Go123

Does anyone know if the ACC uses the front and rear brakes equally, or when it chooses which to use?

tenspeed

It is my understanding that the ACC uses the rear brakes.

gk1

It uses all the brakes same as if you stepped on the brake pedal...otherwise it wouldn't be able to bring the car to a complete stop safely.

Go123

That would makes sense, but from my experience it won't use full braking unless it is trying to avoid a collision at the last second. As if it does not have full access to max braking unless a crash is imminent.

gk1

LOL. Well of course it doesn't use full braking all the time...that would indeed be an uncomfortable journey. But it would have no reason to not use all four corners any time it needs to slow down and let the advanced electronics ABS ESP and electronic brake force distribution do it thing as designed.

Go123

By full braking I was implying using front and rear brakes equally not so much max braking force. It seems some think it favors mostly using the rear brakes.

gk1

Ah ok understood. I doubt very much they would have rears favored but best way to find out would be to VCDS log and see braking pressure in each brake channel.

snagitseven

I'm pretty sure ACC uses the rear brakes to maintain set speed and following vehicle distance if required. When activated, Presense front uses both front and rear bakes for emergency stopping.

the_duke

Not sure how you would find a definitive answer but I believe it uses the brakes in the same manner as if you pressed the pedal. If it didn't people would be sliding all over the place in slippery conditions.

tenspeed

There is a warning in the owners manual about using cruise control "in the city, in stop and go traffic, on twisting roads and when road conditions are poor (such as ice, fog, gravel, heavy rain and hydroplaning) - risk of accident."