You've probably heard that speeding hurts your gas mileage, but here's what it actually costs: each 5 mph you drive over 50 mph is like paying an additional $0.21 to $0.27 per gallon for gas, according to the U.S. Department of Energy. That's not a typo—your speedometer and your wallet are more connected than you think.

The original fact floating around the internet claims this penalty kicks in at 60 mph and costs only $0.10 per gallon. That's outdated information. The EPA's current data shows the efficiency drop starts at 50 mph, and with modern gas prices, the cost is more than double the old estimate.

Why Does Speed Kill Your MPG?

The culprit is aerodynamic drag, and it doesn't play fair. While drag is responsible for only 20% of fuel consumption in city driving, it accounts for 50% of fuel used during highway driving. The faster you go, the exponentially harder your engine works to push through the air.

Here's where the math gets painful: at 70 mph, your car fights against four times the aerodynamic force it faces at 35 mph. It's like the difference between walking through your living room and walking through shoulder-deep water.

The Percentage Drop Is Worse Than You Think

Let's talk numbers. Compared to the optimal speed range of 40-50 mph, here's what you lose:

60 mph: 3% less efficient
65 mph: 8% less efficient
70 mph: 17% less efficient
75 mph: 23% less efficient
80 mph: 28% less efficient

One particularly striking study found that a light-duty vehicle traveling at 80 mph used 27% more fuel than the same vehicle at 60 mph. That's more than a quarter of your gas evaporating into thin air—literally.

Your Engine Wasn't Built for the Autobahn

Most passenger vehicles hit their sweet spot between 40 and 60 mph. Push beyond that, and you're forcing your engine to operate outside its optimal design range. It's working harder, burning more fuel, and delivering worse results.

Each 5 mph over the 50 mph threshold reduces fuel economy by about 7%. Do that math over a tank of gas, then over a year of commuting, and you're looking at hundreds of dollars literally flying out your tailpipe.

The Real-World Impact

Think about your daily highway commute. If you're cruising at 75 mph instead of 60 mph, you're burning through roughly an extra gallon of gas for every 50 miles driven (depending on your vehicle). Over a year, that adds up to genuine money—enough for several nice dinners or a weekend getaway.

The irony? You're spending more to save maybe 10 minutes. The physics don't care about your schedule. Air resistance increases with the square of velocity, which is a fancy way of saying that small speed increases create disproportionately large efficiency losses.

So next time you're tempted to push 80 on the highway, remember: you're essentially volunteering to pay a 28% surcharge on every gallon in your tank. Your car will get there just fine at 65. Your wallet will thank you.

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