Bikes have two sets of gears. The first set is by the crank, or the arm to which the pedal attaches. The second set is on the back wheel, right in the center of the wheel, on the same side as the crank. The back gears are also called cassette cogs. The chain wraps around the gears, or sprockets, on these sets and controls pedaling difficulty and cadence. The chain moves between the gears when you change the position of the indicator on the shifter, which moves the front and rear derailleurs.
Count and Multiply
Count the number of gears by the crank. You’ll see one, two or three gears. Then, count the gears on the rear wheel. You can have anywhere from one to 10 on here. Multiply the front gear number by the rear gear number to get the number of speeds. For example, if you have two front gears and five back gears, you have a 10-speed bike. If you have one front gear and three back gears, you have a 3-speed bike. If you have three front gears and nine back gears, you have a 27-speed bike.
If you see only one front gear and one back gear, you have a single-speed bike. These do not need shifters on the handlebars because there’s nowhere for the chain to go.