The single ring piston is considered to be the Wiesco "race" piston. ther is less drag between the cylinder and ring, upside is maybe a moderate performance gain when new, keep in mind as they wear performance drops. I run the single ring piston in my 06 kx 250, but I also have a deal with Wiesco so I change pistons pretty frequently. If your not racing I would go with the 2 ring piston, you won't know the difference.