It is the 10% portion that matters. That is why they have a mandatory brake check station, where an attendant uses an IR thermometer to measure brake temperatures. When I was there, a very stinky F150 with Florida plates was ordered into to take a timeout in the cooling off area. When I was there, the road was closed at Devil's Garden, about 13,000 feet, due to snow above. So we hoofed it up to the top. OK, I mismembered the elevation change of the road that killed a Hawaiian member's brakes. It was just 3500 feet. Here is the thread after the second incident: 3,500 foot decent = crazy HOT brakes and Burning Smells | PriusChat
You can overheat the mechanical brakes on any car and all mechanical braking causes wear. Even worse than overheating and warping the mechanical brakes you can boil brake fluid (especially if the fluid has moisture in it i.e. Black in color) this results in a complete loss of mechanical brakes because now you have a gas in the system instead fluid. I have seen boiled brake fluid cause an accident and our own Toyota Avalon has had several disk warped by family members that don't downshift coming down the mountains. Drivers of commercial vehicles are taught that they must downshift to avoid overheating their brakes, owners of passenger vehicles can get away with not downshifting most of the time though warped brakes often result. In any vehicle on a long steep downgrades you should always downshift, transmissions are made to handle it. B mode saves your brakes and charges the battery, why wouldn't anyone use it. I think this a failure of drivers-Ed made worse by the advent of the automatic transmission.
Given that I (nor anyone I have ever driven with) have never suffered warped brakes or brake failures in the environments I drive (which, as I stated above, are as harsh as pretty much anyone is likely to face), I'm curious how people are causing these failures... Do they just lightly ride the brakes the whole way down? Do they insist on maintaining a certain speed and not allowing fluctuation? I don't get it.
Agree with most everything you're saying, except: B mode reduces charging, comparing to D mode. This is by design; the intention being to substitute engine breaking for regen, delaying the battery becoming fully charged. Specifically useful on protracted steep downgrades.
