What about rims with a black-painted groove in the center of the machined braking surface? My Velomax Circuit wheels have these, as well as another set of Alex rims. But, no instructions or warning came with the wheels, so I have no idea if the groove is intended to be a replacement wear indicator.
If these are wear indicators, does the manufacturer specify that the rims must be changed when the grooves disappear? Or, is it safe to continue to run them until they appear concave?
Would hate to toss out a good wheel early, but waiting until the tire bead pops off doesn't seem to be a smart strategy either