f you drive a standard, you downshift for hills. Why don't people also downshift auto transmissions? Almost everyone I know just leaves it in "D" and rides the brakes down. Is there some harm to an auto going downhill at a higher RPM but a slower speed?
I M RIGHT
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WHen you use your brakes going down a hill, you wear the linings/pads a little bit. When you use a manual transmission, you wear the clutch, throwout bearing, transmission bearings, engine bearings, piston rings, valve guide seals etc. a little bit. When you downshift an automatic, you wear all that, plus the transmission bands/clutches and you heat the transmission up. Occasional downshifting for a steep hill is negligible.......doing it frequently, brake pads are a lot cheaper to replace than engines and transmissions.
AlCapone
When your transmission is in the "D" position, that's not simply one gear -- it's every gear and because it's an "automatic" transmission, the proper gear is always selected for the situation, such as going up a hill. Many automatics will also shift into a lower gear when going down a hill if you use the brakes initially to slow the speed -- which avoids having to "ride" the brakes. There is no harm in allowing the engine to slow a car going downhill.
Anonymous
I drive an automatic transmission vehicle and I downshift when going down hill. It saves wear and tear on the brakes and I am going slow enough to downshift to a lower gear to help slow the vehicle down.
The Devil
Riding the brakes down a long hill can overheat them, causing brake failure when brake fluid starts to boil. It can also warp disc brakes which will cause the steering to shimmy when brakes are applied from then on. You can avoid expense by being smart. Modern cars use no more gas from downshifting because the computer sets the fuel injectors at idle regardless of the engine braking increasing rpm.
Andy
Most newer cars will downshift themselves if you have the cruise control set while going downhill. It does not harm them to downshift them if done properly. My Ford F150 has a manual option for shifting. I use it quite a bit going down hills if I need to control the speed (such as a school zone).