A mountain bike may be used for everything from gravel roads to steep, goat-path singletrack, depending on the type. The more difficult the trails, the more rear suspension you should have. Bikes having 27.5-inch wheels may help smaller riders. Those with larger wheels may find them better suited for more challenging terrain. Mountain bikes are excellent vehicles for getting around town or city streets. They are also useful for hiking because of their small size and light weight. You can take your mountain bike on trains and buses if they have parking spaces for bicycles. Some cities and towns require that you register your bicycle with the police department, so check with them first to make sure that it is allowed in neighborhoods you plan to visit. Mountain bikes are very popular among adults who want to get some exercise but don't feel like driving a car every day. They're also useful for people who live in rural areas because they provide easy access to places where other transportation isn't available. Mountain bikers often ride on paths known as "trails" which are made up of dirt or paved road surfaces that connect up with each other or with the main street network. These paths usually run through parks or along railroads, but they can also go through residential areas or farmland. Mountain biking is becoming increasingly popular among children as well.