These shimano option are 11sp compatible wheels which means and thanks to the supplied spacer you can use these on either 10 or 11 speed shimanosram systems carbon tc 35 fast forward ffwd use high tensile tc 35 carbon for the majority of the lay up this gives the rim a very high strength with sufficient stiffness to cope with hard application of the wheels so rather than use a stiffer but more brittle carbon type they chose durability over ultimate stiffness in some lay ups they