lol...some of the responses here....anyway, downshifting to a lower gear on a downhill is actually advised over using your brakes, especially in the mountains, as prolonged brake usage on steep downhills will actually heat up your brakes and affect their performance the longer you drive down that hill....Won't hurt the tranny....

I'd never use an auto or manual to downshift and slow down. I might if I want to keep the revs up for the next turn but other than that, I use the brakes. Brake pads are alot cheape than clutches and auto tranny rebuilds.

Especially the auto. IMHO you stress the clutches inside the auto on a hard downshift just as you would during a hard upshift. Heating up the auto clutches/bands and stressing the fluid is a big no no.

downshifting & shifting in general is not going to hurt anything. the tranny computer will protect from a downshift that is too violent. if a downshift would push the engine past redline then it will override the request & the downshift will not happen, for example you can't downshift to 1st at 50mph, & there is no drawback, downshifting is no worse or more ware than accelerating hard... sure, baby it, it'll last longer :)

downshifting will help avoid brake fade, & downshifting does not cause more fuel consumption, the engine is not racing because it's burning fuel... downshifting can actually help improve mpg, as if your at the right rpm, reaccelerating will only take a slight amount of throttle, where if your in too high a gear, you will have to mash the throttle more & the engine will lug to accelerate, fighting a higher gear. this is a very high fuel consumption condition, & can be avoided with a downshift.

being afraid to downshift is like being afraid to leave it in drive while stopped at a light... some think they need to put it in neutral, just as some think it's bad to downshift:)

The TCU will prevent a catastrophic mistake from happening but just because it won't allow a type of shift, doesn't mean it's not stressing the tranny.

no more stress than flooring it on acceleration... less in most cases

Not arguing that point. Point being, hard upshifts are hard on the tranny. Why double the wear just to slow down?

There is a combination of two things in an upshift that you want to look at for wear - (1) high component speed differential and (2) high torque input. In a downshift, you might get (1) but you won't get (2). Negative torque resulting from coasting is about 10% or less drive torque.

Many newer vehicles from the Honda Civic to the G35 use "hill decent control" to shift to a lower gear when you brake downhill thus saving your brakes. (Personally, I find it irritating).

Regarding fuel economy, it is usually mapped on the basis of rpm and throttle position. As stated above, high rpm and no throttle consumes little fuel.

Here's another question -- does not stopping fully when going from reverse to drive and vice-versa affect ATs?

I'm not an expert, but I would think YES. I always make sure I'm fully stopped to do so...only takes an extra 1 second to do so anyways.

Is the torque applied from the motor during an upshift diff than the torque applied by the wheels when downshifting into a lower gear?

Hill decent? I've not noticed any down shifting of my auto during any a descent of any kind.

The only automobile that I've read that has this is something like a Range Rover where it assists the user when creeping down very steep declines

Under the assumption that we are slowing down, yes the torque is different. Coast torque is assigned as negative in the design process and typically quite small. It is interesting that coasting also creates a completely different load scheme in the transmission.

The '07s do it. It pissed me off to no end in my recent loaner. Living in Pittsburgh we have lots of hills and it was always engaging.

Yeah I do too, but it seems most people don't. I don't get it.

Let's say you are going down a big, steep hill. Then let's assume you downshift from 3rd to 2nd right at the limit of the shift parameters.

Are you saying that the force applied to the at's clutches/bands to slow the car down is significantly less than the force required to shift the gear up on a hard shift?

Well that's sort of the exception vs the rule IMHO. As all the G/Zs built from 03-06 do not have this feature and therefore will probably experience higher wear from attempting this.