I heard on the Fredcast TDF recap this morning that in the old days (unsure when) the TDF powers-that-be (were) categorized all the climbs using a little Cintroen car. If they could get up the hill in 4th gear, it was designated category 4. If they had to downshift to 3rd to make it, it was deemed a Cat 3, and so on for Cat 1 and Cat 2. If the poor little car couldn’t make it to the top in 1st, it was deemed HC. Unsure of the accuracy of this, but it’s kinda interesting.
Sounds like a great way to categorize climbs!