Why Modern Bikes Generally Have Two Identically Sized Wheels. Have you ever wondered why modern bicycles typically have two identically sized wheels? You might be surprised to learn that it's not the case for every bike. When bikes were first invented in the 1800s, they often had three or four different sized wheels on them. Why did things change? It turns out that it was a simple matter of economics and mass production. A bike with two identically sized wheels is easier and cheaper to produce, leading to lower prices and more people able to afford...