The number of wheels will determine the properties of your skate, like speed, agility, grip and stability.
A frame with three wheels makes it easier to learn to steer, to make tight corners or to slalom around pylons. Inline skates with three wheels are agile and light. You can accelerate and gain speed fast, and you will be faster in a short sprint. It also helps you to make a double push. This skill – two pushing phases in the same stride, pushing your leg inside and then outside – is easier to master on an inline skate with three wheels.
A frame with four wheels will give you more speed and stability. You are more stable and will experience more grip when you push off because your inline skates are rolling more straight. More wheels in your frame means automatically that those wheels are a bit smaller, which makes that you’re lower to the ground and you have more balance. More wheels will wear less fast because the friction on the wheels is equally distributed.