On Saturday, September 28, 2019 at 9:06:57 AM UTC-5, Frank Krygowski wrote:

Is there a rule of thumb for minimum safe rim thickness at the braking surfaces?

I've worn a couple rims to the point where they have begun to show cracks along the braking surfaces. The brake on the affected wheel would "pulse" slightly because of the wide spot. The brake surface was between 0.5 and 1.0mm thick. Most of the new rims I've measured have 1.4 to 1.6mm of brake surface thickness. So I'd say when the thickness reaches around 1.0mm it would be time to start looking for a brake pulsation and planning a rim replacement at a convenient future time.