Choose wheels for fitness skates according to size, hardness and quiality (very often connected with price) Usually, maximum size of wheels which can be used is stated on the chassis. Wheel hardness affects speed, endurance, ashesion and comfort. Hardness is often marked with number and letter A. The higher the number, the harder the wheel - 85A are then harder than 78A. Top wheels offered by Matter mark hardness with F0, F1,... Hardness is descending from F0 - F0 is then harder than F1, F2 etc. Harder wheels are often faster and durable. On the other hand, softer wheels are less slippery and are also more comfortable on coarse surfaces.