Redesigned super-strong BACKSIDE bulkheads are narrower to go the hands more into centerline to produce more traction and also to provide an even more substantial variety of track width modification. The bulkheads have in reality an excellent fit towards updated differential plus they are strengthened to improve the reliability. The XB4 bulkheads allow super-fast & simple diff trade and servicing by dismounting just 4 screws through the front part from bulkhead and base from the framework. This super-fast diff access can be had at both front & back. The bulkheads have actually in fact minimized ball-bearing play, causing increased gear teeth lifespan and minimized gear stripping.