carbon kevlar is good, light and good looking but broken easily. pcb fiber has more durability you try this setting upper roller: teflon + high speed bearing for both front and rear lower roller: metal with very sharp edges+standart bearing 0 degre lower roller must be smallest then upper roller ex. up 12mm low 10mm roller must be of the same height between front and rear commonly i use 112mm for many straight track and 113 for many turn/ S turn