ACC breaks too strongly

drummerdimitri

drummerdimitri

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I've realized that even though the distance between my car and the one in front of me is relatively large, the car still breaks a little late and hard if the car in front of me comes to a stop abruptly.

I personally don't mind it but I am always afraid of some ******* sticking too close to my *** and rear end me because of this.

What do you guys think?
 
What's your ACC set to in drive select?

On 'Dynamic' it brakes hard and late. On 'Comfort' it's a lot earlier and tends to get off the gas before braking.
 
a3_phil said:
What's your ACC set to in drive select?

On 'Dynamic' it brakes hard and late. On 'Comfort' it's a lot earlier and tends to get off the gas before braking.
Click to expand...

I have it set on comfort. I like the way it accelerates when a car ahead has moved out of my lane but the braking is just too sudden for my taste.

Maybe the ACC sensor is not calculating the distance of the car ahead fast enough. Anyone know if that might be the case and how many times a second it does so?
 
Hmm, difficult to say then as it's all going to be so subjective. I can't say I've ever felt ACC to be late or hard on the brakes on 'Comfort'. If anything I find it a little early to ease off (e.g. on dual carriageways) where I'm not even thinking about pulling out to overtake yet.
 
a3_phil said:
Hmm, difficult to say then as it's all going to be so subjective. I can't say I've ever felt ACC to be late or hard on the brakes on 'Comfort'. If anything I find it a little early to ease off (e.g. on dual carriageways) where I'm not even thinking about pulling out to overtake yet.
Click to expand...

I am sure people in the UK are smoother drivers than the Lebanese ones so that might be why you don't find the braking too sudden.

It works great when the car ahead comes to a stop very gradually but strong braking from the car ahead results in even harder braking from my car since it it too slow to react.

I usually override the system if I feel the car ahead is going to stop abruptly to avoid being rear ended and/or having people question my driving skills.
 
On long runs I have my car in efficiency. In general, the ACC in this mode decelerates in the same manner I would. In other modes it can be a little more harsh.
 
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Will gi
Fox5150 said:
On long runs I have my car in efficiency. In general, the ACC in this mode decelerates in the same manner I would. In other modes it can be a little more harsh.
Click to expand...

Will give it a try thanks!
 
Sometimes my ACC doesn't even cope with braking. It does normally, but occasionally it can't be bothered.

Today was a case in example. On the motorway doing 85, Distance 2, in a stream of traffic, the car in front brakes, my ACC brakes, but not hard enough. Instead it gives me the Pre Sense "Bing" whereby I have to stamp on the brakes myself.

It was set on Dynamic.

Kinda defeats the whole point of ACC if it can't be bothered to brake hard enough for me. It's been in twice to the dealer to get the sensor checked and aligned previously.
 
The one thing I have noticed recently that's annoying me is I'm sure the distances are further back than they were when I first got it. I've got it on distance 1 the majority of the time on the motorway and I don't remember the gap being that big. For reference it's just inside the two chevron distance that some motorways mark as a safe travelling distance. I'd expect that to be maybe setting two or three? I don't want to be travelling closer, but I would have thought that distance 1 would have been.
 
The more I think about ACC, the less I think of it.

Wouldn't you rather overtake a car driving cruise control on the interstate rather than let ACC slow you down to the car driving in front of you?
 
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The other foible that I can re-create with my ACC is this.

Pulling away from a roundabout exit at say 30 mph, I set the ACC to 80. There is a car in the distance, going around say 35 mph.

The ACC (in Dynamic mode) accelerates up to the target speed, but before it reaches the target speed, the car in front comes into range.

The ACC, however, is still accelerating, closing the gap, and instead of backing off or braking, it will issue the Pre-Sense "Bing" - whereby I have to intervene and brake to stop the car colliding.


On the whole it works in "normal" undemanding situations, good in traffic jams in conjunction with DSG, but put it in more complex situations, say accelerate to target speed and encounter a much slower car, it struggles.


Probably, because, the ACC system on the A3 is a very very basic variant - other ACC systems higher up the range (e.g.: A6) use 2 radar sensors and the monochrome camera to evaluate all the information. The A3 version only has 1 radar sensor.
 
Strange v8, I've never had that problem myself and I use it for 90% of my driving. Maybe (yet another!) fault for you?

IIRC ACC can't use more than 30% of maximum braking force so maybe some of these situations require more which is why you're getting the prompt?
 
I think it's Pre-Sense front only uses around 30% of the braking force above 19mph, it would be a bit bad if ACC couldn't use 100% of the braking force !

(eg: In Lane 2 or 3 in a stream of moving traffic doing 70mph, cars in front suddenly brake, the ACC should be able to stop the car!)
 
OK I found this in the manual, which explains what is happening, but not why:

So those 2 situations I described above, it doesn't cope with! Brilliant!


Untitled.jpg
 
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gamegenie said:
The more I think about ACC, the less I think of it.

Wouldn't you rather overtake a car driving cruise control on the interstate rather than let ACC slow you down to the car driving in front of you?
Click to expand...

Very, very good point. In fact that's one of the great things about CC - it's amazing how many drivers slow down at certain points. e.g. on a motorway slight bend everyone seems to slow by 5mph.

Within ACC I probably wouldn't notice how slow I'm going until I realise I'm not overtaking anyone!
 
veeeight said:
OK I found this in the manual, which explains what is happening, but not why:
Click to expand...

I've had that red lamp come on even when ACC is switched completely off to tell me I'm following too closely for it to react if it was on. I have also experienced the "closing the gap too fast" and the stopping too abruptly phenomena. On close distance settings it almost does panic stops if the person in front brakes slightly harder than normal. I find myself adjusting the distance switch as traffic patterns change to keep it in the sweet spot. Drivers around here are not smooth at all.
 
Last edited:
veeeight said:
The other foible that I can re-create with my ACC is this.

Pulling away from a roundabout exit at say 30 mph, I set the ACC to 80. There is a car in the distance, going around say 35 mph.

The ACC (in Dynamic mode) accelerates up to the target speed, but before it reaches the target speed, the car in front comes into range.

The ACC, however, is still accelerating, closing the gap, and instead of backing off or braking, it will issue the Pre-Sense "Bing" - whereby I have to intervene and brake to stop the car colliding.


On the whole it works in "normal" undemanding situations, good in traffic jams in conjunction with DSG, but put it in more complex situations, say accelerate to target speed and encounter a much slower car, it struggles.


Probably, because, the ACC system on the A3 is a very very basic variant - other ACC systems higher up the range (e.g.: A6) use 2 radar sensors and the monochrome camera to evaluate all the information. The A3 version only has 1 radar sensor.
Click to expand...

Yeah, the ACC on the A6 is notably more expensive, it seems to be a more complex system with the extra sensors etc.
 
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