You'll find this installation one of the easiest things (and best) that you will do for your bike. All the things mentioned (spring compression measurement, shim useage - or not) need to be considered. The spring compression measure (3/8") is the most important part of the installation. Save your shims, at some point in time you will need them. We suggest checking the M6 at about 20k intervals to see if you've had enough chain stretch to warrent adding a shim. You'll see your shifting improve, easier to find neutral, bike will click into gear instead of clunk and DYNO testing has shown both increase in torque and horsepower due to less stress, drag, and friction on your entire primary system. Enjoy the ride.