Selecting the right size dirt bike is essential to having safe and enjoyable experience. If you don't enjoy riding your machine, guess what? You won't ride it. There are so many factors that go into this important decision, including age, height, weight, and experience level. Other important factors include the type of riding you will do and you're riding style. Pure motocross bikes and pure trail or enduro bikes differ greatly (a topic for another time), so consider the type of riding you intend to do and select a bike that fits that style. The same is true for choosing between a two-stroke and a four-stroke. Each behaves very differently and each has its pros and cons.