Adaptive Cruise Control

Cestrian · Feb 3, 2019

I was behind a VW recently on a dual carriageway and the brake lights kept coming on. I wondered why he would use the brakes unnecessarily and it occurred to me that maybe he was using ACC. Which begs the question, do the brake lights keep coming on when a car overtakes and pulls in front of you or does the engine slow you down - or both?

IWMTom · Feb 3, 2019

Cestrian said:
I was behind a VW recently on a dual carriageway and the brake lights kept coming on. I wondered why he would use the brakes unnecessarily and it occurred to me that maybe he was using ACC. Which begs the question, do the brake lights keep coming on when a car overtakes and pulls in front of you or does the engine slow you down - or both?

Yep, if someone comes infront of you it'll use the brakes to increase the distance.

IanLS16 · Feb 4, 2019

If someone cuts in front of you where you'd ordinarily need to brake can understand it doing that, however if you cruise up to a point where you have a car in front of you (ie I'm doing 70mph and car in front is 65mph does it still use the brakes or just cut the acceleration?

IWMTom · Feb 4, 2019

IanLS16 said:
If someone cuts in front of you where you'd ordinarily need to brake can understand it doing that, however if you cruise up to a point where you have a car in front of you (ie I'm doing 70mph and car in front is 65mph does it still use the brakes or just cut the acceleration?

Depends how fast the computer reacts. It'll try and gradually slow you down but it may need to intervene with the brakes. It's not fantastic, but it sort of works.

asif · Mar 26, 2019

It would definitely use the brakes and also make the brake lights come on so that the person driving behind knows your car is slowing down for them to slow down also.

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Andy_L · Mar 27, 2019

Ah well thats that one answered, I've often wondered whether the brake lights come on with slight speed corrections, I use ACC often. So, as impressed as I am whilst driving at how the ACC keeps me and the car in front apart at a set distance, there's a driver behind me thinking wtf is this brake stabber all about

From a personal point of view I'd prefer the brake lights not to come on when the ACC is making subtle corrections, some tolerance built in so not to annoy the car following, with the brake lights coming on only when really needed.

Finglonga · Mar 27, 2019

The brake lights rarely come on on mine unless the car slows quickly like with normal driving. More likely just someone riding the brakes as they are bad at driving, the VW system doesn't drive like that to need to activate the brakes repeatedly.

dr_mat · Mar 27, 2019

If you are approaching a slower car from a way away and it has time it will simply lift off the throttle to slow you down progressively, but yes if it needs to lose speed more quickly then it'll use the brakes.

bertj · Mar 27, 2019

ACC uses the brakes to slow the car going down a hill; it seems to be very effective. However ordinary CC on my wife's DSG Fabia doesn't seem to use the brakes when going down a hill so the car can exceed the set limit; somewhat disconcerting if the CC is set at the speed limit. I don't know if this is also true of Golfs etc. with ordinary CC.

ColinStone · Mar 28, 2019

Ordinary CC doesn't use brakes - just lifts off throttle. On steep hill car will keep accelerating and use the kinetic energy gained to coast further on the run out at the bottom - brilliant!!

bertj · Mar 28, 2019

ColinStone said:
Ordinary CC doesn't use brakes - just lifts off throttle. On steep hill car will keep accelerating and use the kinetic energy gained to coast further on the run out at the bottom - brilliant!!

Yes, you can rely on ACC to prevent you exceeding the speed limit whatever the gradient but definitely not with standard CC.

Cestrian · Mar 28, 2019

This from the VW website confirms:
'If approaching a slower vehicle ahead or if another vehicle cuts in front of you, the adaptive cruise control slows down the car by initiating corrective controls in the engine management and, if necessary, in the braking system too. If the required rate of deceleration exceeds 30% of the vehicle's maximum stopping power, visual and audible warning signals will prompt the driver to apply the brakes manually.'

cambs_gti · Jun 20, 2019

Cestrian said:
This from the VW website confirms:
'If approaching a slower vehicle ahead or if another vehicle cuts in front of you, the adaptive cruise control slows down the car by initiating corrective controls in the engine management and, if necessary, in the braking system too. If the required rate of deceleration exceeds 30% of the vehicle's maximum stopping power, visual and audible warning signals will prompt the driver to apply the brakes manually.'

This.

REALLY not difficult to find this sort of info online. I knew the 30% figure before I'd even decided I was going to buy the bloody car

Adaptive Cruise Control

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