When I first started driving I drove slow bc I thought it would save gas, then I started driving faster when a friend told me you use the same amount of gas whether you drive slow or fast (as long as it’s the same distance), you just would be driving fast for a shorter amt of time and driving slow for a longer amt of time, but at the end you burner thru the same amount of gas. Is this true?
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Specifics will vary by vehicle, but in general, at higher speeds, cars generally start becoming less efficient. This can be especially noticeable at above 70-80mph in my experience.
Depends on the car, but sort of. There’s almost a bell curve. There’s a point where it’s best, and it falls off on either side.
Depends. Pretty much every engine has a peak performance zone – RPMs where fuel efficiency is at its maximum. Lower or higher than that and it will burn more fuel.
Now, the speed that results at that RPM is dependent on what gear you are in. So you might save gas by going faster or slower, depending on RPM, or _both_ assuming you switch gears.
The key to gas mileage is rpms. Doesn’t matter what gear you’re in, your car has a sweet spot for rpms that is the most fuel efficient
In general driving slower reduces the friction due to air resistance which means it requires less energy to maintain the speed and therefore save fuel. The slight issue with this is that engine fuel consumption is not linear. So reducing the speed does not save as much gas as you would expect if you just calculated the air resistance. In fact if you end up in the wrong gear and the engine is running too slow or too fast then it might require more fuel then driving faster. However this is just in certain special cases. So in general you do save gas by driving slower.
It’s not generally true that your fuel consumed just depends on distance. For any particular distance there will be an optimum speed.
Too slow is bad (the engine isn’t getting a chance to be efficient), too fast is bad (air drag is too high). There’s a sweet spot that varies a bit with the vehicle/engine/fuel but it’s typically around 30-50mph.
Each car has its own spot of highest fuel efficiency. If you go just 1mph, it’s almost the same as idling which just is a waste of gas. If you are redlining the engine in the highest gear, you may be going fast, but you are burning way too much fuel due to air resistance among other things.
Many cars are most efficient at around 55-65 miles per hour. This gets them to their highest gear, but with relatively low rpm’s. The air resistance isn’t too bad at this speed either.
Depends on the speed and the car and the tires
The amount of fuel you burn depends on how much power you need, and how much fuel your engine burns just to keep running. All engines consume some fuel just to overcome its own resistances and keep spinning, if you drive too slow then this is the main cause of fuel consumption and you get terrible fuel economy
How much power you need depends on the rolling resistance of the car and the air resistance. Rolling resistance doesn’t change with speed so it takes the same force at all speeds and therefore twice as much power to go twice as fast. Air resistance changes with the square of speed so the power to overcome it goes up by 4x if you double the speed.
If you add the fuel per minute require to keep the engine spinning + fuel to overcome rolling resistance + fuel to overcome air resistance and plot that out across speed, you’ll have a point where you cover the most distance with the least fuel but what speed that is at depends on the car
A car on low rolling resistance tires is going to fare better at middle speeds (20-40mph) than a car with big wide grippy tires that have great traction but high rolling resistance, but that car with the big wide grippy tires might be a lot more aerodynamic have have less wind resistance at highway speeds
It *can* be true, but not always. When it comes to fuel economy, there are a bunch of factors other than just speed. For example, your car will most likely drink less gas with its engine running at 1800 RPM compared to 2300 RPM, and it’s possible to drive at a handful of different road speeds at those RPMs.
Most cars sold in USA, are tuned to give the best gas mileage at about 60 – 65 mph of highway driving. Gear ratios are selected such that motor is in its optimal gas saving range around 2k to 2.5k rpm.
Additionally wind resistance increases non-linearly as higher speeds are attempted.
Net result is that gas consumption increases significantly as one drives at higher speeds.
Another factor which is often overlooked is acceleration. Lead foot driving combined with extended high rpm moves will kill your gas mileage.
Also note that gas mileage in car computers is always measured in mpg not against time. So if your mpg is going up, you are going to take more gas to travel from A to B, no matter how much time you take.
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