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Path: utzoo!watmath!clyde!burl!ulysses!harpo!decvax!ittvax!dcdwest!sdcsvax!sdcrdcf!hplabs!cygnet!kwd
From: kwd@cygnet.UUCP
Newsgroups: net.bicycle
Subject: Re: Gear Ratios
Message-ID: <486@cygnet.UUCP>
Date: Wed, 16-May-84 15:00:54 EDT
Article-I.D.: cygnet.486
Posted: Wed May 16 15:00:54 1984
Date-Received: Fri, 18-May-84 00:06:36 EDT
References: <1474@sdccs6.UUCP>
Organization: Cygnet Systems -- Sunnyvale, CA
Lines: 43

[]
>> In some of the articles in this group people talk about 33 inch gears or
>> 80 inch gears. Just what exactly is meant by this, and how is it
>> computed.
>> 
>> 				Christopher Latham
>> 				U.C.San Diego
>> 				Dept. of Applied Mechanics
>> 				and Engineering Sciences
>> 				..sdcsvax!sdccs6!ix1037
>> 
------------------
You mean you really don't see how these folks are getting around
on 80 inch gears!!  Actually the term is "gear inches" and it is
basically a measure of "how hard you have to pedal".  Formula is

	Gear Inches = ( F / R ) * W

	F = Number of teeth on front sprocket
	R = Number of teeth on rear sprocket
	W = diameter of real wheel in inches (typically 27)

Thus if you shifted "to a gear" (I never know what my friend means
when she says she's in 4th gear) such that you were using a front
sprocket with 50 teeth and a rear sprocket with 25 teeth, you would
be riding with (better word?) 54 gear inches.

Typical range available on a ten-speed bike is 40 through 90 gear inches.
Roughly speaking:
	
	90 - moving at a good clip, maybe downhill
	68 - crusing around, flat and level
	40 - uphill, lots of pedalling
	27 - climbing mountains (I have a 28 in front and back!)

I found that graphing out the combinations on my bike helped me use
my gears more effectively... know where the overlaps are, etc.

					Karl Danz
					Cygnet Systems, Inc.

P.S. people who insist on calling front sprockets "chain rings", etc.
     can send all flames to /dev/null.