If you're building a custom bike, you really should do your homework beforehand and calculate what your overall gear ratio will be. 

In my personal experience, ratios that have offered the best combination of smooth highway riding and around-town grunt are:

74" motor: 3.23
80" motor: 3.15
93" motor: 3.10

NOTE: These numbers are applicable to big twins, not Sportsters.


Maindrive Cycle gearing calculator

engine sprocket
clutch sprocket
trans sprocket
wheel sprocket

overall gear ratio