Originally Posted by
operator
There is no such hole on the bontrager raace x lites. There is a hole on the side of the rim which is nowhere near the braking surface that is water drainage -> I'm looking at a set right now.
And to answer the OP - the concavity of the braking surface gives you a rough idea of the state of wear.
Can you measure the flats on the sides of the rim - where the brake-pads contact? Curvature in this could be a good indicator for these then. Unless (I hate...) Bontrager made 'em curved in the first place.