A bicycle is a two-wheeled steerable machine powered by the feet of the rider, turning pedals connected to cranks that rotate a chain and drive the rear wheel. It is the only human-powered machine that can maintain a constant speed over time without requiring the effort of walking or running. Bikes are a popular mode of transportation for commuting, fitness, and recreation, and have helped transform towns, cities, and countries around the world into healthier, more vibrant places.

The word “bicycle” was coined in the mid-1800s, although earlier terms for two-wheeled vehicles include velocipede de pedal (speedy foot-powered vehicle), dandy horse, hobby horse, and pugilistica (pugilist). Today’s bike designs and materials continue to evolve from those early days of wrought iron frames, steel wheels, and wooden handlebars. Today’s bikes are lighter, faster, more durable, and easier to maneuver than ever before.

Road bicycles are designed for fast, long distance rides on paved roads. Their lightweight frames are typically made from carbon fiber or aluminum alloy to keep them light and fast, and they have gears that allow you to ride hills easily. They also have a narrower saddle than a racing bicycle (you ride more quickly when you’re leaning forward).

Some people use road bikes to compete in races called criteriums, stage races, and one-day classics (like the Tour de France). These are short, fast-paced races on closed-loop courses that test your endurance and technical skill.

Many of today’s hybrid and comfort bicycles feature suspension forks that compress to limit the jarring impact of bumps, cracks, and other obstacles that you may encounter on cycle paths and bridleways. They also have wider, softer tires that are more capable of handling rough surfaces and insulate you from the jolts of uneven ground.

If you plan on using your bike to commute or do other longer rides, look for a model with the mounting points needed for pannier racks. These can be used to carry extra clothing, water, and food for longer trips. Some models even come with pannier racks already installed.

When shopping for a new bicycle, the first step is to determine your ideal frame size. Stand over the top tube of the bicycle and see whether you can place your hands flat on the ground with a slight bend in your knees. Then, measure your trunk length (also known as sitting height) to find out your torso length and reach.

Kids’ bicycles have shorter and lighter overall frames, smaller parts, and quality components that are sized appropriately to fit children’s bodies. Look for names like Shimano and SRAM that are synonymous with quality. In addition, make sure the bike weighs relatively little—remember that proportionally a 60- to 70-pound bike feels much heavier to a kid than it does to an adult. And lastly, look for components that are easily accessible and operate with minimal hand force. In general, it’s a good idea to shop with a knowledgeable professional who can help you select the best bicycle for your riding needs.