What is faster roller blades or roller skates?

If modern inline speed skates are compared to modern quad skates, the former are faster, in part due to the difference in wheel size.

Modern inline skates use 100 - 110 mm wheels, which roll much smoother than the smaller 62 mm wheels on quad skates, and therefore the skater loses less energy.

In the Berlin Skate Marathon, which is open to both inline and quad skaters, very few skaters use quads - and the elite and fastest recreational skaters all use inline skates.