Comment by bombcar | Hacker News Reader

Comment by bombcar | Hacker News Reader

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Yeah, any design is going to be various trade-offs, and you have to understand them (and how they may relate to your mission) when determining what to do and what would be a bad decision.

For example, cars have "fail open" brakes but have independent cylinders so that it is relatively hard to have all four wheels fail at the same time (older cars had single master cylinders) - and one of the tradeoffs is that people want cars to get going immediately and not wait for brake cylinders to "charge up".

As more and more things get computerized, you have more options for "intelligent failover" - anyone who used to drive an old manual car knew you could slow down using the engine - but now the computer could detect brake failure and do things for you to help recover.

And as seen from other comments, the modern US military prioritizes "on-road safety" over "under ongoing attack ability" - partially because of changing strategies I suspect, but also from the realization that the US military kills more members of the US military each year via accidents, etc, than anything else.

Pretty much every car made since the 1980s has had dual-circuit brakes with usually one front and one rear wheel cylinder on each circuit. Volvo being Volvo took it further with their 2-series cars in the 1970s and 1980s, where the front discs had four-pot calipers configured as two sets of two-pot calipers. Each braking circuit had one half of each front caliper and one rear caliper, so in the event of one half of the brakes failing it would still stop in a straight line.

You can use engine braking in automatic vehicles too, by simply changing to a lower gear.

Yeah - but as we saw with the floormat/unintended acceleration, many people don't think of it in an emergency (all the fatalities could have been avoided by shifting into neutral in those cases, might have blown up the engine but wouldn't have crashed/killed).

It's something you're taught to do as part of your driving test, or at least you were when I sat mine.

There is one subtle difference between automatic transmissions and manual ones and that is the manual one will allow a shift into a lower gear even when engine damage is likely.

An automatic one will not, and will hold the current gear until car speed falls within shifting range.

Ask me how I know :)

Yeah, newer ones can be too smart for your own good (but not theirs) - older ones had no problem with you slamming it into reverse or park at freeway speeds - ask me how I know!

Ahhh, the classic money shift.

I am reminded of a friend who changed his steering wheel plastic trim, in the process he bumped the wheel position sensor out of calibration. No worries, trigger a recalibration. Uh oh, won't recalibrate.

This of course meant the entire cars safety and stability control systems, ABS and traction control were all disabled. It drove like a tank.

The fix, obviously, was to replace the brake booster primer pump (hybrid car). It had worn enough to no longer recalibrate. Still perfectly functional, and would have kept working for a long time, bit it wouldn't quite meet the factory expected parameters so it failed it's test.

According to the other guy that founded the Range Rover forum I run, in the 1990s when they were getting P38s as traffic cars the training for "really really stop right now" was to throw it into reverse at 70mph and plant the throttle.

It appears that ZF 4HP20/4HP22 gearboxes can do this an unlimited number of times without apparently being damaged, but I'm not trying it on either of mine.

I have always wanted to try that! I'm not going to try it on any car I own either. It is all just super high risk, and I just don't have a spare car laying around that has the beans to pull that off.

Depends on the gearbox. Really modern ones won't, anything more than about ten years old will downshift if you select a lower gear.

Well, I have a 2000 Honda that won't do it. And I had an 03 Kia that also won't do it.

> For example, cars have "fail open" brakes but have independent cylinders so that it is relatively hard to have all four wheels fail at the same time (older cars had single master cylinders) - and one of the tradeoffs is that people want cars to get going immediately and not wait for brake cylinders to "charge up".

And emergency brake that's wholly separate circuit.

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