I HAVE A ALL STOCK HONDA 400EX { 2000} . I weigh 240lbs and wanted to know if replacing the front sprocket would be enough to see a noticeable increase in all out speed. 5th gear just doesnt have enough top speed for me. Any recoemendation on how many tooth front sprocket may achieve this and how many tooth is the stock front sprocket suppose to be ? I figured changing the front sprocket would be the easiest and least expensive option to try 1st to get more speed.

 

Going up 1 tooth on the front equals around minus 2.7 teeth on the rear.
Stock front sprocket is 15 teeth. You may get 4-5mph more out of a 16 tooth sprocket.