Is fuel consumption dependent on engine RPM or vehicle speed?

Question

In other words, do you burn more gas if you're:

1) Travelling at 50mph @ 3000rpm vs 50mph @ 5000rpm?
2) Travelling at 80mph @ 4000 rpm vs 30mph @ 7000 rpm?

Because I've always wondered how is it possible that city mileage is lower than highway mileage. I've always thought that travelling at higher speeds would burn more gas (ex. highway driving), but I was surprised to find out that city mileage actually gets worse mileage despite lower average speed. Can someone please explain why?

Answer 1

Both those are hand in hand - consumptinos is ment with demand - the more you request the more it waists hence gas milage being lower at higher RPM even thou you are going 30 miles an hour.

Answer 2

Both are a factor, but the main one is RPM. If the engine is running twice as fast, then it will need more fuel. If a car is going faster it will need more fuel to keepp it up. In the city you keep accelerating and raising the RPM, you also sit at stoplights taking fuel and not moving. On the highway once you get to speed all you have to do is keep it there

Answer 3

City milage is generally lower because you are starting and stopping more. According to Newton's first law of motion it takes more energy to start a body moving than it does to keep a body moving because of momentum. Think about it. When you step on the gas to go you push it quite a ways down, once you reach your cruising speed, you ease off on the gas. So fuel consumption is not dependent on RPM or speed. It is dependent on how far the accelerator is depressed. Optimum fuel milage will be attained at different speeds for different cars depending on aerodynamics, gearing, and engine efficiency.

Answer 4

City is worse because it's stop and go. Every car has a certain speed for optimum mileage. Some are 60, some are 70, etc

Answer 5

when city driving, the car is revving up and down more often, when shifting gears. so the average rpm while in the city may be 3200 rpm or so, when on the highway you are at a constant speed and somewhat constant rpm of around 2900 rpm or so. so less rpm is less fuel used

Answer 6

Depends on how much WORK, the engine has to do at any speed. City driving is full of work where hiway driving is at a constant speed requiring less work

Answer 7

The optimum speed for an average saloon engine is 56mph / 30000 rpm

Answer 8

that would be of the stopping and starting #1I say 50 at 3000 would use less gas #2 ? there are other factors like weight