A gear is a component of the drive train of your bike. Gears, simply put, are pulleys that help you transfer power from your legs, through the pedals and cranks, then through the chain, and eventually to the rear wheel. A single-speed bike only has two gears — one attached to the crank and one attached to the rear wheel. Bikes with shifters and derailleurs (more on that later) have one or more gears attached to the crank and multiple gears attached to the rear wheel. On both types of bikes, a chain connects the gears on the crank to the gears on the rear wheel. Gears have a cogged outer rim, which meshes with voids in the chain to help you transfer power efficiently.
A Quick Summary on Shifting
1. To shift onto a different chainring/gear up front, use your left shifter.
2. To shift one of the rear gears (and how you’ll shift most often), use your right shifter.
3. For smoother shifting, pedal lightly while using the shifter. Don’t back-pedal.
4. If you’re pedaling too fast, and there isn’t enough resistance, shift into a harder gear. You’ll also go faster.