After 1000 miles on my bike I went to the 19th tooth...Of course to bring the highway RPM's down and save on wear and tear, fuel and oil useage, but also it keeps you from trying to shift into that elusive 6th gear. I absolutely love it (4500 miles later) and will never change! I ride a lot in the city and a lot on the highway to and from work. I have also been in the mountains of Arizona, California and North Carolina with no issues looking for power. My opinion is to go with the 19 tooth...But like everything else, each's own! Good luck, welcome to the site.
