Right back shock towers are redesigned allowing for the Horizontal Split Bulkheads (HS), while having denser upper surprise mount functions to obtain more accurate set-up modifications. A large part surprise tower features extra roll center jobs for even more fine set-up modification additionally additional wing mounting functions. Straight back surprise towers are machined from premium-grade 3.5 mm graphite and they're lightweight & strong, with many shock jobs and roll center modification functions Fits XB4'21