Gareth wrote:Are you sure about this? Generally, light throttle will allow the gearbox to change up to the highest possible gear, possibly to reduce frictional losses by making the engine turn slower. In turn this means there is precious little engine braking, which would feel very similar to disengaging the clutch in a car with a manual gearbox. If the clutch is disengaged, fuel is used to keep it turning, whereas a minimal amount of fuel is used if the engine is just providing enough power to maintain the current speed with hardly any load, none at all if on the overrun.
Porsche call it gliding, Mercedes call it sailing (and there is a pretty little picture of a sailing boat in the dash while you are 'sailing'). When coasting with your foot off the throttle before implementation of this function there was an over-run fuel cut-off, meaning that no fuel was used but there was a little engine braking. Now they have decided that economy is optimised by disconnecting the drive so that there is no engine braking at all, although this means that a little fuel is used to keep the engine idling (I have not yet experienced the stop/start while coasting feature described in the article about the new A8). In my wife's Merc this feature only operates in Eco mode, in my son's it also operates in Comfort. In Porsches, the function is disabled if you disable stop/start. I have not found it weird to drive with - a typical unobservant driver would not notice it, I have tried to take advantage by lifting off earlier than I otherwise would in order to maximise the economy benefit of the free-wheeling coast. I have never experienced the difficulty of driving downhill which Insanity describes - but if the car started to speed up more than I wanted it to I would generally select a lower gear manually.
Insanity - in most normal driving good modern autoboxes make a great job of it if left in D, and most auto drivers leave their cars in D all the time. I think most normal drivers also prefer driving with an auto, and there would be even more of them if manufacturers did not charge extra for them. We who practise driving as well as we can as a virtuoso skill believe that there are situations where we can make better gear selections than the autobox - see earlier in the thread for examples. And - this being an advanced driving forum - it is relevant that most examiners enjoy seeing candidates make appropriate use of manual features of an autobox (although you could leave it in D and still get a First).