Fuel consumption & Speed?

Question

Its my 2nd post here. (Against my first question, I got v. good response and hope to receive the same this time too).

My question is as below.

I have a petrol Car and its average is 14 Km per Liter.
Is it true that if I drive a car at high speed then petrol consumption will be less ? Or vise versa ?

For example, I drive it at 60 Km/hour speed and note down its fuel average as 14 Km/Liter. Now if I will drive it with speed of 80 Km/Hour or say 100 Km/Hour, then petrol consumption will be 15 Km/Liter or 16 Km/Liter ?

Conversely, if I drive it at 30 or 40 Km/Hour speed, then will its average will remain same (14 KM/Liter) or will come down little bit like 10~12 Km/liter ? As I understand that at small gear, fuel consumption is more as engine is working with more power.

Anyhow, just wanted to know is it true or not ? Plz comment !!!

xxx

Answer 1

Yes, the higher your R.P.M.s the more fuel you use at any speed. I.E. my rover gets better milage on long country roads then the Highway beacause of the gearing in the tranny...:-)

Answer 2

Gas mileage, as it is refered to here in the U.S., is at it's optimal at different speeds for different cars. Most cars are designed to attain optimal mileage at around, or just under 55 miles per hour, or 95 kilometers per hour. Engine efficiency is achieved at a specific RPM, maybe 1750 or so, and the highest gear at the optimal RPM achieves the best mileage.
Mileage is a measurement of fuel usage per mile, not fuel usage over time, therefore low RPMs mean nothing, as you get nowhere. Anyone with a mileage meter on their vehicle will be able to tell you that travelling at the lowest rate of speed without bogging down will provide you with the worst possible MILEAGE, as your engine is fighting it's own desire to stall, as well as the resistance of pushing the vehicle forward. Also, engine oil suspends parts better the faster the engine is turning, providing for less, not more, friction. Again, higher efficiency.

Answer 3

Indicated Airspeed decreases because it is measured by ratio of ram air pressure and static air pressure. Because the air is thinner/ less dense, the ram air pressure decreases more than the static pressue, thus showing an lower indicated airspeed. Because the air is less dense, compression in the engine cylinders is reduced, thus the engine creates less power. Engine combustion is a very fine fuel to air ratio, and with less air, fuel consumption is lower. However, as an propeller aircraft ascends, temperture decreases thus True Airspeed is higher. (True Airspeed is Calabratied Airspeed corrected for non standard temperture). So, although the airspeed indicator is showinig a decrease in airspeed, in real life, the aircraft is moving through the air faster than indicated. Ground speed is dependant on the wind speed and direction.

Answer 4

If you drive faster, your fuel consumption will be HIGHER. If you drive slower, your fuel consumption will be lower -- down to a point. And that is not counting stop and go driving.

The drivetrain has friction. The faster the car goes, the faster the bearings and other parts have to turn -- and the more friction. More friction= more waste = worse fuel mileage.

If you drive in a lower gear with high engine rpm's, yes, your fuel consumption will be higher.

Answer 5

The most fuel that you will burn is getting the automobile moving. Once the auto is in motion then fuel consumption is stabilized until you have to slow down or stop then move again. This is why highway mileage is better than city mileage. I have a car that tracks instant mpg and I get the best mpg at about 60 mph.

Answer 6

You need to look at the transmission of the vehicle the axle ratios, not just the engine and fuel. The axle at 3000 engine rpm at 4th gear is the same at 3000 rpm and 1st gear. Manual transmissions drivers can adjust this as they drive with more attention, automatic shifting might have a switch in the vehicle and are safer.

Some are for off road, towing, construction, street, highway or other. If you have the sales documentation of the vehicle it might say: highway, city, off-road, trucking, mass transit.
Vehicles, passenger weight (300lbs +), cargo are problems also.

Answer 7

the best mileage is about the slowest speed in fourth or fifth, without lugging the engine. High gear, low speed, but not too low for the engine, coast downhill in neutral.

Answer 8

Simple answer;

The faster you drive the more energy is required to overcome wind resistance and rolling resistance of the tires. And it takes more energy to move the weight of the car at a faster speed.
So you burn more fuel going faster.

Answer 9

The short answer is you will use more gas at faster speeds. Your observations are flawed.