stems on Sunday morning rides because, as
Sheldon mentioned recently , the gaps in a five speed are huge and
daunting - often worth a double shift to avoid them!

And no, there are no 14-1/2 teeth cogs yet!

In the non-English speaking countries another system is more common,
"development" or how many meters the bike travels per crank revolution.
Campagnolo used to provide nice business-card-sized gear charts of that. My
commuting 60" gear travels about 4.8 meters for example
--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971

"Guy Goldich" wrote:
Does anyone have the formula for calculating gear-inches?


"Harris" wrote in message
. net...
Gear Inches = (chainring teeth / cassette teeth) x Tire diameter

To determine your tire diameter, measure the roll out for one revolution,
and divide by pi.

Or check out Sheldon's gear calculator at:

http://www.sheldonbrown.com/gears/index.html


Precise wheel diameter derived from a rollout?
While that works, using the nominal size, 26" or 27", is close enough and is
the usual factor used in standardized printed gear charts.

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

On Sun, 07 Sep 2003 12:17:35 +0000, Guy Goldich wrote:

Does anyone have the formula for calculating gear-inches?

Chainring teeth/sprocket teeth)*wheel diameter.

--

David L. Johnson

__o | "Business!" cried the Ghost. "Mankind was my business. The
_`\(,_ | common welfare was my business; charity, mercy, forbearance,
(_)/ (_) | and benevolence, were, all, my business. The dealings of my
trade were but a drop of water in the comprehensive ocean of my
business!" --Dickens, "A Christmas Carol"

A Muzi wrote:

"Guy Goldich" wrote:
Does anyone have the formula for calculating gear-inches?

"Harris" wrote in message
. net...
Gear Inches = (chainring teeth / cassette teeth) x Tire diameter

To determine your tire diameter, measure the roll out for one revolution,
and divide by pi.

Precise wheel diameter derived from a rollout?

Yes? ... or yes.

While that works, using the nominal size, 26" or 27", is close enough and is
the usual factor used in standardized printed gear charts.

Lot's of people have computers and don't need/want one-size charts
anymore.

"A Muzi" wrote in message
...
"Guy Goldich" wrote:
Does anyone have the formula for calculating gear-inches?


"Harris" wrote in message
. net...
Gear Inches = (chainring teeth / cassette teeth) x Tire diameter

To determine your tire diameter, measure the roll out for one
revolution,
and divide by pi.

Or check out Sheldon's gear calculator at:

http://www.sheldonbrown.com/gears/index.html


Precise wheel diameter derived from a rollout?
While that works, using the nominal size, 26" or 27", is close enough and
is
the usual factor used in standardized printed gear charts.

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


Using rollout is the only way to get a precise measurement for gear inches.
Close enough won't work as you will likely be off by 2" or so. I found this
out when trying to get qualifying times for track nationals. I figured the
speed I needed to maintain in the gear size I was using (almost all charts
are based on a 27" wheel). All of my gears were 2" off which can mean a few
10'ths of a second over 400 meters...
T