Sprint ROAD/TRACK P08 Air Filter
For RS660 & Tuono 660
This is the air filter Sprint recommends for street and occasionally track ridden RS660's. It's polyester filtering media (almost all other filter manufacturers use cotton) is slightly thicker, but still notably less restrictive than cotton and offers better moisture trapping characteristics.
The comparision photo below compares filtering media density between this filter and the Sprint PM176S-FS-85 Race Filter: