I have V-brakes on my flat bar bike. The rims have a black line that is machined lower than the rest of the rim brake pad contact surface. Is the black machined line a wear indicator? Secondly, are there brake pads that are softer and will wear out faster and the rim slower or is the difference insignificant?
Thanks in advance, Frank.

#1 ... yes, that is a wear indicator. I don't know how much it tells you. If you start seeing a deep concave wear pattern on your rims, they are nearing end of life.

#2 ... I don't know. There certainly are carbon fiber specific pads, but I'm not sure for the standard aluminum rims. Embedded sand, aluminum chips, and etc, will accelerate the riim wear. So,k also finding pads that don't pick up as much debris is good.

Thank you, Frank.