Star Ratchet VS Ratchet EXP!
The star ratchet system requires two conical springs to push two ratchets against each other. The teeth of ratchets are well oriented so that they engage in one direction while sliding over each other with the teeth tip to tip when freewheeling. Ratchet EXP is the 2.0 version of this simple, elegant, and time-tested system.
The key improvement of the Ratchet EXP system is fewer moving parts. It removes one spring by fixing the inboard ratchet into the ring that threads into the hub shell.
The reduced number of components contribute to weight loss but also the increased axle stiffness as the bearing width is maximized. The drive-side bearing moves outboard and sits inside the threaded ring. EXP freehubs are in both regular bearings and ceramic. 180 hubs come with ceramic and 240 come with regular stainless steel bearings but they are interchangeable
With the inner ratchet fixed and easily aligned with the outboard ratchet, the new system has faster full engagement (both ratchets are 100% engaged). The surface pressure is reduced so there will be less wear between parts. The hubs feel really solid under power because there are no pawls flexing as with a traditional design.
For the old 240, there are three ratchet choices: 18T, 36T, 54T. The 240 EXP, however, comes in with 36T (10° engagement) as a standard, with an eventual 54T option if you require it. According to DT, the 36-tooth option achieves a good balance between these three factors: points of engagement, weight, and reliability.