Honda Explains the 2013 CBR600RR Big Piston Fork
The BPF system is based on advanced engineering with race-focused performance, but the basic principle behind it is quite simple: the bigger the pressure-bearing area, the less pressure is needed to obtain a specific damping force.
Unlike the previous forks which used a cartridge to regulate the oil flow, the Showa BPF relies on a single piston to do this. The damper piston is around 3.5 times as large as the previous cartridge system, providing better damping with noticeably less oil pressure, and granting the fork a much smoother, more sophisticated operation.
This can be noticed in the improved, quicker response and a smoother action, especially in the initial travel of the system. With the lower pressure in the fork, oil can flow more easily, offering smooth reaction in both damping small and bigger bumps, thus creating a feeling of grip and traction for the front wheel, and enhancing the rider confidence in various scenarios.