A quantity to measure whether brakes should be repaired

Suppose you can record some suitable parameters each time a driver uses the brakes of a vehicle (assume it’s a heavy truck if necessary). Is there a reasonable formula for a dimensionless quantity $Q$ such that, say if for example $Qin [5,10]$ in most tests, then the brakes seem to be working properly, but otherwise should be considered to be repaired?

Any help appreciated!

(I just found http://www.engineeringinspiration.co.uk/brakecalcs.html#bf2 and will have a look at it as well.)