tdrive2 wrote:
Time to change them back, oil is around 40 $ a barrel. Cars are more efficient at higher speeds now. They are also safer.
I disagree with the efficiency part here. The formula for the required power to overcome the air drag is:
Where p-creature is Greek "Ro" (density of fluid/air), A is the area of the front of the object (against which the fluid is pushing), and Cd is the drag coefficient, around 0.25-0.45 for cars, and v is velocity in m/s (that is relative to wind - wind blowing against you increases air drag and vice versa). The engineers have reduced the Cd to 0.25, but there is nothing that can be done otherwise unless the car is really low, with a very little front area. And the drag is a function of a square of the speed, and the power output required to susteain the speed is a function of a cube of speed, so it will take 8 times as much energy (read: fuel) to sustain double the speed. If you have read about the Bugatti Veyron, at top speed of 375 km/hr it uses up 78L of fuel for 100 km (3 MPG), while highway rating is 20 L/100 km.
Of course there are many factor that affect this fuel efficiency, like the efficiency of transmission, engine power output at certain RPMs, the torque developed, so most cars have "best mpg" speed of in-between 90 (older squarish Volvos and Olds, etc) to 130 (higher-end cars) km/hr. Going faster than that simply uses up more fuel.
_________________
"The more laws, the less justice" - Marcus Tullius Cicero
"The hardest thing to explain is the obvious"
www.OHTA.ca &
www.OntarioHighwayTrafficAct.com