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Rear collision avoidance systems and the HPDE environment

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Old 03-18-2017, 10:07 AM   #31
needmoregarage
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^ thank you - I thought maybe it was "belts and suspenders " for disabling the system as it's been noted these systems may not be fully disabled even when off.

Now I understand your comment about replacement cost!
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Old 03-18-2017, 06:25 PM   #32
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Originally Posted by needmoregarage View Post
I agree DTMiller - and I think my explanation was inarticulate. If someone cuts in front of someone with the braking system - the car that was cut in front of will brake hard when it senses a car suddenly in front. If anyone is following them and not expecting it (even if they are at a reasonable distance) - toward the end of a straight where speeds are high and lots of ground is covered every second - if the driver in the following car does not expect hard braking ahead, and doesn't react immediately, or has someone on their tail....it could be serious. It could easily become a chain reaction if enough cars are following in close proximity.

Still not sure I'm drawing a "clear" picture (even though I can imagine it in my head I don't know if I'm articulating)
That is unlikely to happen because the brake application is triggered by the relative speed of cars more than the distance. So if the car cutting in front has the same or higher speed, the system will likely not trigger, maybe just do a warning beep. I'm describing this based on my experience with the current gen Cayenne.

Where this system can be dangerous is when a car with such a system is passing and gains passing speed while still behind the car being passed, even if partially (e.g., to use draft or to have a better line). The system does not "know" that the driver is about to turn and pass the obstacle and assumes the obstacle is getting rear-ended. Happened to me once.

Unlike other nannies, this one can actually be very disruptive and dangerous even for a relative beginner. And it only helps if you are not paying attention, which should not happen on a track anyway. So I'd turn it off as a matter of policy.
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Old 03-18-2017, 06:50 PM   #33
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^ My experience is different. Our car allowed you to set the distance, and it would brake as soon as the distance was reached. It was not relative to speed.
In a friend's 2017 VW R32 - his car also allows him to set for distance (near, med and far - not sure what that equates to in car lengths or meters or whatever but he has 3 choices for "sensitivity"). He may also turn it off.

What about this situation: You just came onto the front straight at the GLen (or any long straight). You are overtaking a slower car who sees you coming and gives a point. You pass them and even though you are going faster - when you cut back over in front of that car - his system kicks in and brakes hard, in the middle of a straight when no one would be expecting a car to brake hard. Lets say there's someone behind him. That person is not expecting a car ahead to brake hard until they get close to the turn at the end of the straight.

Now take a group of newbies who often get nervous about being off line and always seem anxious (in my experience) to get back online after passing someone.

I can easily see where proximity to other cars could causes a car to brake hard, and where it could happen in a very surprising way which could result in an accident if everyone around isn't fast with reactions and paying attention. And if attention is drawn for even a moment to something else (lets say they glance in the mirror or at the instruments for a moment) - that's all it takes for a collision.

I agree that the system can be dangerous in the circumstances you describe, but I think it could be more widespread than that. And I am not familiar enough with the various systems in different cars to understand if some might be "better" than others - but it would seem there is no place for this on a race track (either by disallowing the car, or by requiring the driver to disable the system).
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Old 03-18-2017, 07:03 PM   #34
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Originally Posted by needmoregarage View Post
^ My experience is different. Our car allowed you to set the distance, and it would brake as soon as the distance was reached. It was not relative to speed.
In a friend's 2017 VW R32 - his car also allows him to set for distance (near, med and far - not sure what that equates to in car lengths or meters or whatever but he has 3 choices for "sensitivity"). He may also turn it off.

What about this situation: You just came onto the front straight at the GLen (or any long straight). You are overtaking a slower car who sees you coming and gives a point. You pass them and even though you are going faster - when you cut back over in front of that car - his system kicks in and brakes hard, in the middle of a straight when no one would be expecting a car to brake hard. Lets say there's someone behind him. That person is not expecting a car ahead to brake hard until they get close to the turn at the end of the straight.
I verified that Cayenne would not brake in such situations. Would beep a lot at most. Although it could engage brakes as you are preparing to overtake if you are behind the slower car as you approach and not to the side enough. But the fact that different systems behave drastically differently is another reason to keep them off.
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