These were vintage (23+ years) rims. I believe wear indicators on rims are more common among modern styles. However, indicators are not really necessary to determine rim wear, they are only a convenient way.

Rims, like brake pads, chains, cassettes/freewheels, etc. are all parts that wear out. If someone doesn't feel qualified to check for dangerous wear on a regular basis (yearly or more depending upon the riding distance), they should consult a mechanic to do so. We forget, since they are so simple, that bikes are machines and they REQUIRE maintenance.


What we can reasonably surmise from the OP.

At 23+ years, the failure is not the result of a manufacturing fault.

With no mention of a collision or impact, on this ride, the failure is not likely the result of such an incident.

Given the above two, and in conjunction with the age, the failure is most likely the result of dangerously excessive wear. A suitable review by a competent mechanic would have been able to ascertain such dangerous wear levels at least for the last year or two.

For those under similar situations the most likely telltale is a noticeable ridge in the rim braking area when you run your finger over it. If you can detect ANY uneven surface, the rim needs to be either replaced, or at least taken to a qualified mechanic to evaluate.