Dumb question re ACC

Technical Forum for the Porsche Macan
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Nuclear Nick
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Post by Nuclear Nick »

On-Track wrote: Tue Dec 21, 2021 1:12 pm
Paul1970 wrote: Tue Dec 21, 2021 9:49 am Have just started experimenting with ACC and wondering if anyone knows:

1. When it slows you down does it use the brakes because it feels like the slowdown comes from the engine reducing power, and
2. Do the brake lights come on?

The reason I ask is that I was on the motorway and there was a lorry behind me when someone pulled across in front of me and my car slowed down rapidly via the ACC. I was wondering whether the lorry behind got a warning via my brakes.
It will also use the brakes on downhill gradients to stop the car exceeding the selected speed. This is a step forward from the standard cruise control which just "pings" if you go over the set speed.
I had standard cruise control on the Macan and same on the 911. It does use the brakes to slow the car on downhill sections to avoid exceeding the set speed.
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mueslibrown
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Post by mueslibrown »

I had a scare on Saturday - all of a sudden the car braked sharply, warning sound beeping and 'collision detection' appeared on the digital dial. Looked around and could see or feel nothing that could have 'hit'. It came completely out of the blue ... I was very spooked.
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Post by PorscheMack »

The more I hear about ACC, the less I want it.. 🤔
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Post by On-Track »

Nuclear Nick wrote: Tue Dec 21, 2021 5:16 pm
On-Track wrote: Tue Dec 21, 2021 1:12 pm
Paul1970 wrote: Tue Dec 21, 2021 9:49 am Have just started experimenting with ACC and wondering if anyone knows:

1. When it slows you down does it use the brakes because it feels like the slowdown comes from the engine reducing power, and
2. Do the brake lights come on?

The reason I ask is that I was on the motorway and there was a lorry behind me when someone pulled across in front of me and my car slowed down rapidly via the ACC. I was wondering whether the lorry behind got a warning via my brakes.
It will also use the brakes on downhill gradients to stop the car exceeding the selected speed. This is a step forward from the standard cruise control which just "pings" if you go over the set speed.
I had standard cruise control on the Macan and same on the 911. It does use the brakes to slow the car on downhill sections to avoid exceeding the set speed.
All I can say Nick is it didn't on my 2015 Macan SD or on my 2013 Cayenne. It was one area where I thought Porsche were inferior to Mercedes which did use the brakes to control speed. Maybe it was corrected in later years.
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Post by AllanG »

PorscheMack wrote: Tue Dec 21, 2021 6:03 pm The more I hear about ACC, the less I want it.. 🤔
Me too...I’d rather be in control!
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Post by Paul1970 »

PorscheMack wrote: Tue Dec 21, 2021 4:09 pm
Paul1970 wrote: Tue Dec 21, 2021 4:01 pm
Neil1911 wrote: Tue Dec 21, 2021 3:13 pm ^^^ the above two and its strict adherence to the set space in front leads it to use the brakes far more than you would yourself and reduces their longevity. Had to have my rear pads replaced after 20k so I have modified how I use the ACC and take over myself if it looks to be lots of speed varation required, reverting to ACC when a greater cruise element returns, be that at 10 or 77 mph.
After dipping my toes into the ACC world today I came to exactly the same conclusion in terms of using only when road conditions dictate that it should remain relatively steady driving. It's a bit nerve racking on a busy motorway when I would have eased off the gas in anticipation of someone pulling in front of me which would involve no use of brakes but the car had to quite forcefully drop from 75ish to 50 before then accelerating back up to speed because it couldn't anticipate the same as I can due to its "tunnel vision". Given the move towards self-driving I presume that the Tesla, for example, has a more intelligent ACC system because instead of relaxing the driving experience I was more on edge.

And also worth noting that the Lane Keep Assist wanted me to drive in the middle of a country road because it couldn't detect that there were 2 lanes rather than one. "Drive in the centre of the road" it kept warning me :o

Really enjoying getting to know the "safety systems"!
Based on your thoughts would you spec it again?
So I specced ACC with Lane Keep Assist and Speed Limit Indicator. It also seems to recognise certain traffic signs because I noticed it displaying a sharp right bend today.
Based on very limited experience I don't think I'm going to get much use out of ACC. Lane Keep Assist is useful but because so many of our roads have no or faded lines it gets confused. I would definitely want the Speed Limit Indicator though. The reason i went for ACC is because my business partner swears by it, and a number of members on here are big fans also. I think, as mentioned in another post, if you use it in the right conditions it might be a nice option, but if I didn't have it I don't think I'd miss it at all.*

*Caveat: I'm only a few weeks into ownership so reserve the right to change my opinion!
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Post by MacanSman »

mueslibrown wrote: Tue Dec 21, 2021 5:38 pm I had a scare on Saturday - all of a sudden the car braked sharply, warning sound beeping and 'collision detection' appeared on the digital dial. Looked around and could see or feel nothing that could have 'hit'. It came completely out of the blue ... I was very spooked.
Same happened to me yesterday!
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Post by Col Lamb »

Neil1911 wrote: Tue Dec 21, 2021 3:20 pm
Col Lamb wrote: Tue Dec 21, 2021 3:08 pm With ACC turned on but not set (greyed out) the automatic emergency braking system is active.
Col, have you actually experienced this working? Whenever, I've had it that way there's never been a hint of it doing anything, I'm not timid but my nerve always gives way before there's any sign of braking! In the manual I've only seen reference to the car adding brake pressure when the driver is already braking hard and a potential collision is detected. I've been considering a test with a cardboard box but not tried it yet :)
Yes

Set ACC at 30 and the car in front slowed to about 5 mph to turn right, ACC slowed the car to maintain the distance. On another occasion in traffic I let the car brake by itself to a standstill when traffic lights changed, took a bit if nerve to allow it to fully control braking.

Also with ACC set but greyed out in a residential 20mph area I had a driver fail to stop when they came out of a blind junction where they should have given way and they stopped halfway across the road, the ACC initiated an emergency stop. I did not even have time to apply the brakes myself.

ACC does have a flaw, on roads with a lot of heavy spray it can false activate.
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Post by Tracky »

mueslibrown wrote: Tue Dec 21, 2021 5:38 pm I had a scare on Saturday - all of a sudden the car braked sharply, warning sound beeping and 'collision detection' appeared on the digital dial. Looked around and could see or feel nothing that could have 'hit'. It came completely out of the blue ... I was very spooked.
There has been more than one story where a car has emergency braked on its own for no reason and been rear ended !

Hence my comments that I’d rather not have it too as I learnt to drive and read the road not rely on electronics
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Post by Neil1911 »

Col Lamb wrote: Tue Dec 21, 2021 10:31 pm
Neil1911 wrote: Tue Dec 21, 2021 3:20 pm
Col Lamb wrote: Tue Dec 21, 2021 3:08 pm With ACC turned on but not set (greyed out) the automatic emergency braking system is active.
Col, have you actually experienced this working?
Yes

Set ACC at 30 and the car in front slowed to about 5 mph to turn right, ACC slowed the car to maintain the distance. On another occasion in traffic I let the car brake by itself to a standstill when traffic lights changed, took a bit if nerve to allow it to fully control braking.

Also with ACC set but greyed out in a residential 20mph area I had a driver fail to stop when they came out of a blind junction where they should have given way and they stopped halfway across the road, the ACC initiated an emergency stop. I did not even have time to apply the brakes myself.

ACC does have a flaw, on roads with a lot of heavy spray it can false activate.
1. Yes, got that t-shirt, probably what wore out my rear pads;
2. Very interesting, I've approached stationary traffic in that "condition" but had to brake myself, maybe just too timid!
3. Scary, not had that, although it abdicated all responsibility last Friday evening in the heavy mist!
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