Is it true if you drive slower you save gas??

Question

I heard something along the lines that if you drive slower, you don't use as much gas. But wouldn't it use more gas since it takes you longer to get to your destination?

Answer 1

Stop speeding. The faster you drive, the more gas you use, the more money you spend. Each 5 mph over 60 is equivalent to paying an extra 10 cents per gallon for gas....

    Avoid aggressive driving and quick starts and stops. At highway speeds, you'll lower your gas mileage by about 33 percent. By maintaining a constant speed and driving sensibly, you could save as much as 50 cents a gallon.

I'm not going to discuss the time cost of slowing down. For arguments sake, assume that you're indifferent between sitting at home or sitting in your car. Is it true, regardless of your car make, model, and condition, that driving 65 instead of 60 increases average fuel cost by about 10 cents per gallon? I'd say yes, with anecdotal caution.

It seems about right, but only if gas prices are about $2.50 per gallon. This is confirmed by a casual analysis of the graphics provided by the government.

Answer 2

IT DOCENT MATTER WHAT YOU DO YOU STILL GONNA USE GAS NO MATTER WHAT & YOU CANT DRIVE SLOW ON SOME STREET'S

Answer 3

it uses more gas if you accelerate really fast and make short stops a lot. But driving at a constant rate of 55 mph is the best for not using up gas

Answer 4

I measure my fuel economy all the time, my truck, a 1996 Ford F-250 diesel will get 16.68 mpg running at 2700rpms and 75 mph, I slowed down to 70 and got @ 17.88 mpg. I slowed down to 65, it ran 18.5 mpg, I slowed to 60 and got 21.44 , now I am running at 50 mph, trying to keep my rpms under 1500 at all times, I have driven 104 miles so far and so far the needle has barely moved. Not bad for a 9500 pound truck. It may take a little longer, I drive 24 miles and it does take 15 more minutes, thru town, but your engine runs slower, so it is not using as much energy, my truck is doing a little more than idling, I will once a month or so, run fast to make sure there is no buildup in the exhaust system, not sure if there is a truth to that, or myth.

Answer 5

I'm sure you could find solid numbers but there is a huge change in gas mileage between 55mph and 70mph.

You know that "the gubment' is talking about bringing back the  national 55 mph speed limit, don't you?

Answer 6

You're very perceptive -- driving slower also takes longer to get there.  And it works like you think up to about 40 mph.

But one of the factors of fuel economy is called aerodynamic drag, and that factor goes up exponentially.  That's a mathematical term meaning it increases much faster than 1:1.  Aerodynamic drag goes up as a second order, also called "it squares".  If you double your speed (times 2), your aerodynamic drag goes up 2x2=4.  If you triple your speed (times 3), aero drag goes 3x3=9.  Quadruple, 4x4=16.  That doesn't sound like much yet, but you can see where this gets steep eventually.

So below about 40 mph, aerodynamic drag is pretty minor to a car. By 80 mph, almost all the car's energy is going into pushing the wind!   Sure you've cut your travel time in half, but you've increased your aero drag x 4, so it's actually twice as bad as before.

Where is the sweet spot on a car?   A lot of people would like to believe it's 55 mph, but that's wishful thinking. I think it's more like 40-45, but it varies somewhat from car to car.  One guy insisted his motorcycle's sweet spot is at 90 mph, because he tested it on a dynamometer.  Very scientific of him but he forgot - a dynamometer is a set of rollers in a room.  There's no aerodynamic drag on a dynamometer!  He totally forgot to factor that in!  By excluding aero drag, indeed, things work just as you thought they would.  If only we could for real.

Answer 7

too slow is bad too, 55 mph is better

Answer 8

yes you will get better gas mileage.

Answer 9

There are just a few factors that determine how much fuel you use, and without switching cars there are only a couple that you can affect in any way.

The fuel you use is used for only four things -- overcoming inertia, gravity, drag and friction.

Accelerating to a higher speed means that your foot is asking for the extra power to overcome inertia longer.  Using the physics term, you are doing more work, so it takes more energy.

Accelerating harder is more work, so putting the pedal to the metal uses more gas.

Cruising at a higher speed is more work because wind, rolling, and internal resistance (friction) are all higher at higher speed.  Add a hill, and you increase the amount of work being performed again (overcoming gravity), so you just compounded the energy cost of the higher speed.

In an ideal world, every erg of energy you used to accelerate or climb a hill would be returned to you when you slow down or go back down the other side of the hill, but factors like friction, tire heating, gear ratios, torque converter slippage and unlocking, etc., etc., make it far from ideal.

I hope this helps.

Answer 10

there is an ideal speed i think it is 40 ish, faster or slower uses more gas