I drive a small automatic car. For the most part, it struggles a bit with steep uphills, and picks up speed when going downhill. That’s to be expected.
But then I noticed some downhills actually slow it down. I’ve noticed during a two-hour motorway trip I often do to visit family, there are some specific downhills, not all, just some, where my car always slows down and I have no idea why.
Ideas?
This is very likely the reason. Not all downhills will induce it, but the automatic is down-shifting to slow your acceleration. There are various ways for your car to know but manufacturers want the driver in control, not the environment. Depending on the car and speed you may not hear it, but when it slows down does it sound like the engine is revving higher?
It also helps keep brakes cool, important for mountain driving.
One of my cars hardly does any automatic engine braking. My other vehicle will keep or decrease speed down long hills/mountains. No noticeable change in engine noise at all. Makes long trips through the mountains much easier, especially because it’s a heavy vehicle and overheated brakes is a very real concern.
What happens when the brakes get too hot? Do they gently stop working or can they just explode or something?
Optical illusion is most likely the reason instead of engine brake if your vehicle slows down significantly in certain areas and doesn’t on other downhills with “similar” angle.
There is this slope near a waterfall around where I live. If you put your car in neutral gear at the bottom of the slope, it rolls “up” the hill. We named it magnetic hill back in high school, but I later found out that it is just an optical illusion that happens everywhere around the world. Basically some uphills look like downhills and vice versa. Google “gravity hill”.
Okay. I’ll fix a marked water bottle to the dashboard for the next trip, and see how the level stacks against the mark.
The water level will be affected by the car’s acceleration, which is likely also affecting your inner ear and causing the illusion in the first place.
Sounds like engine braking
Is it a hybrid?
How steep of a downhill and how fast are you going? Gravity will pull depending on the angle of the hill, wind resistance increases with the square of your speed. There will always be a speed where the force pulling you down/forwards will be the same as the force slowing you down due to wind resistance. If you go slower, your car will speed up towards that speed, if you are already faster, it will naturally slow down with no input from the engine or your brakes.
Well, it’s a 110km limit zone for the most part, I’m usually sitting somewhat under the limit but typically above 100. I don’t know how steep these slopes are. Maybe I’m under/overestimating them as a consequence of driving, slopes become obvious on foot. They don’t appear to be particularly steeper that others where my car doesn’t do this. They are certainly not very steep though, because there are a few of those and I gain and lose a lot of momentum on them.
