You will use a little bit more gas, because the engine revs higher on a downshift, although with the throttle totally closed I believe the injectors will be totally off so maybe you won't use any more after all.
It's not "bad", but you should throttle-match the downshifts ("blip" the throttle so that the engine speed matches the gearing) to reduce wear on your clutch bands. And if you do throttle-match, then you will certainly use more gas.
I would just forget down shifting coming to a stop altogether. It tends to wear your tranny out quicker ( clutch too if you would happen to have a 5-speed ). I figure its cheaper to replace my brakes than a whole tranny. and yes, I believe most cars kill the injectors under deceleration, so I don't think it would affect gas mileage....even if it did, it would be very, very little.
mack's right, the only time downshifting with a manual is a good idea is around corners, you have more control over the car that way. stopping for lights= all brakes, a normal auto doesn't do anything to slow the car down, now does it?
I don't see why would it wear out the tranny faster than not to downshift with tip. I do it all the time, but not to complete stop, only to the 2nd gear and then let the tranny do the last shift. Just check your multifunction display when you do the "engine braking" and you see that fuel consumption is 0 to the point where the engine again needs fuel to stay running. Someone mentioned it is cheaper to change brake pads than the tranny, true, but the tranny is supposed to last the lifetime of the car, so I believe there is a tip function because it is ment to be used, am I right?
And I consider it to be more safe to keep low gear on when I'm turning from the mainroad, which doesn't have turning lane or something, to the sideroad in case I need fast acceleration to avoid, for example rear ending. I have had couple of incidents where I'm waiting to turn to sideroad and no matter how early I put the turn signal on, there are always people who doens't pay any attention what is going on around them. And instead of turning into oncoming trafic, or just stare your rearview mirror and wait for the other driver smash into you, I prefer to accelerate as much as possible to minimize or completely avoid the damage. May sound a bit stupid but believe me, it has saved me from two accidents. What one of you said, brakes are for braking, that is true also, I do use brakes too, but I want also to be able to take off fast. The car will stop even if you have the low gear on.
But everyone has their own driving habits and I'm not here to tell how everybody is supposed to drive. Just telling mine and I'm noticed it is working for me.
Sorry for going so much off-topic, I got carried away
yes, but downshifting your tiptronic when coming to a stop is somewhat of a shock to the clutch packs and not only that, its harder on the tranny and engine mounts too. I'm not saying you shouldn't do it, for instance, when you wanna accelerate out of a turn, but when coming to a stop in normal driving, I would think its better to use just the brakes than to use the tranny. Automatics by nature don't allow much compression brakeing because of the torque converter ( theres slipage there vs. a solid " connection " like you have with the clutch in a manual tranny).
I tend to use the Tip on my W8 when I'm needing a boost of power for overtaking ...shift in to Tip mode, shift down a few notches to get in the right rev range and then stick your boot down and enjoy the instant acceleration.
As soon as I'm off and running I normally shift the lever back to auto mode and let the box take over the change-ups as it reaches the redline in each gear. Seems smoother somehow...though normally you're up to legal-limit speeds before you've even gone up a gear so can't keep your foot planted for long.
I normally let the gearbox do its own downshifting when slowing down, unless I know I want to accelerate again quickly (like in a corner), when I take over in Tip mode and play with it a little...
It's a completely different driving style from either standard automatic or manual (stick shift), but as you learn your car and how it performs under different situations, you learn how to get the best from it without 'hammering' the engine or gearbox.
Though having said that the W8 does enjoy a burst of speed now and again...it's the crawling through town that kills it I'm sure...