I'm not too sure about skateboarding, but for in line skating, that isn't exactly correct. All wheels - for both skates and skateboards - go by XXmm (this is the diameter of the wheel) XXa (this is the "durometer" of the wheel which determines how soft or hard it is going from a scale of 0-100 with 100 being the hardest). Soft wheels are the exact opposite of what you'd want to use on rough terrain as the wheels will get chunks in them. Soft wheels (anything under 78a) for smooth terrain, hard wheels for rough terrain (like old asphalt).