Go here.
http://www.sprocketspecialists.com/SprocketOptimizer2.aspx
Enter the information in the top section, particularly where it says front to rear axle distance. Put in the distance from the front sprocket (drive shaft) to the rear axle (taking into account the 10" extension). That should do the trick.
http://www.sprocketspecialists.com/SprocketOptimizer2.aspx
Enter the information in the top section, particularly where it says front to rear axle distance. Put in the distance from the front sprocket (drive shaft) to the rear axle (taking into account the 10" extension). That should do the trick.