If you are searching for 6th then as mentioned go up a tooth. I did not think the 06 had an 18. I recently met a guy with an 06 and we discussed sprockets. I assumed he had the 16 like earlier speedies.
I have tried 16, 17, 18 and the belt drive. For my local riding I prefer the 16 but if I could actually ride a highway for any distance without traffic I would use the 17. The 18 is too much for me overall but the parkway ride is great, especially if you can cruise over 75.
