On very light frames only, unsupported thin frame walls can buckle slightly under high loads, reducing strength and stiffness. Light weight carbon fibre bulkheads at strategic locations (down tube at head tube, seat tube at top tube, above the bottom bracket shell) brace the walls, boosting stiffness while adding less weight than would be needed to thicken the walls. Net result: 2.2 grams lighter and 6% stiffer, as seen in the RCA. Frames with sufficiently thick walls wouldn’t benefit from adding bulkheads, so bulkheads are currently found in the R5ca, RCA and S5VWD only.