Rarity?
Thanks for the clarification Dan. I am just going by what I have heard and read, and my own experience. I admit however that I am no where near as well read as you.
Sounds like you and I both have enough experience with drum-brake cars and disc-brake cars to vote for discs. The one thing drums do have going for them that discs don't (except the very complex and expensive airplane-type '55 Chrysler optional disc brake setup) is that drums are self-energising: the way the shoes contact the drum helps force them into harder contact with the drum, reducing pedal effort required for any given level of stopping. Neat trick when everything's in perfect condition and adjustment, but:
1. working against this tendency is that drums expand (get bigger in diameter, move away from the shoes) as they heat up, which doesn't happen with discs, and
2. let there be too much brake dust in the drums and it also means the brakes are much more likely to "grab" (no fun/not safe). This doesn't happen with discs, either.
Funny thing about brakes (also seatbelts): most of the time we don't need much brake and we don't need our seatbelt. Until we do…very suddenly, and very urgently.
(Also, you're right that the performance drop-off with drums is much steeper than with discs. You can build a top-notch drum system, but if you're headin' down a mountain…you still want the discs!)
