Do today's cars still get their best gas mileage at 50 mph?

Question

Many years ago the federal government said that the best gas mileage was achieved at 50 mph so that is why the speed limit was lowered to 55. Has new engineering changed that?

Answer 1

It all depends on the car and its gears.  If your dashboard has a gauge showing engine rpm, you can use that to determine optimal fuel efficiency speed.

Answer 2

It depends on the car. An LS1(350 HP Chevy V8) Camaro or Trans Am can be at 1900 RPM going 85 on the highway in 6th gear.

Answer 3

No its still the same very mile you go over 55 you loose gas mileage. That why its just best to cruise.

Answer 4

It's all over the map, varying from car to car.  

50 isn't true. It was more like 35-45 back when 55 was made law. (there were no overdrive gears back then). The government might have said 50 because it was more believable.  Today in an efficient modern car it might be 50.  

Aerodynamic drag goes up exponentially - ask any bicycle racer.  That law of physics is hard to beat.  

If a car was meticulously built to have aerodynamics like an airplane - perfectly smooth body and teardrop shape - they might get the sweet spot to 55-60.  Never higher, no way.

But don't trust me, test it yourself with your own car.  Next time you've got a long freeway cruise, drive a few tankfuls at different speeds.  My highest by far was when I kept it around 50. (never tried below 50).