Hypothetical: Would cutting the brakes make the car unstoppable?

[MBCook]

So today I saw a show use that old plot device of cutting someone’s brake lines so they’d get in an “accident”, and that got me thinking. Every guide to servicing brakes I’ve ever seen also makes a big point about not getting grease on the breaking surface for similar reasons

I know regen can slow the car almost to a complete stop, but if you do it slowly enough can it go to zero? Or do the friction brakes always kick in right at the end?

I assume they’re used to hold the car when you’re at a stoplight or whatever, but will ignore that for this question.

What about slamming on the brakes? I know that uses the friction brakes to be able to stop as fast as possible. But does it also use the motors? So with dead friction brakes could you still stop by slamming the pedal, it would just take a much longer distance?

So if something suddenly happened while you were driving causing the friction brakes to be unable to function, just how would the car behave?

For obvious reasons I have no interest in testing this myself.

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[DugthePug Dad]

I would use the parking brake

 

[MBCook]

Sure in an actual emergency I would reach for the emergency brake/parking brake. What I’m curious about is what would happen without it.

 

[Mach-Lee]

So today I saw a show use that old plot device of cutting someone’s brake lines so they’d get in an “accident”, and that got me thinking. Every guide to servicing brakes I’ve ever seen also makes a big point about not getting grease on the breaking surface for similar reasons

I know regen can slow the car almost to a complete stop, but if you do it slowly enough can it go to zero? Or do the friction brakes always kick in right at the end?

I assume they’re used to hold the car when you’re at a stoplight or whatever, but will ignore that for this question.

What about slamming on the brakes? I know that uses the friction brakes to be able to stop as fast as possible. But does it also use the motors? So with dead friction brakes could you still stop by slamming the pedal, it would just take a much longer distance?

So if something suddenly happened while you were driving causing the friction brakes to be unable to function, just how would the car behave?

For obvious reasons I have no interest in testing this myself.

If the hydraulic lines are cut, the car can still slow to a stop with the motors, and then it will engage the parking brake, park pawl, and set a bunch of warnings.

In reality, you’ll probably get a warning of a brake system fault as soon as you start the car. The car will notice the loss of pressure and response in the brakes during the initialization procedure at key on. The braking system on this car is significantly smarter and it has greater fault monitoring since it uses brake-by-wire.

 

[MBCook]

It hadn’t occurred to me it might engage the parking brake automatically when you stop. But given it can tell the brake system failed that really makes a lot of sense.

Thanks!

 

[Star Lord]

I thought I read somewhere if the breaking system detects a fault it won't even let the car move.

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