More than any other question, cyclists want to know about bicycle gearing.  We have your answers here.

This article originally appeared in Adventure Cyclist, membership magazine of the Adventure Cycling Association, in 2002.  Join Adventure Cycling at adventurecycling.org.

Cycle Sense

Gearing 101

For those of you just tuning in, this is what gearing’s jargon means

By John Schubert

A few months ago, I went to buy my son skiis for Christmas.  The store clerks showed me several skiis, and then so completely baffled me with their clumsy attempts to describe the differences that I did what any right-thinking parent would do:  I got the kid a stereo instead.

The experience was a reminder:  it can be frustrating to learn a new activity.  Your questions are met with jargon meant to impress, or well-meaning explanations by people who don’t know how to explain stuff very well.

So when I got a batch of letters from ACA members asking basic gearing questions, I was reminded of the simple truth:  the vast majority of U.S. people, including elite Ivy League graduates, doctors, lawyers and even economists, do not know the jargon of bicycle gearing.

Therefore, today I’m going to bring you up to speed on what the terminology means.

The nomenclature of bicycle gearing is different from the more familiar nomenclature of automobile gearing.  In car transmissions, gearing is expressed as a ratio, with the understanding that it’s always some number compared with one.  A car’s gear ratio of “2.84” means “2.84:1.” It means the car’s engine turns 2.84 times for every time the drive shaft turns once.  Bicycle gearing is expressed in a single number that is not a ratio, and that number is “gear inches.”  Gear inches is usually a two-digit integer, and the useful range of gear inches is, roughly speaking, anywhere from 15 to 120.

(The French have a different number they call “development.”  But I’m going to ignore France’s way for today.)

The concept of gear inches dates back to “ordinary” or “high wheeler” bikes.  Those bikes were sold by wheel diameter, and the larger the diameter of the big wheel, the farther you’d travel with each turn of the pedals.

Then came the “safety” bike with its two smaller wheels, and now the wheel diameter sounded like it would slow you down.  If you were accustomed to the speed of a 45-inch ordinary, a 25-inch wheel would sound something of a bringdown.

So the makers of safety bikes responded by reminding the customer that their bikes had gearing.  For example, a 27-inch wheel diameter bike with a 2:1 gear ratio would take the rider as far on each pedal stroke as an ordinary with a 54-inch wheel diameter and 1:1 gearing.  They said the bike had 54 gear inches.

This is the nomenclature that survives with us today.

So every time you want to know the gear inches of a particular gear, you do long division.  Count up the teeth on the chainwheel in use. Count up the teeth of the rear cog in use.  Divide the chainweel by the cog.  Then multiply that number by the rear wheel diameter.  (Don’t bother measuring your exact wheel diameter.  It’s customary to round off to 27 inches for a road bike or 26 inches for a mountain bike.)  Then round this number off to the nearest integer, just to keep things simple.

Your bike probably has two or three chainwheels (front sprockets) and anywhere from five to 10 cogs (rear sprockets).  (The word “sprocket” is ordinarily not used when talking about bicycle parts.  We use the words “chainwheel” and “cog,” so the listener knows whether we’re talking about front sprockets or rear sprockets.)  Every combination of chainwheel and cog is a possible gear for your long division work.

Some of you will already have dashed out to your garage, and made a little chart of the gearing on your bike(s).  A gear chart can be quite handy for correlating the numbers we’re talking about to the shift lever positions on your bike.

Here is a gear chart showing gear inches for all the gearing combinations on a Bruce Gordon “Basic Loaded Touring” bike with 26-inch wheels.  The chainwheels are 22, 32 and 44 teeth (across the top row) and the cogs are from 11 to 32 (down the left column):

   22 32  44

11 52 76 104

12 48 69  95

14 41 59  82

16 36 52  72

18 32 46  64

21 27 40  54

24 24 35  48

28 20 30  41

32 18 26  36

Charts like this are a veritable Rosetta Stone to some folks.  They help you understand gearing so well that you can’t wait to type one up and tape it to your handlebar stem.

These same charts are anathama to some others, who dread having their overly helpful spouse try and explain the stupid chart one more time.  It’s all about different learning styles.

I don’t care which group you fall into, but I do care that you understand the concept behind the chart so that you can (a) answer your own questions about gearing and (b) shift your bike fluently so you’re always in the best gear for the next pedal stroke.

(A note to the statistics police:  when you chart your gears, always round the result off to the next integer.  Really, that’s close enough.)

Now you need to know how to set the gear-inch numbers in perspective.  Here’s my list of approximate uses:

18 to 25 gear inches:  steep uphills with touring gear.

25 to 30 gear inches:  steep uphills unloaded.

30 to 40 gear inches:  moderately steep hills.

40 to 50 gear inches:  moderate hills

50 to 60 gear inches:  mild hills

60 to 70 gear inches:  very slight hills

70 to 80 gear inches:  flats

80 to 90 gear inches:  downhills

90 to 100 gear inches:  steep downhills

100 to 110 gear inches: very steep downhills

over 110 gear inches:  warning:  gears like this are hazardous to your knees.

People often ask whether a particular bike has good gearing for touring.  The Bruce Gordon bike I mentioned above is about as good as it gets.  The gears are closely spaced together, so you aren’t left wishing for an in-between gear.  (Well, the gap between the 12- and 14-tooth cogs is a bit big.  That is this gearing’s only significant deviation from the ideal.)  The low gear is plenty low enough and the high gear is plenty high enough.  You can do most of your riding on either the middle or large chainwheel, reserving the small chainwheel for genuinely big hills.

Sadly, if you buy a less-expensive production touring bike, you might not get gearing as good as the Bruce Gordon’s.  Thanks to the, um, biases of a major component company, we sometimes see chainwheels of 30/42/52 and an 11-26 cog cassette.  This gives you a not-low-enough low gear of 31 gear inches and a wreck-your-knees high gear of 128 inches.  For real touring, you’ll want to swap the small chainwheel for a 26-tooth, and  you may also want to swap the rear cog cassette for one with a larger cog (depending on what your rear derailleur can handle).  If you can get rid of the knee-busting high gear in the process, so much the better.

I believe gears above 90 to 95 inches are of very limited use for loaded touring.  I like speed, and I’ve done bike racing, and racing is much better without panniers.  And touring is much better without undue emphasis on speed.

For loaded touring, your lowest gear should be, oh, 18 to 25 inches.

Next question:  what should the gaps between gears be?  My answer, which not everyone agrees with: smaller than they usually are.  Ideally, your gears would be about ten percent apart from each other.  How important this is depends on the kind of riding you’re doing.

Tourists riding loaded bikes on long, constant grades benefit greatly from closely spaced gears (and the technique to use them).  When the grade is constant, you’ll settle into a groove, and if you can make minor adjustments in your gearing, you’ll ride better.

When you ride on terrain where the grade changes constantly, you’re less likely to ever get a chance to settle into such a groove for any appreciable length of time.  Under these conditions, gears spaced 15 or 20 percent apart are okay.  

How do these theoretical requirements square with what’s mechanically possible, or commercially available?  The answers are “pretty well” and “well, okay.”  In this era of ten-cog rear ends, that’s enough sprockets to have the gears well spaced and cover an adequate range.  But it doesn’t always work that way, because several of those cogs are wasted providing an assortment of too-high gears.  Count up the teeth on your bike and do the math.  See where you stand.