ACC downhill
 

on my Q7 when i set the speed to say 80km/h..... when i am going downhill...in other cars, the car would normally speed up to faster than 80km/h..... but the Q7 stays on 80..... no matter how steep tbe descent. so my question is..... what is the car using to slow down? brakes or engine?

It uses the gearbox to downshift, which you may be able to pickup on, and brakes.

In all of my recent cars, they will maintain the speed on a downhill also.

Cars use both downshifts and brakes

Which BTW causes what some call 'premature' break wear. Since not a lot of people are aware of how the car can use 'electric' brakes and it's advantages, AND they are used to the old ways, they are surprised that the brakes wore out so quickly - that never happened on my Model A ....

Okay so you are saying then that ACC is bad for brakes ?

Not necessarily, but if you use the ACC a lot and have the distance between cars set to a minimum, the brakes will certainly get more use. Just like when driving without ACC...if you are an aggressive drive always tailing people, you'll use your brakes more

It's even more than that. Remember, every modern assist system is using your brakes, that includes line keep assist, cross wind assist, stability control, etc.

I think also, that ACC is better for driving down steep hill rather than without it.
With my previous car (my wife is using it now), Audi A6 (C7) I changed front brake pads for the first time at 100'000km. And rear brake pads at 120'000 km (car is already 6years old). And I think they could go another couple thousand km, but front was changed along with front wheel bearing, rear in last 120'000 km service last week. Besides, change of front wheel bearing is the only repair job done on my Audi A6 at 120'000 km. Very, very reliable car.
Will see, how Q7 will keep it's reliability record. Now for 27'700 km excellent record.

The etron has a cool feature, it uses the nav to slow in turns or tight corners and uses the regenrative braking to slow the car down, it serms. However, my car accelerates 1-2 kmh downhill in contrast with op observations.

To your point, I commute on the highways in the Philadelphia area everyday, stop and go all the way. I love the ACC and use it daily, but just had my 10000 mile check and sure enough, my front brake pads were in the "yellow" range, less than 9mm remaining. Guess I better get ready for new brake pads in another 10000.