When you shift gears in your car (assuming you have a manual transmission), You don't have to search around for the right gear because you know where each gear is. So why search around for the right one on your bike? With a little time you can know exactly where each "speed" is, so you can shift directly to the one you want.

Figuring out your gearing is not as hard as you may think. It doesn't take a PhD in engineering, Goodness knows I don't have one. Just some basic math. Here's how you do it.

Start by finding out the number of teeth on each cog, and each chainring. Write these down. Now, use this formula to find out the "gear inches" for each combination;

Front/Rear x Wheelsize

"Front" is the number of teeth on the chainring being used.
"Rear" is the number of teeth on the cog being used.
"Wheelsize" is the diameter of the rear wheel.

When you have all the gear inches for each combination, put them in order from the lowest number to the highest number. Be sure to put the chainwheel/cog combination next to each one.

Now, you need to create a shifting pattern, so you can see how each combination stands in relation to the others, and how to get to them. To do this, make a simple table. Here's what mine looks like:

__|26|44|48
34|01 04 05
28|02 06 07
24|03 08 09
20|04 10 11
17|XX 12 13
14|XX 14 15
12|XX 16 17

The numbers are not the actual gear sizes, they are just the order, from lowest to highest. This is just an example, yours will probably look different. Now, lets see how this works.

The numbers along the top are the chainwheels, the numbers down the left side are the cogs. If you draw an imaginary line down from the chainring you're using, and draw another imaginary line across from the cog you are using, the point where the two lines cross is the gear you are in.

The "X's" in the three bottom places in the 26 collumn are there because those combinations can't be used. The chain would rub on the next larger chainring or cog. That's O.K. because the gear inches those three create are almost identical to others in the pattern.

You may also notice that there are two 4th gears. This is because these two combinations are almost identical. This is almost unavoidable, but in this case it's considered tolerable because the gears in the 26 collumn stand apart from the others. They are the super-low gears used on really steep hills. The gears in the 44 and 48 columns are for less radical terrain.

This is called a "Half-step + Granny" combination. The super low gears in the 26 chainwheel are called "Grannys" because supposably they make clmbing so easy even your grandma could do it ;-3). The 44/48 collumns are called a "Half-step" because shifting from the 44 to the 48 chainring changes the gear inches only half as much as changing from one cog to the next

The advantages of this combination are that you get a lot of different gears, and the pattern isn't too difficult to learn and use, especially now that almost all bikes have the shift levers on the handlebars. Here are a couple of other patterns:

~ Crossover ~

__|Sm|Lg
Lg|01 XX
2_|02 XX
3_|03 XX
4_|04 05
5_|XX 06
6_|XX 07
Sm|XX 08

This pattern is known as a "crossover" because you cross over from one chainring to the other at the center cog. Although you could use the other combinations, they are all duplicates of other gears.

Why use a pattern with so few different gears? the reasons are because it's simple. All the low gears are on the small ring, all the high gears are on the big one. And you don't have to shift both the front and back derailleurs to go to the next gear. This pattern is most popular with racers, who used to have the shift levers mounted on the down tube of the frame. It made fast shifts easier. It isn't usually used with a triple crankset (which also makes it a lighter) because it offers a good wide range by itself. That's why there are only two collumns. Racers don't need real low gears anyway. They are strong enough to climb without them.

~ Alpine ~

__|Sm|Md|Lg
Lg|01 05 07
2_|02 06 09
3_|03 08 11
4_|04 10 13
5_|XX 12 15
6_|XX 14 17
Sm|XX 16 18

"Yee gads!", I hear you cry. Well, believe it or not, this is the most commonly used pattern for triple cranksets these days.

Since the half-step by itself does not provide a very wide range, it was first used by touring cyclists who wanted a wide range of gears (from very low to very high) but didn't want, or couldn't afford a triple crankset. But like the half-step, almost all the gears are different. It provided a happy medium.

The complexity wasn't as much a problem for touring cyclists because they didn't have to worry about fast shifting as much as a racing cyclist. The pattern shown is a triple because it's used mostly on mountain bikes which need the super-low gears the middle gear wouldn't be able to provide if it was the smallest chainring.

Which is best? depends, which is best for you? Gearing is one of the most personal things you can do to a bicycle. You can even customize the gearing to suit your own individual needs. Although this has gotten very difficult to almost impossible to accomplish in recent years, because many modern cogs are only compatable in certain combinations. Some manufacturers have even gone as far as to stop selling individual cogs. Selling instead only complete sets which cannot be disassembled or customized.

You can still choose which chainrings you use, however. And with this limited flexability come up with a cogset/chainring combination which gives you something at least close to what you need,. If your willing to take the plunge.