Most adult-size bikes sold these days are equipped with multi-speed gearing. Usually, that takes the form of a system with derailleurs that move the chain from one combination of front chainring and rear cog to another. Occasionally, you may see a bike with internal hub gearing, a single-speed bike without gears, and even more rarely you may encounter a bike with what’s called a fixed wheel, meaning the cranks turn as long as the bike is moving, and there’s no choice of gears either.
In this section, you’ll learn how to use the gears on a bike with derailleur gearing. Except for the technical explanation of how derailleur gears work, what’s covered here regarding gear selection also applies to bikes with hub gearing.
FIG. 1. Typical 24-speed derailleur system on a modern mountain bike. There
are three chainrings on the right crank in the front and eight cogs on the
freewheel in the back.
Both types of gearing have gone through a veritable revolution during the last 20 years. As recently as 1980, the norm for a bike with derailleur gearing was the “ten-speed,” on which you had the choice between 2 chainrings at the cranks and 5 cogs at the rear wheel. And those things did not shift without some sophisticated skills on the rider’s part. Today, most bikes sold are equipped with 18- or 24-speed gearing, with 2 or 3 chainrings in front and 8 or 9 cogs on the rear wheel. What’s even more significant, the modern derailleurs are much easier and more predictable in their shifting behavior than the old ones were.
The Parts of the Derailleur System
Mountain bikes, road bikes, hybrids, and touring bikes invariably use the derailleur gearing system. It’s controlled by shifters, usually mounted on the handlebars, which operate the derailleurs via flexible control cables. The right shifter controls the shifts with the rear derailleur; the left one, the shifts with the front derailleur. Usually, the shifters are indexed, which means that there are definite click stops for each of the gears, making it much easier to shift than it was on bikes built before about 1986.
In the front, there are usually two or three different size chainrings. In the back, most of the newest high-end road bikes have 9 cogs and mountain bikes have 8, while older and simpler bikes may have anything from 5 to 7 cogs to choose from. The different sizes of chainrings and cogs are defined by the number of teeth around their circumference. Front chainrings have anything from 28 to 56 teeth, while cogs can have anything from 11 to 34 teeth, depending on their position in the sequence, and the type of bike, On mountain bikes, a typical setup will have chainrings with 24, 34, and 44 teeth, and cogs ranging from 11 through 28 teeth. A road bike typically has chainrings with 42 and 52 teeth and cogs ranging from 11 to 24 teeth, while hybrids and touring bikes typically use a configuration that is similar to the ones used on mountain bikes.
The highest gear will be the one on which the biggest chainring is combined with the smallest cog; the lowest gear combines the smallest chainring with the biggest cog. All other combinations fall somewhere in between.
Gearing Theory
The different gears are selected to compensate for variations in terrain. If you use the gears properly, you can maintain a fairly constant pedaling rate of perhaps 80 rpm (revolutions per minute) and a fairly constant pedaling force, while varying the bike’s speed to match the difficulty of the terrain. Going downhill, select a high gear, which translates to a high riding speed for a given pedaling rate. Uphill, select a low gear, resulting in a lower riding speed at the same pedaling rate, keeping the force you have to apply to the pedals comfortable.
The easiest way to think of your gear is the distance you travel per crank revolution. A high gear lets you cover a greater distance for each crank revolution, making it faster and harder to push. A low gear lets you cover less terrain, making it slower and easier.
To be able to compare just how high or low a gear is, gear ratios are expressed by what is called a “gear number” in inches. This figure represents the theoretical wheel diameter of an equivalent directly driven wheel. The number can be read off from a chart that’s available at most bike shops, or it can be calculated as follows:
Gear number in inches = (wheel diameter in inches) x (teeth on chainring)/(teeth on cog)
As an example, if your mountain bike with 26-inch wheels has a biggest chainring of 44 teeth and a smallest cog with 11 teeth, the resulting highest gear is 26 x 44/11 = 104 inches. If your smallest chainring has 24 teeth and the biggest cog also has 24 teeth, your lowest gear will be 26 x 24/24 = 26 inches.
FIG. 2. Gearing combinations. Combining a big chainring with a small cog
results in a high gear; a small chainring with a large cog gives a low gear.
FIG. 3. These are the crossover gear combinations. Don’t use them, because they increase chainring and cog wear and cause poor shifting.
Gearing Practice
Don’t cross-chain; keep spinning; and change to the appropriate gear before it’s too late. That is the short course in gearing. Now for what that means:
Don’t cross-chain means that you should not use the gear combinations on which the chain runs from one extreme position in the front to the opposite extreme position in the rear. Take a look at your gearing setup. In the front, the smallest chainring is on the inside, the biggest on the outside. In the back, the smallest cog is on the outside, the biggest on the inside. So avoid running the chain across from the small (inside) chainring to the small (outside) cog, or from the big (outside) chainring in the front to the big (inside) cog in the back. In those gears, the chain would be twisted sideways too far and that causes excessive resistance, noise, and wear. This may also overextend the rear derailleur, causing it to fail and making the chain skip.
FIG. 4. In the low gear (top), one crank revolution takes you forward by
a short distance. In The high gear (bottom), each crank revolution takes
you a long way requiring a greater effort but resulting In a higher riding
speed.
Put the bike up on a stand or support it any other way with the rear wheel off the ground, while the cranks are free to turn. Turn the cranks, and keep turning them. Shift with the right- hand shifter while looking at the rear derailleur. Note when the derailleur engages the biggest cog (low gear), and when it engages the smallest (high gear). Repeat until you remember what’s what. Then do the same with the left-hand shifter, while watching the front derailleur. Practice until you know when the front derailleur puts the chain on the biggest chainring (high gear), and when on the smallest (low gear). Make a mental note of the shifter positions that correspond to the two cross-chain combinations, big-big and small-small, and remember not to use them when you’re out riding the bike.
Now take the bike out on the road—better yet, on an empty parking lot. Ride it around and repeat all those shifting combinations. Note also that shifts are smoothest if you keep pedaling but reduce the force on the pedals while shifting.
Finally, take the bike into hilly terrain. Start off on level ground, selecting an intermediate gear ( For example, an intermediate cog in the back with the middle chainring on a mountain bike, or the smaller of the two chainrings on a road bike). When you’ve gathered speed, shift up a notch with the right shifter (rear derailleur), and another notch. Then also shift with the left-hand shifter (front derailleur). When you go uphill, shift down; when you go downhill, shift up.
Now that you at least know what to do, start working on developing a feel for just when to do it. Try to maintain a relatively high pedaling rate (at least 60 rpm, preferably more, under most circumstances short of a very steep climb). When the bike starts going uphill, shift before you’ve lost momentum and start to slow down. Practice consciously until you feel you’ve mastered the trick, and you’ll be a much more competent cyclist. You’ll enjoy your riding and you won’t tire as fast as riders who have not practiced shifting.