On a 1990 Fxlr the rear pulley has a number of teeth on it. How many pulleys will work within the spec of the diameter of the stock set-up that are available. I have heard of a 65 teeth and a 70 teeth pulley. Being said that it has a five speed tranny, is that considered a low ratio to the five speed tranny of the two pulley,s. To get better performance and mileage, what would be a better choice of the two pulleys.