why do all cars slightly move forward when your foot is on neither the gas nor the break?

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why do all cars slightly move forward when your foot is on neither the gas nor the break?

In: Engineering

6 Answers

Anonymous 0 Comments

In true ELI5 fashion:

Even when no pressure is put on the gas peddle, a small amount of power is still being produced by the engine and this power is attempting to move the car forward. When the brake is pressed it is able to overcome the power of the engine and keep the car stationary. When both peddles are not pressed, the small amount of power coming from the engine makes the car crawl forward.

This explanation doesn’t use any words a 5 year old wouldn’t understand such as automatic, manual, transmission, torque converter, clutch, ect.

Anonymous 0 Comments

>break

**B** **R** **A** **K** **E**

“break” is smashing something into tiny pieces.

This doesn’t happen with “all cars”. This only happens “naturally” with automatic transmission vehicles that use a torque converter… I guess the ELI5 explanation is that it “leaks” a little bit of power from the idling motor to the wheels, so the car will be pushed forward slightly when set to “Drive” as long as the engine is running.

Manual transmission vehicles don’t do this. The engine will stall if you try to come to a complete stop with the clutch engaged (or you’ll damage the clutch). If you disengage the clutch it’s like being in neutral in an AT vehicle, and it won’t creep forwards.

Electric cars and vehicles with fancy things like a CVT (continuously-variable transmission) normally wouldn’t do this… but because people are used to it with regular automatic transmissions (and it can be helpful for parking) they actually fake this behavior and deliberately transmit a small amount of power to the wheels when you take your foot off the brake. IIRC in some electric cars you can toggle this behavior on and off.

Anonymous 0 Comments

Are you talking about the idle speed or when you park?

Anonymous 0 Comments

This would only happen on a car with an automatic transmission/torque converter because once you put the car in drive the spinning of the engine even at idle is transferred to the wheels through the TC ever so slightly. If the car is an automatic with a cvt they’re electronically controlled and won’t engage until the gas is pressed.

A manual transmission car will just stall because the connection between the engine and wheels is more direct and the idle rpm would not be enough to move it.

Anonymous 0 Comments

In simple terms if you’re driving an automatic and the car is in gear the engine never really stops running and generates enough force to move the car forward

Anonymous 0 Comments

Not all of them.

Might be that you’re on a slight incline forward.

But your formulation makes me guess you only refers to automatic cars. If you’re in D(rive) then the car clutch will stay engaged to be ready giving you that slight move.

If you change to neutral, then there will be no drive.

Edit, damn bilingual autocorrect