Driving at 75 mph burns 27% more fuel and most drivers have no idea

Let's be honest. No one likes to stand at the gas pump and watch the dollars spin like a slot machine. With fuel prices taking a serious bite out of your paycheck, second only to your car payment or lease, wringing every mile out of every gallon isn't just smart, it's a necessity.

Here’s something most drivers don’t know. The speed you drive has a dramatic effect on the amount of fuel you burn, and if you’re regularly cruising at 75 mph on the highway, which is pretty standard on an American interstate, you’re silently torching your gas money without even knowing it.

The sweet spot most of us blow by
There's an optimum speed range for efficiency in your car. A study of 74 different vehicles by the Oak Ridge National Laboratory found the sweet spot to be between 40 and 50 mph. Once you get above 50 mph, your fuel economy starts to fall, and fall fast. At 80 mph, you are consuming approximately 27% more fuel than you would at 60 mph.


Think about that in dollars. If your car gets 32 mpg at highway speeds and you fill up every week, that inefficiency adds up to hundreds of dollars a year, money that could go towards a car insurance payment, a weekend trip, or just some breathing room in a tight month.

Here's how the Department of Energy puts it: for every 5 mph you drive over 50 mph, it's like paying an extra $.28 per gallon for gas. You wouldn't ignore a 28-cent increase at the pump. So why do we ignore the speed that does it?

So why does speed hurt fuel economy so badly?
The short answer: air hates you if you go fast.

The longer answer is that there is something called aerodynamic drag. This is the resistance your car experiences as it pushes through the air. At low speed, the resistance is okay, but as you accelerate, physics changes dramatically. Drag is not linear with speed. It rises with the square of your speed. So when you go from 45mph to 75mph, you are not just going 1.7 times faster, you are fighting roughly 2.8 times as much air resistance.

A review of research published through the USC Viterbi School of Engineering reveals that aerodynamic forces affect fuel consumption more at highway speeds than at lower speeds, and the faster you go, the more pronounced the effects. At high speeds, aerodynamic drag can account for nearly half of your car’s overall fuel consumption.

Your engine, then, works overtime. This takes more gas to maintain that speed against the increasing wall of air resistance. The faster you go, the more this happens, exponentially.

What this means for your wallet right now
You don't have to drive like it's a Sunday country cruise to make a difference. Small things matter.

Slowing down from 75 mph to 65 mph on your everyday commute or road trip can greatly affect your fuel economy. On flat highways, keep a steady speed with cruise control; erratic acceleration is another silent gas waster. If you’re piling a rooftop cargo box on your car, know that it can cut your highway fuel economy by as much as 25%.

None of this requires a new car, a hybrid, or a lifestyle overhaul. It just requires understanding what's happening under the hood and under the laws of physics, every time you put that accelerator towards 80.

Gas prices may be out of your control. Your right foot isn't.