Why is it better for you car to be in a lower gear to go downhill but also uphill?
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For a steep hill, a lower gear will allow for engine braking. If you are using your brakes continuously they will heat up and possibly become less effective or fail as they get hotter. Being in a low gear will help counter that because the engine will help with braking.
Internal combustion engines provide the most power/torque within a specific RPM range, which means you need a transmission to match the engine’s speed to the desired speed of the wheels.
Lower gears require more revolutions of the motor to get one revolution of the wheels, but the lower speed comes with increased power. Higher gears use fewer revolutions of the engine for a single revolution of the wheels, which allows much faster speeds, but lower power- you can’t start in high gear, for example.
So, going up a hill, the vehicle will slow down and require additional power to overcome the gradient- it’s harder to go up a hill, so downshifting allows you to get more power to go up the hill.
Going downhill, you may want to slow your vehicle, so putting it in a lower gear and allowing the engine to act as a drag on the vehicle’s forward motion allows you to rely on the brakes less. This is not typically something you should rely on heavily with most passenger vehicles, but can help keep you from accelerating too quickly when going downhill without having to ride the brakes and heat them up.
Depends on your speed and your goals and the traction and weather and how much room you have in front of you and the engine characteristics and all sorts of shit, I think this question is not very answerable unless it’s more specific
Usually to maintain a reasonable RPM, you enter lower gears going uphill
And when going downhill, you may be in a high gear if you wish to go fast or coast and use less fuel, but if you’re trying to go slowly and be more defensive you can enter a lower gear while going downhill to maintain more control and use engine friction as a means of engine braking to reduce speed and reduce strain on your brakes.
High gear going downhill is more fuel efficient but usually less control because the increased friction of the engine (higher rpm) in a low gear increases the drag of the drivetrain and slows you down, if you wish to brake or be in a more defensive posture.
Super steep downhill in a city and it’s busy and you have a heavy load and might need to stop quickly? Low or medium gear.
Gentle sloping massive downhill in the middle of the country with nobody around and lots of room? High gear, more fuel efficient, faster.
Low gear = wheel spin slow, but with more power
High gear = wheel spin fast, but with less power
When you’re going uphill, you need more power, and speed is not as important, and when you’re going downhill, the power doesn’t really matter, but keeping your speed low is helpful. Both are situations which prefer a low gear.
When you’re on a flat, power isn’t important, but you do need speed. So a higher gear is ideal on a flat, such as a highway. Additionally, your car gets better fuel efficiency on a high gear, because a high gear limits the power, and therefore limits the energy it can use. Fuel is the source of energy in a car, so limiting energy use, means saving fuel.
Of course this is for driving on the road, and not for racing. When you’re racing the goal is to keep your car in the gear that give you the most power at any given moment, but not so you can climb better, rather so you can accelerate faster.
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