Downhill Downshifting

[supmet]

Originally Posted by reesesyum

This doesn't help the engine brake. As another poster pointed out - the downshift does not significantly slow the car down. It continues at the same speed, just with higher RPMs.

It may not seem significant on steep hills, but it is definitely helping you.

Originally Posted by reesesyum

I also disagree that this isn't bad for the transmission. As other posts state, this is putting additional, unnecessary stress on the transmission.

As others have pointed out, they have been downshifting on hills for 10s of thousands of miles. It does stress the engine and transmission some, but by the time you notice any wear, you will have saved 10 or so brake changes.

Originally Posted by reesesyum

There is also the problem of performance if you want to then pick up speed after the downshift. This is like trying to pedal faster going downhill when you're in the lowest gear on your bike - nothing happens.

If you're trying to pick up speed why are you braking? With the auto I can downshift into 3 going down a hill to maintain speed, and still have plenty of power to motor around people.. I'm not sure I get what you're worried about here

Originally Posted by reesesyum

What I find curious about this is that if you depress the brakes more fully, but still short of a full stop - due to an unexpected slowing in front of you for example- the trans does not downshift. The downshifting only occurs on relatively light application of the brakes - which in my previous driving has been a fairly common occurrence. I just find the whole thing curious.

I'm guessing on emergency braking you are slowing too fast for the synchros to catch

[reesesyum]

Originally Posted by supmet

If you're trying to pick up speed why are you braking? With the auto I can downshift into 3 going down a hill to maintain speed, and still have plenty of power to motor around people.. I'm not sure I get what you're worried about here

Not worried, but it definitely zaps power. I think my bike analogy holds. Occasionally you'll want to pick up speed after braking going downhill. I live in Los Angeles, and there's traffic. Going downhill, some unnecessarily brake, causing you to (lightly) brake to slow down. The engine then rears when the auto downshifts. Then you maneuver around them and want to pick up speed - but there's less power because you're in a lower gear.

Originally Posted by supmet

I'm guessing on emergency braking you are slowing too fast for the synchros to catch

When I emergency brake - I certainly don't brake slowly. The slow braking comes from non-emergency braking. Lightly applying the brakes to slow down a little causes the downshift. Emergency braking when fully applying the brakes does not cause the trans to downshift, though in that case you're coming close to a full stop, so that would be expected/unnoticed/irrelevant.