Why does driving slower save fuel or is more fuel efficient, compared to driving faster to the same distance?
I’ve heard in the news that some airline operators have instructed their pilots to fly their planes slower to conserve fuel, so I wonder what has speed got to do with fuel usage.
I’ve heard in the news that some airline operators have instructed their pilots to fly their planes slower to conserve fuel, so I wonder what has speed got to do with fuel usage.
Because for example, if a driver reaches a place 10kms away from start in 15mins on fast speed and if another reaches the same distance in 30mins on slow speed, then won’t the slow driver spend as much fuel as the faster driver as he drove for a longer period of time to the same distance as him?
Isn’t FAST SPEED & LESS TIME equal the same amount of fuel usage compared to SLOW SPEED & MORE TIME?
Please explain in detail as I’m confused.
Thanks.
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Filed under Gas Conservation FAQ by on Feb 21st, 2011. Comment. 
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Comments on Why does driving slower save fuel or is more fuel efficient, compared to driving faster to the same distance?
works the same with any motor faster you go the more fuel you use
Driving faster makes the engine have to work harder, faster and as a result you burn more fuel. Take yourself for example running 1 mile fast, you would burn less energy walking than running.
What do you do when you want to go faster in your car? You push down the gas pedal so that more gas is used to make the car go faster. Same in a plane.
More fuel is needed for the acceleration to get to the higher speed. It doesn’t take as much fuel to maintain a slower speed.
figure it out. the faster you go, the more gas your giving it and the slower you go, the less gas your giving it.
Our local radio show did a test. Two identical cars drove 400 miles. One at 65 and the other at 75. Yes the 75mph car got there first but the slower car save a lot of fuel. about 5 mpg
U can answer that question by ur self by looking at the formula of kinetic energy, KE=(1/2)mv^2
m=mass, in this case of your car
v= (d/t) =the speed of your car
Let’s say u r driving from home to work(without braking), from the equation, u know the mass of ur car(m) and the distance u want to travel(d) don’t change. So time (t) is the only thing you change here. Since speed is distance (d) divided by time(t), u can see that when time is reduced(get to work sooner) the energy(KE) is increased. So more energy=more fuel needed.
Another (more important) reason u’ll burn more fuel driving fast is whenever u apply brake, this kinetic energy is converted to heat(u’ll notice that ur brake pad n rotor get hot). Ur hwy driving gets better fuel efficiency than ur city driving because ur car doesn’t lose as much kinetic energy, through braking, when u drive on hwy….unless it’s a rush hour hwy in a big city.
In addition to Musikpal comments:
Musikpal analysis of start and stop are correct, however are missing one more term for air resistance.
When you stick your hand out the window you can feel the “wind” pushing it back. While vehicles are designed to be as aerodynamic as possible, they still have that wind force (aerodynamic drag) pushing them back.
The problem with drag is that it is related to the square of your speed. Meaning that when you drive two times faster than normal, the drag isnt two times stronger, it is actually four, similarly driving 3 times faster the drag is 9 times (ignoring air seperation effects).
This means your engine has to more energy to maintain your speed at higher rates of speed, than at lower.