Originally Posted by mrrabbit

Not quite, because that can hide the poor extrusion to the outside circumference....checking ERD all around is important for ERD...but not reliable for judging whether a rim is a good candidate where even relative tension is a high priority - as is the case with multi-speed asymmetrical rear wheels.

Way to home test roundness AND extrusion quality concurrently - which is necessary - is to:

1. Use plastic calipers or metal calipers with jaws taped.
2. Adjust to 1mm more than depth of the rim - assuming no eyelets.
3. Place outer jaw flat against outer circumference of the rim.
4. Brace for side to side motion with caliper arm perpendicular to cross section of rim.
5. Rotate rim through calipers with decent backlight.

If the inner wall varies more than a 1/2 millimeter + or - OR more than 1mm total while rotating rim through - that rim will be a poor candidate for a wheel where even relative tension is an absolute must - typically multi-speed asymmetrical rears or disc fronts.

This is how I separate KinLin MX2Ws and MX2Gs and MX3Ts into one pile intended for single speed or symmetrical wheels and one pile intended for asymmetrical multi-speed rear wheels.

=8-)