ACC how good is it...

Joetidman

Joetidman

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So can someone tell me, can it cope with 70 - 20 - 70 mph changes which happens quickly, say over 30 seconds or so? On my M25 journeys the speed can change quickly and requires significant braking and acceleration. Can the ACC handle that or is it only for more gentle 70-80-70 changes?
 
the_lecht_rocks said:
yest - it's qte brilliant in operation, as log as you have STronic.
Click to expand...

ACC is brilliant in manuals too, do not think anything else. ACC together with a few other things including B&O and the comfortable sport-suspension (feels like the standard would be far to soft) are very positive surprises in the 8V.
 
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I also found it great , drove down to Italy last month most of the way on ACC a very relaxing way to drive, one niggle is that if you don't get the distance right when overtaking a wagon it slows you down just as you pull out into the outside lane, also quite impressed how it "learns" that youre not undertaking a car when on foreign roads - I wouldn't be without it.
 
There is an option on the drive select to adjust the acc for either dynamic or comfort. Not really tested but I think this adjusts how quickly it gets you up to target speed. I've also noticed that in efficiency mode it's very slow to accelerate with acc
 
That's amazing then, makes me look forward to it even more. Of course in rush hour M25 traffic there is only one setting allowed, ultra-dynamic, I.e. Leave half a car space regardless of speed, so I will just set it to that ;)
 
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While I've stated many times that I think ACC is great, and use it almost all the time, I do have to spread a note of caution. The OP asked specifically about 70-20-70 speed changes and this is one area that the driver needs to be aware of and be ready to act as soon as he/she believes the ACC is in danger of failing to slow down in time. The reason for this is simple: the ACC attempts to keep a certain time interval (by default around 2 seconds at distance 3 setting) behind the car in front. If the car in front slows down, even fairly rapidly, from 70 MPH to 20, the ACC will generally be ok on its own. If however, you're travelling at 70 MPH with no car directly in front, but you then come up to a line of traffic doing 20 MPH you will have to brake yourself. 2 seconds is simply not enough time for the ACC to detect the almost stationary traffic and slow down. This is where the human brain and eyesight is much better at judging hazardous situations than the processor and sensor(s) of the ACC.
 
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constvoid said:
While I've stated many times that I think ACC is great, and use it almost all the time, I do have to spread a note of caution. The OP asked specifically about 70-20-70 speed changes and this is one area that the driver needs to be aware of and be ready to act as soon as he/she believes the ACC is in danger of failing to slow down in time. The reason for this is simple: the ACC attempts to keep a certain time interval (by default around 2 seconds at distance 3 setting) behind the car in front. If the car in front slows down, even fairly rapidly, from 70 MPH to 20, the ACC will generally be ok on its own. If however, you're travelling at 70 MPH with no car directly in front, but you then come up to a line of traffic doing 20 MPH you will have to brake yourself. 2 seconds is simply not enough time for the ACC to detect the almost stationary traffic and slow down. This is where the human brain and eyesight is much better at judging hazardous situations than the processor and sensor(s) of the ACC.
Click to expand...

Ah that is very useful information thanks, I always expected to keep constant vigilance but good to know to cover the brake approaching stationary traffic when nothing is locked on, ta
 
constvoid said:
While I've stated many times that I think ACC is great, and use it almost all the time, I do have to spread a note of caution. The OP asked specifically about 70-20-70 speed changes and this is one area that the driver needs to be aware of and be ready to act as soon as he/she believes the ACC is in danger of failing to slow down in time. The reason for this is simple: the ACC attempts to keep a certain time interval (by default around 2 seconds at distance 3 setting) behind the car in front. If the car in front slows down, even fairly rapidly, from 70 MPH to 20, the ACC will generally be ok on its own. If however, you're travelling at 70 MPH with no car directly in front, but you then come up to a line of traffic doing 20 MPH you will have to brake yourself. 2 seconds is simply not enough time for the ACC to detect the almost stationary traffic and slow down. This is where the human brain and eyesight is much better at judging hazardous situations than the processor and sensor(s) of the ACC.
Click to expand...

Thats fine and likely correct. What if you actually would do nothing in the above scenario, approaching the slow moving line of cars - the ACC would put the car a kind of a state of emergency mode and start to brake as in a panic mode trying to avoid a crash? But without guaranties it would be able to avoid impact?
 
Just asked my wife about her ACC and she said, "you have to be careful."

I have only driven with it once. It worked fine when another car was detected and the ACC light showed 2 cars. However, around a tight corner it lost the other car and started accelerating. So had to brake to stop driving into the car.

I think it would work fine 70-20-70 as long as the ACC had detected another car and was showing 2 car icons in the dash. If it was only showing 1 car icon and you were approaching slow traffic, then as my wife says - be careful.

... does that make sense? Be careful around corners and approaching slow moving traffic.

Also, in a queue of traffic, I didn't find it was braking very smoothly and I had set it from standard to comfort and distance to max/5. Are there better settings for traffic queues?

As has been covered extensively in other threads, if the ACC system is following another car and that car takes a slip road, it will cause the car to brake sharply. I do wonder if this could cause an accident.
 
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GreatBallsofFire said:
Thats fine and likely correct. What if you actually would do nothing in the above scenario, approaching the slow moving line of cars - the ACC would put the car a kind of a state of emergency mode and start to brake as in a panic mode trying to avoid a crash? But without guaranties it would be able to avoid impact?
Click to expand...

You'd get the audible alarm and displays on the DIS to show you're too close. At lower speed differentials when that has happened to me I've never given it chance to prove its capabilities - I've hit the brakes myself just to be sure. I think at the 70-20 differential there wouldn't be enough time for the ACC or the driver to slow the car down safely. Remember that Pre-Sense Front (which is what would initiate the emergency braking), is only stated to operate below a certain speed, which off hand I can't remember. I think it would begin to act, but wouldn't slow down enough.
 
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I find motorway driving so boring. I like the fact I have to drive cause it takes my mind off it and keeps me awake. Not sure how I'd be if all I had to do was steer the car
 
constvoid said:
Remember that Pre-Sense Front (which is what would initiate the emergency braking), is only stated to operate below a certain speed, which off hand I can't remember. I think it would begin to act, but wouldn't slow down enough.
Click to expand...

Pre sense front works at all speeds - regardless of whether ACC is on or off. And assuming you've switched it on in the MMI.

It's just the complete autonomous braking to a complete stop that works only under 19 mph.

At all other speeds, it will give you the BEEP, Visual Warning, and Braking JOLT, then only apply partial (up to 30%) braking pressure.

Then when you wake up and press the brake pedal, it will add the remaining brake pressure required to stop you before you hit the car in front, but allowing for max distance for the following car.

edit: This is quite a good explanation:

cartechnical | Audi safety track test - YouTube


 
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GreatBallsofFire said:
ACC is brilliant in manuals too, do not think anything else. ACC together with a few other things including B&O and the comfortable sport-suspension (feels like the standard would be far to soft) are very positive surprises in the 8V.
Click to expand...

I would have though ACC is a manual is an odd thing - surely you would stall the car
 
It is not possible to have Stop/Go ACC down to zero mph in a manual, no.

Manual Gearbox - ACC only between 19 and 93 mph
S-tronic - ACC between 0 and 93 mph

In both cases this is increased to 124mph with the driver assistance package (has the camera and upgraded radar sensor)
 
royalsteve68 said:
I would have though ACC is a manual is an odd thing - surely you would stall the car
Click to expand...

I think the following other traffic in a traffic queue on works with s-tronic but all the other 'parts' of ACC work with s-tronic and manual.

Pages 120 and 121 in the Owner's Manual cover the various ways ACC works with Vehicles with a manual gearbox and Vehicles with an automatic gearbox. With a manual ACC only available in second or higher gear.
 
veeeight said:
Pre sense front works at all speeds - regardless of whether ACC is on or off. And assuming you've switched it on in the MMI.

It's just the complete autonomous braking to a complete stop that works only under 19 mph.

At all other speeds, it will give you the BEEP, Visual Warning, and Braking JOLT, then only apply partial (up to 30%) braking pressure.

Then when you wake up and press the brake pedal, it will add the remaining brake pressure required to stop you before you hit the car in front, but allowing for max distance for the following car.

edit: This is quite a good explanation:

cartechnical | Audi safety track test - YouTube


Click to expand...


You're right about pre-sense working at all speeds of course - I was referring to it braking to a halt without the driver doing anything. I'm still not sure it would cope with the 70-20 situation above though, even with the driver tapping the brake to confirm braking is allowed, as there are still limitations on the % brake force it uses. I doubt I'll ever find out though, as I would take over control myself.
 
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h5djr said:
I think the following other traffic in a traffic queue on works with s-tronic but all the other 'parts' of ACC work with s-tronic and manual.

Pages 120 and 121 in the Owner's Manual cover the various ways ACC works with Vehicles with a manual gearbox and Vehicles with an automatic gearbox. With a manual ACC only available in second or higher gear.
Click to expand...

You are correct as usual, I had the possibility to test the system both yesterday and today, and it is, as already said, brilliant also in manual car. When I did encounter a sudden traffic stop following a bend the ACC instantly (before had the time to react) started to brake. In case you need to change gear, it will tell you to do so. But having a diesel and e.g. driving on the motorway that is most times not needed. Again, really handy and convenient system when you just want to cruise effortless. The 8V is indeed refined and mature compared to the 8P. Less "brutal" as well of course, but I don't I think I will miss that too much.
 
Yesterday I was driving along a B road in a 40mph zone with ACC on. The road was a typical B road, very quiet with a white centre line and a good width. As I approached a cyclist going the same way as me with the aim of overtaking him a car came round the bend in the opposite direction. There was loads of room to drive a coach through and it wasn't necessary for me to cross the white line but the ACC rammed the brakes on. Happily, the Alfa 146 behind me was far enough away to slow without incident. ACC is very useful in speed limited zones but you have to accept it can have its drawbacks. With the original non-adaptive cruise on my previous 8p I would have sailed past the cyclist without incident.
 
^ it may have been Pre Sense Front, rather than ACC that applied the brakes.

You can turn off Pre Sense Front in the MMI.
 
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Pre-sense was on. It no longer is. I'm renaming it 'Collision Assistance' and keeping it off.
Page 126 of the handbook - 'Due to inherent system limitations, false activation of the system is possible'
Page 127 - Please note that pre-sense front can apply the brakes unexpectedly.'
I had a momentary feeling of helplessness yesterday and won't be encouraging any more of that.
 
Take Care - Although it could have been pre-sense, it could still be the native ACC - although you say the road was wide, you also say it wasn't necessary to cross the white line to overtake. In that situation ACC would be tracking the bike and would therefore attempt to match speed. The ACC will err on the side of caution. In fact it would have been apparent if it were pre-sense, as the alert tone would sound, and the DIS would show you were too close. I personally would never switch pre-sense off, as it does give you that extra warning if the ACC is in danger of being unable to cope with the situation.

In similar situations, all you need to do is apply a minimal amount of throttle - this will override the ACC and allow you to carry on without unnecessary brake application.
 
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constvoid said:
Take Care - Although it could have been pre-sense, it could still be the native ACC - although you say the road was wide, you also say it wasn't necessary to cross the white line to overtake. In that situation ACC would be tracking the bike and would therefore attempt to match speed. The ACC will err on the side of caution.

In similar situations, all you need to do is apply a minimal amount of throttle - this will override the ACC and allow you to carry on without unnecessary brake application.
Click to expand...

It's like a lot of things on new cars. You have to learn to adapt and drive accordingly. The first vehicle I drove was a Honda 50cc moped with an automatic clutch. When I learned to drive a car I had to adapt and learn how to use a clutch properly. I drove with a clutch for many years and then decided to have an s-tronic and had to adapt my driving to suit. No doubt when I get my new 8V I will have to adapt to many other new things - electronic handbrake, hold assist, ACC, more steering wheel buttons etc but surely that adds to the fun of driving and stops it becoming boring.
 
Thanks constvoid. I'm pretty certain it was the pre-sense as I was virtually abreast of the cyclist when the car stood on its nose.
 
Well, h5, you're more than welcome to my bit of driving fun yesterday.
 
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