In regard to the question on measuring effective rim diameter (ERD), I have in my possession a tool made for this purpose. It is called a RIMometer, and was purchased through Bike-alog. My wife who worked in the industry says it may be avalable through Quality Bicycle Products.
It is simply a white plastic rod about 3mm in diameter with a tapered stop at one end and a sliding sleeve. It is calibrated to measure ERD's from 300mm to 635mm. It is not the fanciest tool around, but seems to do the job.
Sutherland's has a system for the job in their manual which can me done with a tape measure, calipers, and a spoke nipple.
Steve Snider
steve.snider@comcast.net